Multivariate normative comparison, a novel method for more reliably detecting cognitive impairment in HIV infection

A longitudinal evaluation of personalized intrinsic network topography and cognitive decline in Parkinson's disease

Resting state functional magnetic resonance imaging (R-fMRI) offers insight into how synchrony within and between brain networks is altered in disease states. Individual and disease-related variability in intrinsic connectivity networks may influence our interpretation of R-fMRI data. We used a personalized approach designed to account for individual variation in the spatial location of correlation maxima to evaluate R-fMRI differences between Parkinson's disease (PD) patients who showed cognitive decline, those who remained cognitively stable and cognitively stable controls. We compared fMRI data from these participant groups, studied at baseline and 18 months later, using both network-based statistics (NBS) and calculations of mean inter- and intra-network connectivity within pre-defined functional networks. The NBS analysis showed that PD participants who remained cognitively stable showed exclusively (at baseline) or predominantly (at follow-up) increased intra-network connectivity, whereas decliners showed exclusively reduced intra-network and inter- (ventral attention and default mode) connectivity, in comparison with the control group. Evaluation of mean connectivity between all regions of interest (ROIs) within a priori networks showed that decliners had consistently reduced inter-network connectivity for ventral attention, somatomotor, visual and striatal networks and reduced intra-network connectivity for ventral attention network to striatum and cerebellum. These findings suggest that specific functional connectivity covariance patterns differentiate PD cognitive subtypes and may predict cognitive decline. Further, increased intra and inter-network synchrony may support cognitive function in the face of PD-related network disruptions.

Brain N -acetyl-aspartyl-glutamate is associated with cognitive function in older virally suppressed people with HIV

OBJECTIVES

Cognitive impairment persists in virally suppressed people with HIV (VS-PWH) especially in higher order domains. One cortical circuit, linked to these domains, is regulated by N -acetyl-aspartyl glutamate (NAAG), the endogenous agonist of the metabotropic glutamate receptor 3. The enzyme glutamate carboxypeptidase II (GCPII) catabolizes NAAG and is upregulated in aging and disease. Inhibition of GCPII increases brain NAAG and improves learning and memory in rodent and primate models.

DESIGN

As higher order cognitive impairment is present in VS-PWH, and NAAG has not been investigated in earlier magnetic resonance spectroscopy studies (MRS), we investigated if brain NAAG levels measured by MRS were associated with cognitive function.

METHODS

We conducted a retrospective analysis of 7-Tesla MRS data from a previously published study on cognition in older VS-PWH. The original study did not separately quantify NAAG, therefore, work for this report focused on relationships between regional NAAG levels in frontal white matter (FWM), left hippocampus, left basal ganglia and domain-specific cognitive performance in 40 VS-PWH after adjusting for confounds. Participants were older than 50 years, negative for affective and neurologic disorders, and had no prior 3-month psychoactive-substance use.

RESULTS

Higher NAAG levels in FWM were associated with better attention/working memory. Higher left basal ganglia NAAG related to better verbal fluency. There was a positive relationship between hippocampal NAAG and executive function which lost significance after correction for confounds.

CONCLUSION

These data suggest brain NAAG serves as a biomarker of cognition in VS-PWH. Pharmacological modulation of brain NAAG warrants investigation as a therapeutic approach for cognitive deficits in VS-PWH.

Mode of HIV exposure and excess burden of neurocognitive impairment in people living with HIV: a protocol for systematic review and meta-analysis of controlled studies

BACKGROUND

Chronic HIV infection significantly elevates the risk of brain pathology, precipitating neurocognitive impairment (NCI) among people living with HIV (PLWH). The diagnosis of NCI in PLWH hinges on evaluating deviations in neuropsychological test performance in comparison to HIV-seronegative normative controls. However, the adverse psychosocial conditions experienced by PLWH can also result in reduced test performance, potentially confounding the accurate NCI attribution to HIV infection. This planned systematic review aims to investigate potential disparities in the excess burden of NCI among PLWH in two groups of studies: (a) studies enrolling controls who shared a similar mode of HIV exposure (MoHE) with the PLWH participants (MoHE-adjusted) and (b) studies enrolling normative controls or controls without undefined MoHE (MoHE-naive).

METHODS

We will systematically search five electronic databases (MEDLINE, Embase, PsycINFO, Web of Science, ProQuest) and registries (OpenGrey, ClinicalTrials.gov, ISRCTN registry). Studies reporting NCI in PLWH and HIV-seronegative controls with cross-sectional or baseline measurements, published from January 2007 to September 2023, will be included. To be classified as MoHE adjusted, a study must evidence ≥ 90% enrolment of both PLWH and their seronegative controls from the same MoHE group (e.g. men who have sex with men, people who use drugs or alcohol). Reports of test performance scores will be transformed into NCI proportions using simulated score distributions, applying a global deficit score cut-off ≥ 0.5 to estimate NCI cases. The Newcastle-Ottawa scale adapted to the purpose of the review will be used to appraise study quality. Random-effects meta-analysis will be used to pool the excess burden of NCI in prevalence ratios and test the difference between MoHE-adjusted and MoHE-naive studies. Furthermore, subgroup analyses and meta-regression will be undertaken across categorical study-level covariates (e.g. study locations, NCI diagnostic criteria) and continuous/ordinal covariates (nadir CD4, number of neurocognitive domains assessed), respectively.

DISCUSSION

This systematic review will contribute towards a greater appreciation of the unique psychosocial conditions of PLWH that are missing from the current case definition of HIV-associated neurocognitive disorder. The findings will additionally highlight possible disparities in the distribution of the excess burden of NCI by MoHE groups, thereby guiding the prioritization of mitigation efforts.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021271358.

Neurocognitive Dysfunction With Neuronal Injury in People With HIV on Long-Duration Antiretroviral Therapy

BACKGROUND AND OBJECTIVES

Neurologic outcomes in people with HIV (PWH) on long-duration antiretroviral therapy (ART) are not fully understood, and the underlying pathophysiology is unclear. To address this, we established a cohort of such individuals and compared them with HIV-negative controls using a novel matching technique. Both groups underwent extensive cognitive testing, evaluation for psychiatric measures, and MRI and CSF analyses.

METHODS

Participants underwent comprehensive neuropsychological testing and completed standardized questionnaires measuring depressive symptoms, perceptions of own functioning, and activities of daily living as part of an observational study. Brain MRI and lumbar puncture were optional. Coarsened Exact Matching was used to reduce between-group differences in age and sex, and weighted linear/logistic regression models were used to assess the effect of HIV on outcomes.

RESULTS

Data were analyzed from 155 PWH on ART for at least 15 years and 100 HIV-negative controls. Compared with controls, PWH scored lower in the domains of attention/working memory (PWH least square mean [LSM] = 50.4 vs controls LSM = 53.1, p = 0.008) and motor function (44.6 vs 47.7, p = 0.009) and a test of information processing speed (symbol search 30.3 vs 32.2, p = 0.003). They were more likely to self-report a higher number of cognitive difficulties in everyday life (p = 0.011). PWH also reported more depressive symptoms, general anxiety, and use of psychiatric medications (all with p < 0.05). PWH had reduced proportions of subcortical gray matter on MRI (β = -0.001, p < 0.001), and CSF showed elevated levels of neurofilament light chain (664 vs 529 pg/mL, p = 0.01) and tumor necrosis factor α (0.229 vs 0.156 ng/mL, p = 0.0008).

DISCUSSION

PWH, despite effective ART for over a decade, displayed neurocognitive deficits and mood abnormalities. MRI and CSF analyses revealed reduced brain volume and signs of ongoing neuronal injury and neuroinflammation. As the already large proportion of virologically controlled PWH continues to grow, longitudinal studies should be conducted to elucidate the implications of cognitive, psychiatric, MRI, and CSF abnormalities in this group.

Dynamic impairment classification through arrayed comparisons

The multivariate normative comparison (MNC) method has been used for identifying cognitive impairment. When participants' cognitive brain domains are evaluated regularly, the longitudinal MNC (LMNC) has been introduced to correct for the intercorrelation among repeated assessments of multiple cognitive domains in the same participant. However, it may not be practical to wait until the end of study for diagnosis. For example, in participants of the Multicenter AIDS Cohort Study (MACS), cognitive functioning has been evaluated repeatedly for more than 35 years. Therefore, it is optimal to identify cognitive impairment at each assessment, while the family-wise error rate (FWER) is controlled with unknown number of assessments in future. In this work, we propose to use the difference of consecutive LMNC test statistics to construct independent tests. Frequency modeling can help predict how many assessments each participant will have, so Bonferroni-type correction can be easily adapted. A chi-squared test is used under the assumption of multivariate normality, and permutation test is proposed where this assumption is violated. We showed through simulation and the MACS data that our method controlled FWER below a predetermined level.

One size does not fit all: An individualized approach to understand heterogeneous cognitive performance in autistic adults

Cognitive performances of autistic people vary widely. Therefore, previous group-based comparisons on cognitive aging in autistic adults might have overlooked those autistic adults that are particularly vulnerable for cognitive decline. Multivariate normative comparisons (MNC) statistically assess individual cognitive differences on the entire cognitive profile. Cognitive deviancy as indicated by MNC accurately predicts future cognitive decline, and is therefore sensitive in detecting meaningful cognitive differences. The current study aimed to (1) investigate the applicability of MNC to assess cognitive performance in autism individually, and (2) understand heterogeneous cognitive performance in autistic adults. As pre-registered, we performed MNC in a sample of 254 non-autistic adults, and two independent samples of respectively 118, and 86 autistic adults (20-85 years, mean: 50 years). Cognitive performance was measured on 11 outcomes in six domains (verbal/visual memory, working memory, verbal fluency, Theory of Mind, and psychomotor speed). Using MNC, about twice as many autistic individuals had a deviant cognitive profile (i.e., deviated statistically from the multivariate normspace) as compared to non-autistic individuals. Importantly, most autistic individuals (>80%) did not have a deviant cognitive profile. Having a deviant profile was significantly associated with higher levels of psychological distress in autistic adults specifically, showing the clinical relevance of this method. Therefore, MNC seem a useful tool to individually detect meaningful cognitive differences in autism. These results are consistent with previous cognitive studies suggesting that most autistic adults show fairly similar cognitive profiles to non-autistic adults, yet highlight the necessity for approaches reflecting the heterogeneity observed in autistic people.

Legacy effect on neuropsychological function in HIV-infected men on combination antiretroviral therapy

OBJECTIVE

To determine whether combination antiretroviral therapy (cART) initiation alters the trajectory of cognitive performance in HIV+ men, and whether cognition prior to cART predicts postcART function.

DESIGN

Longitudinal cohort study. Multicenter AIDS Cohort Study.

METHODS

From an initial set of 3701 men with complete neuropsychological data, men with HIV infection were initially matched with men without infection on cognitive status, race, age, and timeline (T0 defined as cART initiation). Propensity score matching was then used to match pairs on depressive symptoms at T0, education, T0 cognitive scores, and recruitment cohort. There were 506 matched pairs of infected and uninfected men in the final analysis. Mixed effect models were constructed to analyze the trajectories of cognitive functions and to test the effect of cART and HIV on cognitive functions over time.

RESULTS

Performance in each cognitive domain did not change following the initiation of cART among HIV-infected men with prior impairment and was comparable to the performance of their matched uninfected men. However, among the infected men who were unimpaired prior to cART, motor function declined significantly faster than it did for uninfected controls.

CONCLUSIONS

Cognitive dysfunction is persistent in HIV-infected men and cART does not alter the trajectory of cognitive decline in men who were impaired prior to effective therapy. This suggests that current cognitive impairment in HIV+ men results from a legacy effect, and from factors other than the HIV itself. Furthermore, motor skills may be uniquely vulnerable to the virus, cART, or age-related co-morbidities.

Predicting occupational outcomes from neuropsychological test performance in older people with HIV

OBJECTIVE

The ability to work is amongst the top concerns of people living with well treated HIV. Cognitive impairment has been reported in many otherwise asymptomatic persons living with HIV and even mild impairment is associated with higher rates of occupational difficulties. There are several classification algorithms for HIV-associated neurocognitive disorder (HAND) as well as overall scoring methods available to summarize neuropsychological performance. We asked which method best explained work status and productivity.

DESIGN

Participants (N = 263) drawn from a longitudinal Canadian cohort underwent neuropsychological testing.

METHODS

: Several classification algorithms were applied to establish a HAND diagnosis and two summary measures (NPZ and Global Deficit Score) were computed. Self-reported work status and productivity was assessed at each study visit (four visits, 9 months apart). The association of work status with each diagnostic classification and summary measure was estimated using logistic regression. For those working, the value on the productivity scale was regressed within individuals over time, and the slopes were regressed on each neuropsychological outcome.

RESULTS

The application of different classification algorithms to the neuropsychological data resulted in rates of impairment that ranged from 28.5 to 78.7%. Being classified as impaired by any method was associated with a higher rate of unemployment. None of the diagnostic classifications or summary methods predicted productivity, at time of testing or over the following 36 months.

CONCLUSION

Neuropsychological diagnostic classifications and summary scores identified participants who were more likely to be unemployed, but none explained productivity. New methods of assessing cognition are required to inform optimal workforce engagement.

Multimodal neuroimaging markers of variation in cognitive ability in older HIV+ men

OBJECTIVE

This study used converging methods to examine the neural substrates of cognitive ability in middle-aged and older men with well-controlled HIV infection.

METHODS

Seventy-six HIV+ men on antiretroviral treatment completed an auditory oddball task and an inhibitory control (Simon) task while time-locked high-density EEG was acquired; 66 had usable EEG data from one or both tasks; structural MRI was available for 43. We investigated relationships between task-evoked EEG responses, cognitive ability and immunocompromise. We also explored the structural correlates of these EEG markers in the sub-sample with complete EEG and MRI data (N = 27).

RESULTS

EEG activity was associated with cognitive ability at later (P300) but not earlier stages of both tasks. Only the oddball task P300 was reliably associated with HIV severity (nadir CD4). Source localization confirmed that the tasks engaged partially distinct circuits. Thalamus volume correlated with oddball task P300 amplitude, while globus pallidus volume was related to the P300 in both tasks.

INTERPRETATION

This is the first study to use task-evoked EEG to identify neural correlates of individual differences in cognition in men living with well-controlled HIV infection, and to explore the structural basis of the EEG markers. We found that EEG responses evoked by the oddball task are more reliably related to cognitive performance than those evoked by the Simon task. We also provide preliminary evidence for a subcortical contribution to the effects of HIV infection severity on P300 amplitudes. These results suggest brain mechanisms and candidate biomarkers for individual differences in cognition in HIV.

Rates of cognitive impairment in a South African cohort of people with HIV: variation by definitional criteria and lack of association with neuroimaging biomarkers

There is wide variation in the reported prevalence of cognitive impairment in people with HIV (PWH). Part of this variation may be attributable to different studies using different methods of combining neuropsychological test scores to classify participants as either cognitively impaired or unimpaired. Our aim was to determine, in a South African cohort of PWH (N = 148), (a) how much variation in reported rates was due to method used to define cognitive impairment and (b) which method correlated best with MRI biomarkers of HIV-related brain pathology. Participants completed detailed neuropsychological assessment and underwent 3 T structural MRI and diffusion tensor imaging (DTI). We used the neuropsychological data to investigate 20 different methods of determining HIV-associated cognitive impairment. We used the neuroimaging data to obtain volumes for cortical and subcortical grey matter and total white matter and DTI metrics for several white matter tracts. Applying each of the 20 methods to the cognitive dataset resulted in a wide variation (20-97%) in estimated rates of impairment. Logistic regression models showed no method was associated with HIV-related neuroimaging abnormalities as measured by structural volumes or DTI metrics. We conclude that for the population from which this sample was drawn, much of the variation in reported rates of cognitive impairment in PWH is due to the method of classification used, and that none of these methods accurately reflects biological effects of HIV in the brain. We suggest that defining HIV-associated cognitive impairment using neuropsychological test performance only is insufficient; pre-morbid functioning, co-morbidities, cognitive symptoms, and functional impairment should always be considered.

Reductions in Gray Matter Linked to Epigenetic HIV-Associated Accelerated Aging

A growing literature suggests a relationship between HIV-infection and a molecular profile of age acceleration. However, despite the widely known high prevalence of HIV-related brain atrophy and HIV-associated neurocognitive disorder (HAND), epigenetic age acceleration has not been linked to HIV-related changes in structural MRI. We applied morphological MRI methods to study the brain structure of 110 virally suppressed participants with HIV infection and 122 uninfected controls age 22-72. All participants were assessed for cognitive impairment, and blood samples were collected from a subset of 86 participants with HIV and 83 controls to estimate epigenetic age. We examined the group-level interactive effects of HIV and chronological age and then used individual estimations of epigenetic age to understand the relationship between age acceleration and brain structure. Finally, we studied the effects of HAND. HIV-infection was related to gray matter reductions, independent of age. However, using epigenetic age as a biomarker for age acceleration, individual HIV-related age acceleration was associated with reductions in total gray matter. HAND was associated with decreases in thalamic and hippocampal gray matter. In conclusion, despite viral suppression, accentuated gray matter loss is evident with HIV-infection, and greater biological age acceleration specifically relates to such gray matter loss.

Emerging Role of Nef in the Development of HIV Associated Neurological Disorders

Despite adherence to treatment, individuals living with HIV have an increased risk for developing cognitive impairments, referred to as HIV-associated neurological disorders (HAND). Due to continued growth in the HIV population, particularly amongst the aging cohort, the neurobiological mechanisms of HAND are increasingly relevant. Similar to other viral proteins (e.g. Tat, Gp120, Vpr), the Negative Factor (Nef) is associated with numerous adverse effects in the CNS as well as cognitive impairments. In particular, emerging data indicate the consequences of Nef may be facilitated by the modulation of cellular autophagy as well as its inclusion into extracellular vesicles (EVs). The present review examines evidence for the molecular mechanisms by which Nef might contribute to neuronal dysfunction underlying HAND, with a specific focus on autophagy and EVs. Based on the these data, we propose an integrated model by which Nef may contribute to underlying neuronal dysfunction in HAND and highlight potentially novel therapeutic targets for HAND. Graphical abstract.

Longitudinal 5-year prediction of cognitive impairment among men with HIV disease

BACKGROUND

Although combination antiretroviral therapy reduced the prevalence of HIV-associated dementia, milder syndromes persist. Our goals were to predict cognitive impairment of the Multicenter AIDS Cohort Study (MACS) participants 5 years ahead and from a large pool of factors, select the ones that mostly contributed to our predictions.

DESIGN

Longitudinal, natural and treated history of HIV infection among MSM.

METHODS

The MACS is a longitudinal study of the natural and treated history of HIV disease in MSM; the neuropsychological substudy aims to characterize cognitive disorders in men with HIV disease.

RESULTS

We modeled on an annual basis the risk of cognitive impairment 5 years in the future. We were able to predict cognitive impairment at individual level with high precision and overperform default methods. We found that while a diagnosis of AIDS is a critical risk factor, HIV infection per se does not necessarily convey additional risk. Other infectious processes, most notably hepatitis B and C, are independently associated with increased risk of impairment. The relative importance of an AIDS diagnosis diminished across calendar time.

CONCLUSION

Our prediction models are a powerful tool to help clinicians address dementia in early stages for MACS paticipants. The strongest predictors of future cognitive impairment included the presence of clinical AIDS and hepatitis B or C infection. The fact that the pattern of predictive power differs by calendar year suggests a clinically critical change to the face of the epidemic.

Chronic pain and cognitive impairment: a cross-sectional study in people living with HIV

Cognitive impairment and chronic pain are amongst the most prevalent neurological sequelae of HIV infection, yet little is understood about the potential bidirectional relationship between the two conditions. Cognitive dysfunction can occur in chronic pain populations whilst those with cognitive impairment can display modified responses to experimentally induced painful stimuli. To date, this has not been explored in HIV cohorts.This study aimed to identify any contribution of chronic pain to cognitive impairment in HIV and to determine differences in pain characteristics between those with and without cognitive dysfunction.This was an observational cohort study involving people living with HIV (n = 148) in the United Kingdom. Participants underwent validated questionnaire-based measurement of pain severity, interference and symptom quality as well as conditioned pain modulation and quantitative sensory testing. All participants completed a computer-based cognitive function assessment.Fifty-seven participants met the criteria for cognitive impairment and 73 for chronic pain. The cognitive impairment group had a higher prevalence of chronic pain (p = 0.004) and reported more neuropathic symptoms (p = 0.001). Those with chronic pain performed less well in emotional recognition and verbal learning domains. The interaction identified between chronic pain and cognitive dysfunction warrants further exploration to identify causal links or shared pathology.

Longitudinal multivariate normative comparisons

Motivated by the Multicenter AIDS Cohort Study (MACS), we develop classification procedures for cognitive impairment based on longitudinal measures. To control family-wise error, we adapt the cross-sectional multivariate normative comparisons (MNC) method to the longitudinal setting. The cross-sectional MNC was proposed to control family-wise error by measuring the distance between multiple domain scores of a participant and the norms of healthy controls and specifically accounting for intercorrelations among all domain scores. However, in a longitudinal setting where domain scores are recorded multiple times, applying the cross-sectional MNC at each visit will still have inflated family-wise error rate due to multiple testing over repeated visits. Thus, we propose longitudinal MNC procedures that are constructed based on multivariate mixed effects models. A χ 2 test procedure is adapted from the cross-sectional MNC to classify impairment on longitudinal multivariate normal data. Meanwhile, a permutation procedure is proposed to handle skewed data. Through simulations we show that our methods can effectively control family-wise error at a predetermined level. A dataset from a neuropsychological substudy of the MACS is used to illustrate the applications of our proposed classification procedures.

Neurocognitive Development in Perinatally Human Immunodeficiency Virus-infected Adolescents on Long-term Treatment, Compared to Healthy Matched Controls: A Longitudinal Study

BACKGROUND

A cross-sectional analysis of the Neurological, cOgnitive and VIsual performance in hiv-infected Children cohort showed significant cognitive impairment in combination antiretroviral therapy (cART)-treated, perinatally human immunodeficiency virus (HIV)-infected adolescents (PHIV+) compared to age-, sex-, ethnicity- and socioeconomic status (SES)-matched HIV-negative controls (HIV-). In this longitudinal study, we compared cognitive development in the same adolescents over time.

METHODS

We repeated the standardized cognitive test battery after a mean of 4.6 years (standard deviation 0.3). In participants who completed both assessments, we compared cognitive trajectories between groups in the domains of intelligence quotient (IQ), processing speed, working memory, executive functioning, learning ability, and visual-motor function, using linear mixed models. We explored associations with disease- and treatment-related factors and used multivariate normative comparison (MNC) to determine the prevalence of cognitive impairment.

RESULTS

There were 21 PHIV+ and 23 HIV- participants that completed 2 assessments and were similar concerning age, sex, ethnicity, and SES. Compared to HIV- participants, in PHIV+ participants the IQ score increased significantly more over time (group*time 6.01, 95% confidence interval [CI] 1.5-10.50; P = .012), whereas executive functioning decreased significantly more (group*time -1.43 z score, 95% CI -2.12 to -0.75; P < .001), resulting in the disappearance and appearance of significant differences. Processing speed, working memory, learning ability, and visual-motor function trajectories were not statistically different between groups. Univariately, those who had started cART at an older age deviated more in executive functioning (-0.13 z score, 95% CI -0.24 to -0.02; P = .043). The prevalence of cognitive impairments by MNC was similar in both groups, at both time points.

CONCLUSIONS

The cART-treated PHIV+ adolescents appeared to have similar global cognitive development, compared to their healthy peers. Executive functioning trajectory appears to deviate, potentially explained by earlier brain damage.

Studying the neuropsychological sequelae of SARS-CoV-2: lessons learned from 35 years of neuroHIV research

The virology of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and the human immune response to the virus are under vigorous investigation. There are now several reports describing neurological symptoms in individuals who develop coronavirus disease 2019 (COVID-19), the syndrome associated with SARS-CoV-2 infection. The prevalence, incidence, and clinical course of these symptoms will become clearer in the coming months and years through epidemiological studies. However, the long-term neurological and cognitive consequence of SARS-CoV-2 infection will remain conjectural for some time and will likely require the creation of cohort studies that include uninfected individuals. Considering the early evidence for neurological involvement in COVID-19 it may prove helpful to compare SARS-CoV-2 with another endemic and neurovirulent virus, human immunodeficiency virus-1 (HIV-1), when designing such cohort studies and when making predictions about neuropsychological outcomes. In this paper, similarities and differences between SARS-CoV-2 and HIV-1 are reviewed, including routes of neuroinvasion, putative mechanisms of neurovirulence, and factors involved in possible long-term neuropsychological sequelae. Application of the knowledge gained from over three decades of neuroHIV research is discussed, with a focus on alerting researchers and clinicians to the challenges in determining the cause of neurocognitive deficits among long-term survivors.

An Operational Definition of 'Abnormal Cognition' to Optimize the Prediction of Progression to Dementia: What Are Optimal Cut-Off Points for Univariate and Multivariate Normative Comparisons?

Background:

In neuropsychology and neurology, there is no consensus on the definition of abnormal cognition.

Objective:

To operationally define ‘abnormal cognition’ for optimally predicting progression to dementia in a memory clinic sample, and to test whether multivariate profile analysis of cognitive test results improves this prediction compared to standard clinical evaluation.

Methods:

We used longitudinal data from 835 non-demented patients of the Amsterdam Dementia Cohort. For 10 cognitive measures at baseline, we determined which number of abnormal tests and which magnitude of score deviations best predicted progression.

Results:

Predictive ability for progression to dementia of one, two, and three abnormal test scores out of 10 is highly similar (Cox hazard ratios: 3.7–4.1) provided cut-off values are adapted appropriately. Cut-offs have to be less stringent if the number of abnormal tests required increases: the optimal cut-off is z < –1.45 when one deviating score is required, z < –1.15 when two abnormal tests are required, and z < –0.70 when three abnormal tests are required. The profile analysis has similar predictive ability at the cut-off of p < 0.22 (hazard ratio 3.8). A likelihood ratio test showed that this analysis improves prediction of progression to dementia when added to standard clinical evaluation (p < 0.001).

Conclusion:

Abnormal cognition may be defined as one, two, or three abnormal test scores out of 10 if the magnitude of score deviations is adapted accordingly. An abnormal score profile predicts decline to dementia equally well, and improves the prediction when used complimentary to standard clinical evaluation.

Global prevalence and burden of HIV-associated neurocognitive disorder

Objective

To characterize the prevalence and burden of HIV-associated neurocognitive disorder (HAND) and assess associated factors in the global population with HIV.

Methods

We searched PubMed and Embase for cross-sectional or cohort studies reporting the prevalence of HAND or its subtypes in HIV-infected adult populations from January 1, 1996, to May 15, 2020, without language restrictions. Two reviewers independently undertook the study selection, data extraction, and quality assessment. We estimated pooled prevalence of HAND by a random effects model and evaluated its overall burden worldwide.

Results

Of 5,588 records identified, we included 123 studies involving 35,513 participants from 32 countries. The overall prevalence of HAND was 42.6% (95% confidence interval [CI] 39.7–45.5) and did not differ with respect to diagnostic criteria used. The prevalence of asymptomatic neurocognitive impairment, mild neurocognitive disorder, and HIV-associated dementia were 23.5% (20.3–26.8), 13.3% (10.6–16.3), and 5.0% (3.5–6.8) according to the Frascati criteria, respectively. The prevalence of HAND was significantly associated with the level of CD4 nadir, with a prevalence of HAND higher in low CD4 nadir groups (mean/median CD4 nadir <200 45.2% [40.5–49.9]) vs the high CD4 nadir group (mean/median CD4 nadir ≥200 37.1% [32.7–41.7]). Worldwide, we estimated that there were roughly 16,145,400 (95% CI 15,046,300–17,244,500) cases of HAND in HIV-infected adults, with 72% in sub-Saharan Africa (11,571,200 cases, 95% CI 9,600,000–13,568,000).

Conclusions

Our findings suggest that people living with HIV have a high burden of HAND in the antiretroviral therapy (ART) era, especially in sub-Saharan Africa and Latin America. Earlier initiation of ART and sustained adherence to maintain a high-level CD4 cell count and prevent severe immunosuppression is likely to reduce the prevalence and severity of HAND.

Development of a computerised neurocognitive battery for children and adolescents with HIV in Botswana: study design and protocol for the Ntemoga study

INTRODUCTION

Neurodevelopmental delays and cognitive impairments are common in youth living with HIV. Unfortunately, in resource-limited settings, where HIV infection impacts millions of children, cognitive and neurodevelopmental disorders commonly go undetected because of a lack of appropriate assessment instruments and local expertise. Here, we present a protocol to culturally adapt and validate the Penn Computerized Neurocognitive Battery (PennCNB) and examine its validity for detecting both advanced and subtle neurodevelopmental problems among school-aged children affected by HIV in resource-limited settings.

METHODS AND ANALYSIS

This is a prospective, observational cohort study. The venue for this study is Gaborone, Botswana, a resource-limited setting with high rates of perinatal exposure to HIV and limited neurocognitive assessment tools and expertise. We aim to validate the PennCNB in this setting by culturally adapting and then administering the adapted version of the battery to 200 HIV-infected, 200 HIV-exposed uninfected and 240 HIV-unexposed uninfected children. A series of analyses will be conducted to examine the reliability and construct validity of the PennCNB in these populations.

ETHICS AND DISSEMINATION

This project received ethical approval from local and university Institutional Review Boards and involved extensive input from local stakeholders. If successful, the proposed tools will provide practical screening and streamlined, comprehensive assessments that could be implemented in resource-limited settings to identify children with cognitive deficits within programmes focused on the care and treatment of children affected by HIV. The utility of such assessments could also extend beyond children affected by HIV, increasing general access to paediatric cognitive assessments in resource-limited settings.

Lower IQ and poorer cognitive profiles in treated perinatally HIV-infected children is irrespective of having a background of international adoption

Background

HIV-associated cognitive deficiency in perinatally HIV-infected (PHIV) children has been studied in Western countries in a population of which an increasing proportion has been internationally adopted. Studies often lack an appropriate internationally adopted HIV-uninfected control group, potentially confounding the relationship between HIV and cognitive functioning. This study aims to further elucidate the association between treated HIV infection and cognitive development by addressing the background of international adoption.

Methods

We cross-sectionally studied the impact of HIV on cognition by comparing PHIV children and HIV- uninfected controls, matched for age-, sex-, ethnicity-, socioeconomic status (SES)- and adoption status. We used a standardized neuropsychological test battery to measure intelligence (IQ), and the cognitive domains of processing speed, working memory, executive function, learning ability and visual-motor function and compared outcomes using lineair regression models, adjusted for IQ. We determined cognitive profiles and cognitive impairment by using multivariate normative comparison (MNC) and explored associations with HIV disease- and treatment-related factors.

Results

We enrolled fourteen PHIV children (mean age 10.45 years [1.73 SD], 93% adopted from sub-Saharan Africa at a median age of 3.3 years [IQR 2.1–4.2]) and fifteen HIV- uninfected controls. Groups did not clinically nor statistically differ in age, sex, ethnicity, SES, region of birth, adoption status and age at adoption. PHIV scored consistently lower on all cognitive domains and MNC outcomes. Compared to controls, PHIV children had a significant lower IQ (mean 81 [SD 11] versus mean 97 [SD 15], p = 0.005), and a poorer cognitive profile by MNC (Hotelling’s T² mean -4.36 [SD 5.6] versus mean 0.16 [SD 4.5], p = 0.021), not associated with HIV disease- and treatment-related factors. Two PHIV (14%) and one control (7%) were classified as cognitively impaired (p = 0.598).

Conclusions

Findings indicate treated HIV-infection to be independently associated with lower IQ and poorer cognitive profiles in PHIV children, irrespective of a background of international adoption.

Cognitive function and drivers of cognitive impairment in a European and a Korean cohort of people living with HIV

Although cognitive impairments are still prevalent in the current antiretroviral therapy era, limited investigations have compared the prevalence of cognitive disorder in people living with HIV (PLWH) and its determinants in different regions and ethnicities. We compared cognitive performance across six domains using comparable batteries in 134 PLWH aged ≥45 years from the COBRA study (Netherlands, UK), and 194 PLWH aged ≥18 years from the NeuroAIDS Project (South Korea). Cognitive scores were standardized and averaged to obtain domain and global T-scores. Associations with global T-scores were evaluated using multivariable regression and the ability of individual tests to detect cognitive impairment (global T-score ≤45) was assessed using the area-under-the-receiver-operating-characteristic curve (AUROC). The median (interquartile range) age of participants was 56 (51, 62) years in COBRA (88% white ethnicity, 93% male) and 45 (37, 52) years in NeuroAIDS (100% Korean ethnicity, 94% male). The rate of cognitive impairment was 18.8% and 18.0%, respectively ( p = 0.86). In COBRA, Black-African ethnicity was the factor most strongly associated with cognitive function (11.1 [7.7, 14.5] lower scores vs. white ethnicity, p < 0.01), whereas in NeuroAIDS, age (0.6 [0.1, 1.3] per 10-year, p<0.01) and education (0.7 [0.5, 0.9] per year, p<0.01) were significantly associated with cognitive function with anemia showing only a weak association (−1.2 [−2.6, 0.3], p=0.12). Cognitive domains most associated with cognitive impairment were attention (AUROC = 0.86) and executive function (AUROC = 0.87) in COBRA and processing speed (AUROC = 0.80), motor function (AUROC = 0.78) and language (AUROC = 0.78) in NeuroAIDS. Two cohorts of PLWH from different geographical regions report similar rates of cognitive impairment but different risk factors and cognitive profiles of impairment.

Cross-sectional analysis of cognitive function using multivariate normative comparisons in men with HIV disease

BACKGROUND

Prevalence estimates of cognitive impairment in HIV disease vary widely. Here we used multivariate normative comparison (MNC) with identify individuals with impaired cognition, and to compare the results with those using the Frascati and Gisslén criteria.

METHODS

The current project used data collected before October 2014 from bisexual/gay men from the Multicenter AIDS Cohort Study. A total of 2904 men (mean age 39.7 years, 52.7% seropositive) had complete data in six cognitive domains at their first neuropsychological evaluation. T-scores were computed for each domain and the MNC was applied to detect impairment among seronegative and seropositive groups.

RESULTS

The MNC classified 6.26% of seronegative men as being impaired using a predetermined 5% false discovery rate. By contrast, the Frascati and the Gisslén criteria identified 24.54 and 11.36% of seronegative men as impaired. For seropositive men, the percentage impairment was 7.45, 25.73, and 11.69%, respectively, by the MNC, Frascati and Gisslén criteria. When we used seronegative men without medical comorbidities as the control group, the MNC, the Frascati and the Gisslén criteria identified 5.05, 27.07, and 4.21% of the seronegative men, and 4.34, 30.95, and 4.48% of the seropositive men as having cognitive impairment. For each method, serostatus was not associated with cognitive impairment.

CONCLUSION

The MNC controls the false discovery rate and therefore avoids the low specificity that characterizes the Frascati and Gisslén criteria. More research is needed to evaluate the sensitivity of the MNC method in a seropositive population that may be sicker and older than the current study sample and that includes women.

Machine learning models reveal neurocognitive impairment type and prevalence are associated with distinct variables in HIV/AIDS

Neurocognitive impairment (NCI) among HIV-infected patients is heterogeneous in its reported presentations and frequencies. To determine the prevalence of NCI and its associated subtypes as well as predictive variables, we investigated patients with HIV/AIDS receiving universal health care. Recruited adult HIV-infected subjects underwent a neuropsychological (NP) test battery with established normative (sex-, age-, and education-matched) values together with assessment of their demographic and clinical variables. Three patient groups were identified including neurocognitively normal (NN, n = 246), HIV-associated neurocognitive disorders (HAND, n = 78), and neurocognitively impaired-other disorders (NCI-OD, n = 46). Univariate, multiple logistic regression and machine learning analyses were applied. Univariate analyses showed variables differed significantly between groups including birth continent, quality of life, substance use, and PHQ-9. Multiple logistic regression models revealed groups again differed significantly for substance use, PHQ-9 score, VACS index, and head injury. Random forest (RF) models disclosed that classification algorithms distinguished HAND from NN and NCI-OD from NN with area under the curve (AUC) values of 0.87 and 0.77, respectively. Relative importance plots derived from the RF model exhibited distinct variable rankings that were predictive of NCI status for both NN versus HAND and NN versus NCI-OD comparisons. Thus, NCI was frequently detected (33.5%) although HAND prevalence (21%) was lower than in several earlier reports underscoring the potential contribution of other factors to NCI. Machine learning models uncovered variables related to individual NCI types that were not identified by univariate or multiple logistic regression analyses, highlighting the value of other approaches to understanding NCI in HIV/AIDS.

Predicting Progression to Parkinson's Disease Dementia Using Multivariate Normative Comparisons

OBJECTIVE

Parkinson's disease with mild cognitive impairment (PD-MCI) is a risk factor for progression to PD dementia (PDD) at a later stage of the disease. The consensus criteria of PD-MCI use a traditional test-by-test normative comparison. The aim of this study was to investigate whether a new multivariate statistical method provides a more sensitive tool for predicting dementia status at 3- and 5-year follow-ups. This method allows a formal evaluation of a patient's profile of test scores given a large aggregated database with regression-based norms.

METHOD

The cognitive test results of 123 newly diagnosed PD patients from a previously published longitudinal study were analyzed with three different methods. First, the PD-MCI criteria were applied in the traditional way. Second, the PD-MCI criteria were applied using the large aggregated normative database. Last, multivariate normative comparisons (MNCs) were made using the same aggregated normative database. The outcome variable was progression to dementia within 3 and 5 years.

RESULTS

The MNC was characterized by higher sensitivity and higher specificity in predicting progression to PDD at follow-up than the two PD-MCI criteria methods, although the difference in classification accuracy did not reach statistical significance.

CONCLUSION

We conclude that MNCs could allow for a more accurate prediction of PDD than the traditional PD-MCI criteria, because there are encouraging trends in both increased sensitivity and increased specificity. (JINS, 2019, 25, 678-687).

Altered neuropsychological performance and reduced brain volumetrics in people living with HIV on integrase strand transfer inhibitors

OBJECTIVES

Neuropsychiatric symptoms have been reported in people living with HIV (PLWH) on integrase strand transfer inhibitors (INSTIs) in postmarketing analysis. Limited data exist regarding brain integrity (function and structure) in PLWH prescribed INSTIs compared with other HIV treatment regimens.

DESIGN

A cross-sectional analysis of PLWH on combined antiretroviral therapy aged more than 18 years at a single institution.

METHODS

Neuropsychological tests were administered to calculate domain deficit scores in learning/memory, executive function and motor/psychomotor domains. Cortical and subcortical volumes from MRI were obtained using the FreeSurfer software suite (v5.3).

RESULTS

Of 202 participants, median age 55 (48, 60) years old, 49% were on INSTI-based combined antiretroviral therapy. PLWH on INSTIs were similar to individuals on non-INSTIs in terms of age, sex, race, education years, smoking history, depression scores, psychiatric medication use, presence of hepatitis C infection, history of substance use, HIV infection duration and recent or nadir CD4 T-cell count. Participants in the INSTI group performed worse than non-INSTI users in the verbal learning and memory domain [1.5 (interquartile range 0, 2.5) versus 1 (0, 2); P = 0.016]. The INSTI and non-INSTI groups were similar for other cognitive domains. Frontal, brain stem and cerebellar volumes were reduced in INSTI compared with non-INSTI users (all P = <0.05).

CONCLUSION

We demonstrated modest differences in learning/memory performance and smaller brain volumes in PLWH on INSTI-based regimens compared with non-INSTI users. Prospective studies are needed to define mechanisms and the clinical significance of reduced brain integrity in PLWH on INSTIs.

Clinical and neuroimaging correlates of cognition in HIV

This study investigated whether HIV-positive participants, stable on combined antiretroviral therapy (cART), showed cognitive impairments relative to HIV-negative controls; and whether clinical and neuroimaging factors correlated with cognitive function in the HIV-positive participants. One hundred and twenty-six white men who have sex with men, of whom 78 were HIV-positive and stable on cART and 48 were HIV negative, were recruited to this cross-sectional study. The median age of HIV-positive participants in this study was 47. They underwent clinical and neuropsychological evaluation and magnetic resonance imaging of the brain, including diffusion tensor imaging (DTI). Cognitive scores for both groups were compared, and regression models were run to explore the influence of clinical, psychiatric, lifestyle, and neuroimaging variables on cognition. The prevalence of neurocognitive impairment, using the multivariate normative comparison criteria, was 28% in HIV-positive participants and 5% in HIV-negative participants. After covarying for age, years of education, and non-English speaking background, there were significant differences between the HIV group and the controls across four cognitive domains. The HIV group showed significantly higher mean diffusivity (MD) and lower fractional anisotropy (FA) than the control group on DTI. Although anxiety levels were clinically low, anxiety and DTI measures were the only variables to show significant correlations with cognitive function. In the HIV group, poorer cognitive performance was associated with higher MD and lower FA on DTI and higher (albeit clinically mild) levels of anxiety. Our findings suggest that white matter changes and subtle anxiety levels contribute independently to cognitive impairment in HIV.

Validation of a Novel Multivariate Method of Defining HIV-Associated Cognitive Impairment

BACKGROUND

The optimum method of defining cognitive impairment in virally suppressed people living with HIV is unknown. We evaluated the relationships between cognitive impairment, including using a novel multivariate method (NMM), patient- reported outcome measures (PROMs), and neuroimaging markers of brain structure across 3 cohorts.

METHODS

Differences in the prevalence of cognitive impairment, PROMs, and neuroimaging data from the COBRA, CHARTER, and POPPY cohorts (total n = 908) were determined between HIV-positive participants with and without cognitive impairment defined using the HIV-associated neurocognitive disorders (HAND), global deficit score (GDS), and NMM criteria.

RESULTS

The prevalence of cognitive impairment varied by up to 27% between methods used to define impairment (eg, 48% for HAND vs 21% for NMM in the CHARTER study). Associations between objective cognitive impairment and subjective cognitive complaints generally were weak. Physical and mental health summary scores (SF-36) were lowest for NMM-defined impairment ( P < .05).There were no differences in brain volumes or cortical thickness between participants with and without cognitive impairment defined using the HAND and GDS measures. In contrast, those identified with cognitive impairment by the NMM had reduced mean cortical thickness in both hemispheres ( P < .05), as well as smaller brain volumes ( P < .01). The associations with measures of white matter microstructure and brain-predicted age generally were weaker.

CONCLUSION

Different methods of defining cognitive impairment identify different people with varying symptomatology and measures of brain injury. Overall, NMM-defined impairment was associated with most neuroimaging abnormalities and poorer self-reported health status. This may be due to the statistical advantage of using a multivariate approach.

Depression, lifestyle factors and cognitive function in people living with HIV and comparable HIV-negative controls

Objectives

We investigated whether differences in cognitive performance between people living with HIV (PLWH) and comparable HIV‐negative people were mediated or moderated by depressive symptoms and lifestyle factors.

Methods

A cross‐sectional study of 637 ‘older’ PLWH aged ≥ 50 years, 340 ‘younger’ PLWH aged < 50 years and 276 demographically matched HIV‐negative controls aged ≥ 50 years enrolled in the Pharmacokinetic and Clinical Observations in People over Fifty (POPPY) study was performed. Cognitive function was assessed using a computerized battery (CogState). Scores were standardized into Z‐scores [mean = 0; standard deviation (SD) = 1] and averaged to obtain a global Z‐score. Depressive symptoms were evaluated via the Patient Health Questionnaire (PHQ‐9). Differences between the three groups and the effects of depression, sociodemographic factors and lifestyle factors on cognitive performance were evaluated using median regression. All analyses accounted for age, gender, ethnicity and level of education.

Results

After adjustment for sociodemographic factors, older and younger PLWH had poorer overall cognitive scores than older HIV‐negative controls (P < 0.001 and P = 0.006, respectively). Moderate or severe depressive symptoms were more prevalent in both older (27%; P < 0.001) and younger (21%; P < 0.001) PLWH compared with controls (8%). Depressive symptoms (P < 0.001) and use of hashish (P = 0.01) were associated with lower cognitive function; alcohol consumption (P = 0.02) was associated with better cognitive scores. After further adjustment for these factors, the difference between older PLWH and HIV‐negative controls was no longer significant (P = 0.08), while that between younger PLWH and older HIV‐negative controls remained significant (P = 0.01).

Conclusions

Poorer cognitive performances in PLWH compared with HIV‐negative individuals were, in part, mediated by the greater prevalence of depressive symptoms and recreational drug use reported by PLWH.

Multivariate Pattern Analysis of Volumetric Neuroimaging Data and Its Relationship With Cognitive Function in Treated HIV Disease

BACKGROUND

Accurate prediction of longitudinal changes in cognitive function would potentially allow for targeted intervention in those at greatest risk of cognitive decline. We sought to build a multivariate model using volumetric neuroimaging data alone to accurately predict cognitive function.

METHODS

Volumetric T1-weighted neuroimaging data from virally suppressed HIV-positive individuals from the CHARTER cohort (n = 139) were segmented into gray and white matter and spatially normalized before entering into machine learning models. Prediction of cognitive function at baseline and longitudinally was determined using leave-one-out cross-validation. In addition, a multivariate model of brain aging was used to measure the deviation of apparent brain age from chronological age and assess its relationship with cognitive function.

RESULTS

Cognitive impairment, defined using the global deficit score, was present in 37.4%. However, it was generally mild and occurred more commonly in those with confounding comorbidities (P < 0.001). Although multivariate prediction of cognitive impairment as a dichotomous variable at baseline was poor (area under the receiver operator curve 0.59), prediction of the global T-score was better than a comparable linear model (adjusted R = 0.08, P < 0.01 vs. adjusted R = 0.01, P = 0.14). Accurate prediction of longitudinal changes in cognitive function was not possible (P = 0.82). Brain-predicted age exceeded chronological age by mean (95% confidence interval) 1.17 (-0.14 to 2.53) years but was greatest in those with confounding comorbidities [5.87 (1.74 to 9.99) years] and prior AIDS [3.03 (0.00 to 6.06) years].

CONCLUSION

Accurate prediction of cognitive impairment using multivariate models using only T1-weighted data was not achievable, which may reflect the small sample size, heterogeneity of the data, or that impairment was usually mild.

Resting-state subcortical functional connectivity in HIV-infected patients on long-term cART

Despite long-term successful treatment with cART, impairments in cognitive functioning are still being reported in HIV-infected patients. Since changes in cognitive function may be preceded by subtle changes in brain function, neuroimaging techniques, such as resting-state functional magnetic resonance imaging (rs-fMRI) have become useful tools in assessing HIV-associated abnormalities in the brain. The purpose of the current study was to examine the extent to which HIV infection in virologically suppressed patients is associated with disruptions in subcortical regions of the brain in comparison to a matched HIV-negative control group. The sample consisted of 72 patients and 39 controls included between January 2012 and January 2014. Resting state functional connectivity was determined between fourteen regions-of-interest (ROI): the left and right nucleus accumbens, amygdala, caudate nucleus, hippocampus, putamen, pallidum and thalamus. A Bayesian method was used to estimate resting-state functional connectivity, quantified in terms of partial correlations. Both groups showed the strongest partial correlations between the left and right caudate nucleus and the left and right thalamus. However, no differences between the HIV patients and controls were found between the posterior expected network densities (control network density = 0.26, SD = 0.05, patient network density = 0.26, SD = 0.04, p = 0.58). The results of the current study show that HIV does not affect subcortical connectivity in virologically controlled patients who are otherwise healthy.

Gray and White Matter Abnormalities in Treated Human Immunodeficiency Virus Disease and Their Relationship to Cognitive Function

Background

Long-term comorbidities such as cognitive impairment remain prevalent in otherwise effectively treated people living with human immunodeficiency virus (HIV). We investigate the relationship between cognitive impairment and brain structure in successfully treated patients using multimodal neuroimaging from the Comorbidity in Relation to AIDS (COBRA) cohort.

Methods

Cognitive function, brain tissue volumes, and white matter microstructure were assessed in 134 HIV-infected patients and 79 controls. All patients had suppressed plasma HIV RNA at cohort entry. In addition to comprehensive voxelwise analyses of volumetric and diffusion tensor imaging, we used an unsupervised machine learning approach to combine cognitive, diffusion, and volumetric data, taking advantage of the complementary information they provide.

Results

Compared to the highly comparable control group, cognitive function was impaired in 4 of the 6 cognitive domains tested (median global T-scores: 50.8 vs 54.2; P < .001). Patients had lower gray but not white matter volumes, observed principally in regions where structure generally did not correlate with cognitive function. Widespread abnormalities in white matter microstructure were also seen, including reduced fractional anisotropy with increased mean and radial diffusivity. In contrast to the gray matter, these diffusion abnormalities correlated with cognitive function. Multivariate neuroimaging analysis identified a neuroimaging phenotype associated with poorer cognitive function, HIV infection, and systemic immune activation.

Conclusions

Cognitive impairment, lower gray matter volume, and white matter microstructural abnormalities were evident in HIV-infected individuals despite fully suppressive antiretroviral therapy. White matter abnormalities appear to be a particularly important determinant of cognitive dysfunction seen in well-treated HIV-infected individuals.

Medicalising normality? Using a simulated dataset to assess the performance of different diagnostic criteria of HIV-associated cognitive impairment

Objective

The reported prevalence of cognitive impairment remains similar to that reported in the pre-antiretroviral therapy era. This may be partially artefactual due to the methods used to diagnose impairment. In this study, we evaluated the diagnostic performance of the HIV-associated neurocognitive disorder (Frascati criteria) and global deficit score (GDS) methods in comparison to a new, multivariate method of diagnosis.

Methods

Using a simulated ‘normative’ dataset informed by real-world cognitive data from the observational Pharmacokinetic and Clinical Observations in PeoPle Over fiftY (POPPY) cohort study, we evaluated the apparent prevalence of cognitive impairment using the Frascati and GDS definitions, as well as a novel multivariate method based on the Mahalanobis distance. We then quantified the diagnostic properties (including positive and negative predictive values and accuracy) of each method, using bootstrapping with 10,000 replicates, with a separate ‘test’ dataset to which a pre-defined proportion of ‘impaired’ individuals had been added.

Results

The simulated normative dataset demonstrated that up to ~26% of a normative control population would be diagnosed with cognitive impairment with the Frascati criteria and ~20% with the GDS. In contrast, the multivariate Mahalanobis distance method identified impairment in ~5%. Using the test dataset, diagnostic accuracy [95% confidence intervals] and positive predictive value (PPV) was best for the multivariate method vs. Frascati and GDS (accuracy: 92.8% [90.3–95.2%] vs. 76.1% [72.1–80.0%] and 80.6% [76.6–84.5%] respectively; PPV: 61.2% [48.3–72.2%] vs. 29.4% [22.2–36.8%] and 33.9% [25.6–42.3%] respectively). Increasing the a priori false positive rate for the multivariate Mahalanobis distance method from 5% to 15% resulted in an increase in sensitivity from 77.4% (64.5–89.4%) to 92.2% (83.3–100%) at a cost of specificity from 94.5% (92.8–95.2%) to 85.0% (81.2–88.5%).

Conclusion

Our simulations suggest that the commonly used diagnostic criteria of HIV-associated cognitive impairment label a significant proportion of a normative reference population as cognitively impaired, which will likely lead to a substantial over-estimate of the true proportion in a study population, due to their lower than expected specificity. These findings have important implications for clinical research regarding cognitive health in people living with HIV. More accurate methods of diagnosis should be implemented, with multivariate techniques offering a promising solution.

HIV-associated neurocognitive disorder

PURPOSE OF REVIEW

HIV-associated neurocognitive disease is the most active topic for neuroAIDS investigations at present. Although impairment is mild in patients successfully treated with modern antiviral regimens, it remains an ongoing problem for HIV patients. It is important to update the emerging research concerning HIV-associated neurocognitive disease.

RECENT FINDINGS

The virus enters the brain during acute infection, with evidence for abnormal functioning that may occur early and often persists. Direct relationships with ongoing viral infection continue to be monitored, but chronic inflammation often associated with monocytes and macrophages appears to be the most likely driver of cognitive dysfunction. Appreciation for cerebrovascular disease as a significant comorbidity that is associated with cognitive deficits is increasing. Neuroimaging is actively being developed to address detection and measurement of changes in the brain. Optimal combined antiretroviral treatment therapy has vastly improved neurologic outcomes, but so far has not been demonstrated to reverse the remaining mild impairment. Inflammatory and vascular mechanisms of cerebral dysfunction may need to be addressed to achieve better outcomes.

SUMMARY

Ongoing research is required to improve neurological outcomes for persons living with HIV. It is likely that interventions beyond antiviral approaches will be required to control or reverse HIV-associated neurocognitive disease.

The Montreal Cognitive Assessment-Basic (MoCA-B) is not a reliable screening tool for cognitive decline in HIV patients receiving combination antiretroviral therapy in rural South Africa

BACKGROUND

HIV-associated neurocognitive disorders (HAND) are frequently occurring comorbidities in HIV-positive patients, diagnosed by means of a neuropsychological assessment (NPA). Due to the magnitude of the HIV-positive population in Sub-Saharan Africa, easy-to-use cognitive screening tools are essential.

METHODS

This was a cross-sectional clinical trial involving 44 HIV-positive patients (on stable cART) and 73 HIV-negative controls completing an NPA, the International HIV Dementia Scale (IHDS), and a culturally appropriate cognitive screening tool, the Montreal Cognitive Assessment-Basic (MoCA-B). HAND were diagnosed by calculating Z-scores using internationally published normative data on NPA, as well as by using data from the HIV-negative group to validate the MoCA-B.

RESULTS

One hundred and seventeen patients were included (25% male, median age 35 years, median 11 years of education). A moderate correlation was found between the MoCA-B and NPA total Z-score (Pearson's r=0.36, p=0.02). Area under the curve (AUC) values for MoCA-B and IHDS were 0.59 and 0.70, respectively. The prevalence of HAND in HIV-positive patients was 66% when calculating Z-scores using published normative data versus 48% when using the data from the present HIV-negative cohort.

CONCLUSION

The MoCA-B appeared not to be a valid screening tool for HAND in this setting. The prevalence of HAND in this setting is high, but appeared overestimated when using published norms.

HIV-Associated Neurocognitive Disorders: A Global Perspective

The present review on HIV-associated neurocognitive disorders (HAND) provides a worldwide overview of studies that have investigated the rate and neuropsychological (NP) profile of HAND research since the inception of the 2007 HAND diagnostic nomenclature. In the first part, the review highlights some of the current controversies around HAND prevalence rates. In the second part, the review critically assesses some solutions to move the field forward. In the third part, we present the cross-sectional NP profile in non-Western HIV+ cohorts and in relation to Western cohorts' findings. The adopted global perspective highlights the successful expansion of NP studies in HIV infection to culturally diverse low- to medium-income countries with high HIV burden. These studies have produced interestingly similar rates of HAND whether patients were naïve or treated and/or virally suppressed compared to the rich income countries where the NP research in NeuroHIV has originated. The perspective also demonstrates that globally, the group which is the most representative of the HIV epidemic, and thus at risk for HAND are persons with chronic HIV infection and survivors of past immunosuppression, while in relative terms, those who have been treated early with long-term viral suppression represent a minority. In the last part, we present a review of the naturalistic longitudinal NP global studies in HIV+cohorts, discuss the role of longitudinal design in solving issues around the question of asymptomatic neurocognitive impairment, and the question of biomarker discovery. Finally, we conclude by calling for greater methods and data harmonization at a global level. (JINS, 2017, 23, 860-869).

Predictors and Impact of Self-Reported Suboptimal Effort on Estimates of Prevalence of HIV-Associated Neurocognitive Disorders

BACKGROUND

Prevalence estimates of HIV-associated neurocognitive disorders (HAND) may be inflated. Estimates are determined via cohort studies in which participants may apply suboptimal effort on neurocognitive testing, thereby inflating estimates. Additionally, fluctuating HAND severity over time may be related to inconsistent effort. To address these hypotheses, we characterized effort in the Multicenter AIDS Cohort Study.

METHODS

After neurocognitive testing, 935 participants (525 HIV- and 410 HIV+) completed the visual analog effort scale (VAES), rating their effort from 0% to 100%. Those with <100% then indicated the reason(s) for suboptimal effort. K-means cluster analysis established 3 groups: high (mean = 97%), moderate (79%), and low effort (51%). Rates of HAND and other characteristics were compared between the groups. Linear regression examined the predictors of VAES score. Data from 57 participants who completed the VAES at 2 visits were analyzed to characterize the longitudinal relationship between effort and HAND severity.

RESULTS

Fifty-two percent of participants reported suboptimal effort (<100%), with no difference between serostatus groups. Common reasons included "tired" (43%) and "distracted" (36%). The lowest effort group had greater asymptomatic neurocognitive impairment and minor neurocognitive disorder diagnosis (25% and 33%) as compared with the moderate (23% and 15%) and the high (12% and 9%) effort groups. Predictors of suboptimal effort were self-reported memory impairment, African American race, and cocaine use. Change in effort between baseline and follow-up correlated with change in HAND severity.

CONCLUSIONS

Suboptimal effort seems to inflate estimated HAND prevalence and explain fluctuation of severity over time. A simple modification of study protocols to optimize effort is indicated by the results.

Measuring and managing cognitive impairment in HIV

: Cognitive impairment remains a frequently reported complaint in HIV-positive patients despite virologically suppressive antiretroviral therapy. Rates of cognitive impairment in antiretroviral treated HIV-positive cohorts vary and strongly depend on definitions utilized.The underlying pathogenesis is likely to be multifactorial and includes immune activation, neuroinflammation, antiretroviral neurotoxicity, the presence of noninfectious comorbidities such as vascular disease and depression and patient lifestyle factors such as recreational drug use.Contributing factors to cognitive impairment may change over time with ageing HIV-positive populations. Cerebrovascular disease and neurodegenerative causes of cognitive impairment may become more common with advancing age; how these factors interact with HIV-associated cognitive impairment is not yet known.Cerebrospinal fluid HIV RNA escape may occur in up to 10% of patients undergoing lumbar puncture clinically and can be associated with compartmentalized and resistant virus.Changes in antiretroviral therapy in patients with cognitive impairment should be based on current and historic resistance profiles of cerebrospinal fluid and plasma virus, or on potential antiretroviral drug neurotoxicity. Whether and how antiretroviral therapy should be changed in the absence of these factors is not known and requires study in adequately powered randomized trials in carefully selected clinical cohorts.

Cerebral blood flow and cognitive function in HIV-infected men with sustained suppressed viremia on combination antiretroviral therapy

OBJECTIVE

To assess if HIV-infected patients on long-term successful combination antiretroviral therapy show cerebral blood flow (CBF) alterations in comparison with HIV-uninfected, otherwise similar controls. To explore whether such alterations are associated with HIV-associated cognitive impairment and to explore potential determinants of CBF alterations in HIV.

DESIGN

Cross-sectional comparison of CBF in an observational cohort study.

METHODS

Clinical, cognitive and MRI data of 100 middle-aged aviremic HIV-infected men on combination antiretroviral therapy and 69 HIV-uninfected controls were collected and compared. From pseudocontinuous arterial spin labeling MRI data, CBF-maps were calculated. The associations of mean gray matter CBF with clinical and cognitive parameters were explored in regression models, followed by a spatial delineation in a voxel-based analysis.

RESULTS

CBF was decreased in HIV-infected patients compared with HIV-uninfected controls (P = 0.02), adjusted for age, ecstasy use and waist circumference. Spatially distinct and independent effects of total gray matter volume and HIV-serostatus on CBF were found. Within the HIV-infected group, decreased CBF was associated with increased triglyceride levels (P = 0.005) and prior clinical AIDS (P = 0.03). No association between CBF and cognitive impairment was found.

CONCLUSION

Decreased CBF was observed among HIV-infected patients, which was associated with both vascular risk factors as well as with measures of past immune deficiency. These results provide support for increased vascular disease in HIV-infected patients as represented by hemodynamic alteration, but without overt cognitive consequences within the current cohort of patients on long-term successful treatment.

Multivariate normative comparisons using an aggregated database

In multivariate normative comparisons, a patient’s profile of test scores is compared to those in a normative sample. Recently, it has been shown that these multivariate normative comparisons enhance the sensitivity of neuropsychological assessment. However, multivariate normative comparisons require multivariate normative data, which are often unavailable. In this paper, we show how a multivariate normative database can be constructed by combining healthy control group data from published neuropsychological studies. We show that three issues should be addressed to construct a multivariate normative database. First, the database may have a multilevel structure, with participants nested within studies. Second, not all tests are administered in every study, so many data may be missing. Third, a patient should be compared to controls of similar age, gender and educational background rather than to the entire normative sample. To address these issues, we propose a multilevel approach for multivariate normative comparisons that accounts for missing data and includes covariates for age, gender and educational background. Simulations show that this approach controls the number of false positives and has high sensitivity to detect genuine deviations from the norm. An empirical example is provided. Implications for other domains than neuropsychology are also discussed. To facilitate broader adoption of these methods, we provide code implementing the entire analysis in the open source software package R.

A comparison of the sensitivity, stability, and reliability of three diagnostic schemes for HIV-associated neurocognitive disorders

HIV-associated neurocognitive disorders (HAND) occur in approximately 50% of HIV-infected individuals, yet available diagnostic criteria yield varying prevalence rates. This study examined the frequency, reliability, and sensitivity to everyday functioning problems of three HAND diagnostic criteria (DSM-5, Frascati, Gisslén). Participants included 361 adults with HIV disease and 199 seronegative adults. Neurocognitive status as defined by each of the three diagnostic systems was determined via a comprehensive neuropsychological battery. Everyday functioning was evaluated through self-report and clinician ratings. Results of logistic regressions revealed an association of HIV serostatus with Frascati-defined neurocognitive impairment (p = .027, OR = 1.7[1.1, 2.7]), but not DSM-5 or Gisslén-defined criteria (ps > .05). Frascati and DSM-5 criteria demonstrated agreement on 71% of observations, Frascati and Gisslén showed agreement on 80%, and DSM-5 and Gisslén criteria showed agreement on 46%, though reliability across the three criteria was poor. Only Frascati-defined neurocognitive impairment significantly predicted everyday functioning problems (p = .002, OR = 2.3[1.4, 3.8]). However, when both neurocognitive and complaint criteria were considered, the DSM-5 guidelines demonstrated significant relationships to everyday functioning, serostatus, and also increased reliability overtime compared to neurocognitive criteria alone (all ps < .05). A subset (n = 118) of the HIV+ group was assessed again after 14.0 (2.2) months. DSM-5 criteria evidenced significantly higher rates of incident neurocognitive disorder compared to both Frascati (p = .003) and Gisslén (p = .021) guidelines, while there were fewer remitting neurocognitive disorder diagnoses when Gisslén criteria were applied to the study sample compared to Frascati (p = .04). Future studies should aim to identify gold standard biological markers (e.g., neuropathology) and clinical outcomes associated with specific diagnostic criteria.

Defining cognitive impairment in people-living-with-HIV: the POPPY study

Background

The reported prevalence of cognitive impairment (CI) varies widely in cohorts of people living with HIV (PLWH); this may partly be due to the use of different diagnostic criteria. Agreement between diagnostic criteria of CI, the optimal definition to use, and associations with patient-reported cognitive symptoms have not been fully investigated.

Methods

Two hundred ninety PLWH aged >50 years and 97 matched negative controls completed a detailed assessment of cognitive function and three questions regarding cognitive symptoms. Age- and education-adjusted test scores (T-scores) determined if subjects met the following definitions of CI: Frascati, global deficit score (GDS) and the multivariate normative comparison (MNC) method.

Results

PLWH were more likely than controls to meet each definition of CI (ORs were 2.17, 3.12 and 3.64 for Frascati, GDS and MNC, respectively). Agreement of MNC with Frascati and GDS was moderate (Cohen’s k = 0.42 and 0.48, respectively), whereas that between Frascati and GDS was good (k = 0.74). A significant association was found between all the three criteria and reporting of memory loss but not with attention and reasoning problems. The 41 (14 %) PLWH meeting all the three criteria had the lowest median global T-score (36.9) and highest rate of symptom reporting (42 %).

Conclusions

Different CI criteria show fair diagnostic agreement, likely reflecting their ability to exclude CI in the same group of individuals. Given the lower overall cognitive performance and higher rates of symptom reporting in those meeting all three criteria of CI, further work assessing this as a definition of CI in PLWH is justified.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1970-8) contains supplementary material, which is available to authorized users.

Associations between cognitive impairment and patient-reported measures of physical/mental functioning in older people living with HIV

OBJECTIVES

While cognitive impairment is frequently reported in HIV-positive individuals and has historically been associated with poorer functional outcomes, the associations between cognitive impairment and patient-reported outcome measures (PROMs) in contemporary cohorts are unclear.

METHODS

We tested cognitive function using a computerized battery (CogState^™ ) in 290 HIV-positive and 97 HIV-negative individuals aged ≥ 50 years participating in the Pharmacokinetic and Clinical Observations in People Over Fifty (POPPY) study. Participants completed questionnaires detailing physical and mental health [Short Form Health Survey (SF-36)], cognitive function [European AIDS Clinical Society (EACS) questions], activities of daily living [Lawton Instrumental Activities of Daily Living (IADL)], depression [Patient Depression Questionnaire (PHQ-9) and Centres for Epidemiologic Studies Depression scale (CES-D)], falls and sexual desire. Cognitive impairment was defined using the Frascati criteria, global deficit score (GDS) and multivariate normative comparison (MNC). In the HIV-positive group, the classification performances of the different definitions of cognitive impairment and dichotomized questionnaire results were calculated.

RESULTS

The prevalence of cognitive impairment in the HIV-positive group was 34.5% (GDS), 30.0% (Frascati) and 22.1% (MNC), with only 2% diagnosed with HIV-associated dementia. In general, the associations between cognitive impairment and PROMs were weak regardless of the definition used: mean c-statistics were 0.543 (GDS), 0.530 (MNC) and 0.519 (Frascati). Associations were similar using the global T-score to define cognitive impairment. Summary health scores (SF-36) were lower, but only significantly so for those with cognitive impairment identified using MNC, for both mental health (61.4 vs. 75.8; P = 0.03) and physical health (60.9 vs. 75.0; P = 0.03).

CONCLUSIONS

The associations between cognitive impairment and PROMs were weak, possibly because impairment was mild and therefore largely asymptomatic. Further work is needed to elucidate the clinical implications of cognitive impairment in HIV-disease.

Advanced Neuropsychological Diagnostics Infrastructure (ANDI): A Normative Database Created from Control Datasets

In the Advanced Neuropsychological Diagnostics Infrastructure (ANDI), datasets of several research groups are combined into a single database, containing scores on neuropsychological tests from healthy participants. For most popular neuropsychological tests the quantity, and range of these data surpasses that of traditional normative data, thereby enabling more accurate neuropsychological assessment. Because of the unique structure of the database, it facilitates normative comparison methods that were not feasible before, in particular those in which entire profiles of scores are evaluated. In this article, we describe the steps that were necessary to combine the separate datasets into a single database. These steps involve matching variables from multiple datasets, removing outlying values, determining the influence of demographic variables, and finding appropriate transformations to normality. Also, a brief description of the current contents of the ANDI database is given.

White matter hyperintensities in relation to cognition in HIV-infected men with sustained suppressed viral load on combination antiretroviral therapy

OBJECTIVES

The objective of this study was to assess whether HIV-infected patients on long-term successful combination antiretroviral therapy (cART) have more extensive white matter hyperintensities (WMH) of presumed vascular origin compared with uninfected controls and whether these intensities are associated with cognitive impairment. Furthermore, we explored potential determinants of increased WMH load long-term suppressed HIV infection.

DESIGN

A cross-sectional comparison of WMH in an observational cohort.

METHODS

Clinical, cognitive, and MRI data were collected from 103 middle-aged, aviremic HIV-infected men on cART, and 70 HIV-uninfected, otherwise similar controls. In the MRI data, WMH load was quantified by automated approaches and qualitatively reviewed by an experienced neuroradiologist using the Fazekas scale.

RESULTS

HIV-infected men had an increased WMH load. Among HIV-infected patients, increased WMH load was independently associated with older age, higher DBP, higher D-dimer levels, and longer time spent with a CD4 cell count below 500 cells/μl. HIV-associated cognitive deficits were associated with increased WMH load.

CONCLUSIONS

WMH are more extensive and associated with cognitive deficits in middle-aged, aviremic cART-treated HIV-infected men. The extent of WMH load was associated with both cardiovascular risk factors and past immune deficiency. As cognitive impairment in these same patients is also associated with these risk factors, this may suggest that in the setting of HIV, WMH, and cognitive deficits share a common cause. This supports the importance of optimizing cardiovascular risk management, and early, effective treatment of HIV infection.

Cognitive Function in Young Persons With and Without Perinatal HIV in the AALPHI Cohort in England: Role of Non-HIV-Related Factors

BACKGROUND

 There is limited evidence about the cognitive performance of older adolescents with perinatally acquired human immunodeficiency virus (HIV) compared with HIV-negative (HIV-) adolescents.

METHODS

 A total of 296 perinatally HIV-infected (PHIV+) and 97 HIV- adolescents (aged 12-21 and 13-23 years, respectively) completed 12 tests covering 6 cognitive domains. The HIV- participants had PHIV+ siblings and/or an HIV-infected mother. Domain-specific and overall (NPZ-6) z scores were calculated for PHIV+ participants, with or without Centers for Disease Control and Prevention (CDC) stage C disease, and HIV- participants. Linear regression was performed to explore predictors of NPZ-6.

RESULTS

 One hundred twenty-five (42%) of the PHIV+ and 31 (32%) of the HIV- participants were male; 251 (85%) and 69 (71%), respectively, were black African; and their median ages (interquartile range) were 16 (15-18) and 16 (14-18) years, respectively. In PHIV+ participants, 247 (86%) were receiving antiretroviral therapy, and 76 (26%) had a previous CDC C diagnosis. The mean (standard deviation) NPZ-6 score was -0.81 (0.99) in PHIV+ participants with a CDC C diagnosis (PHIV+/C), -0.45 (0.80) in those without a CDC C diagnosis (PHIV+/no C), and -0.32 (0.76) in HIV- participants (P < .001). After adjustment, there was no difference in NPZ-6 scores between PHIV+/no C and HIV- participants (adjusted coefficient, -0.01; 95% confidence interval, -.22 to .20). PHIV+/C participants scored below the HIV- group (adjusted coefficient, -0.44; -.70 to -.19). Older age predicted higher NPZ-6 scores, and black African ethnicity and worse depression predicted lower NPZ-6 scores. In a sensitivity analysis including PHIV+ participants only, no HIV-related factors apart from a CDC C diagnosis were associated with NPZ-6 scores.

CONCLUSIONS

 Cognitive performance was similar between PHIV+/no C and HIV- participants and indicated relatively mild impairment compared with normative data. The true impact on day-to-day functioning needs further investigation.

Associations Between Neurocognitive Impairment and Biomarkers of Poor Physiologic Reserve in a Clinic-Based Sample of Older Adults Living with HIV

Data from a cross-sectional study of a clinic-based sample of older people living with HIV (PLWH; n = 100) were used to examine associations between biomarkers of physical health and neurocognitive impairment (NCI). In this sample, anemia, chronic kidney disease (CKD) stages 4-5, and hypocalcemia were associated with impairment in executive functioning or processing speed. Furthermore, participants with anemia were more likely to have CD4+ T cell counts <200 cells/mm³ (χ² [1] = 19.57, p < .001); hypocalcemia (χ² [1] = 17.55, p < .001); and CKD 4-5 (χ² [2] = 10.12, p = .006). Black and Hispanic participants were more likely to be anemic compared to other races and ethnicities (χ² [3] = 12.76, p = .005). Common medical conditions (e.g., anemia, hypocalcemia, CKD) should be investigated as potential contributors to NCI in older PLWH. Additionally, laboratory testing in racial/ethnic minority PLWH may help inform NCI screening.

Neurocognitive Function and Neuroimaging Markers in Virologically Suppressed HIV-positive Patients Randomized to Ritonavir-boosted Protease Inhibitor Monotherapy or Standard Combination ART: A Cross-sectional Substudy From the PIVOT Trial

BACKGROUND

To determine whether treatment with ritonavir-boosted protease inhibitor (PI) monotherapy is associated with detrimental effects on neurocognitive function or brain imaging markers compared to standard antiretroviral therapy (ART).

METHODS

Neuropsychological assessment and brain magnetic resonance imaging were performed at the last study visit in a subset of participants randomized to PI monotherapy (PI-mono group) or ongoing triple ART (OT group) in the PIVOT trial. We calculated a global z-score (NPZ-7) from the average of the individual test z-scores and the proportion of participants with symptomatic neurocognitive impairment (score >1 standard deviation below normative means in ≥2 cognitive domains and neurocognitive symptoms). In a subgroup, white matter hyperintensities, bicaudate index, global cortical (GCA) and medial temporal lobe atrophy scores and single voxel (basal ganglia) N-acetylaspartate (NAA)/Choline, NAA/Creatine and myo-inositol/Creatine ratios were measured.

RESULTS

146 participants (75 PI-mono) had neurocognitive testing (median time after randomization 3.8 years), of whom 78 were imaged. We found no difference between arms in NPZ-7 score (median -0.4 (interquartile range [IQR] = -0.7; 0.1) vs -0.3 (IQR = -0.7; 0.3) for the PI-mono and OT groups respectively, P = .28), the proportion with symptomatic neurocognitive impairment (13% and 18% in the PI-mono and OT groups respectively; P = .41), or any of the neuroimaging variables (P > .05). Symptomatic neurocognitive impairment was associated with higher GCA score (OR = 6.2 per additional score; 95% confidence interval, 1.7-22.3 P = .005) but no other imaging variables.

CONCLUSIONS

Based on a comprehensive neuropsychological assessment and brain imaging, PI monotherapy does not increase the risk of neurocognitive impairment in stable human immunodeficiency virus-positive patients.