Disease burden in HIV-associated cognitive impairment: a study of whole-brain imaging measures

Multishell diffusion MRI reveals whole-brain white matter changes in HIV

Diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) have been previously used to explore white matter related to human immunodeficiency virus (HIV) infection. While DTI and DKI suffer from low specificity, the Combined Hindered and Restricted Model of Diffusion (CHARMED) provides additional microstructural specificity. We used these three models to evaluate microstructural differences between 35 HIV-positive patients without neurological impairment and 20 healthy controls who underwent diffusion-weighted imaging using three b-values. While significant group effects were found in all diffusion metrics, CHARMED and DKI analyses uncovered wider involvement (80% vs. 20%) of all white matter tracts in HIV infection compared with DTI. In restricted fraction (FR) analysis, we found significant differences in the left corticospinal tract, middle cerebellar peduncle, right inferior cerebellar peduncle, right corticospinal tract, splenium of the corpus callosum, left superior cerebellar peduncle, left superior cerebellar peduncle, pontine crossing tract, left posterior limb of the internal capsule, and left/right medial lemniscus. These are involved in language, motor, equilibrium, behavior, and proprioception, supporting the functional integration that is frequently impaired in HIV-positivity. Additionally, we employed a machine learning algorithm (XGBoost) to discriminate HIV-positive patients from healthy controls using DTI and CHARMED metrics on an ROIwise basis, and unique contributions to this discrimination were examined using Shapley Explanation values. The CHARMED and DKI estimates produced the best performance. Our results suggest that biophysical multishell imaging, combining additional sensitivity and built-in specificity, provides further information about the brain microstructural changes in multimodal areas involved in attentive, emotional and memory networks often impaired in HIV patients.

Validating 1-Year Reliable Change Methods

OBJECTIVE

reliable change methods can assist in the determination of whether observed changes in performance are meaningful. The current study sought to validate previously published 1-year standardized regression-based (SRB) equations for commonly administered neuropsychological measures that incorporated baseline performances, demographics, and 1-week practice effects.

METHOD

Duff et al.'s SRB prediction equations were applied to an independent sample of 70 community-dwelling older adults with either normal cognition or mild cognitive impairment, assessed at baseline, at 1 week, and at 1 year.

RESULTS

minimal improvements or declines were seen between observed baseline and observed 1-year follow-up scores, or between observed 1-year and predicted 1-year scores, on most measures. Relatedly, a high degree of predictive accuracy was observed between observed 1-year and predicted 1-year scores across cognitive measures in this repeated battery.

CONCLUSIONS

these results, which validate Duff et al.'s SRB equations, will permit clinicians and researchers to have more confidence when predicting cognitive performance on these measures over 1 year.

Effect of human immunodeficiency virus on the brain: A review

Thirty million people are infected with human immunodeficiency virus (HIV) worldwide, and HIV-associated neurocognitive disorder (HAND) is one of the most common comorbidities of HIV. However, the effect of HIV on the brain has not been fully investigated. This article aimed to review the changes to the brain due to HIV in terms of atrophy, diffusion changes, and hyperintensities. Studies have observed significant atrophy in subcortical gray matter, as well as in cortical white and gray matter. Moreover, the ventricles enlarge, and the sulci widen. Although HIV causes changes to the white and gray matter of the brain, few diffusion tensor imaging studies have investigated the changes to gray matter integrity. White and gray matter hyperintensities have frequently been observed in HIV-positive individuals, with the subcortical gray matter (caudate nucleus and putamen) and periventricular white matter frequently affected. In conclusion, subcortical gray matter is the first brain region to be affected and is affected most severely. Additionally, this review highlights the gaps in the literature, since the effect of HIV on the brain is not fully known. Future studies should continue to investigate the effect of HIV on the brain in different stages of the disease, and alternate therapies should be developed since highly active antiretroviral therapy is currently ineffective at treating HAND.

Glutamine Antagonist JHU083 Normalizes Aberrant Glutamate Production and Cognitive Deficits in the EcoHIV Murine Model of HIV-Associated Neurocognitive Disorders

HIV-associated neurocognitive disorders (HAND) have been linked to dysregulation of glutamate metabolism in the central nervous system (CNS) culminating in elevated extracellular glutamate and disrupted glutamatergic neurotransmission. Increased glutamate synthesis via upregulation of glutaminase (GLS) activity in brain immune cells has been identified as one potential source of excess glutamate in HAND. However, direct evidence for this hypothesis in an animal model is lacking, and the viability of GLS as a drug target has not been explored. In this brief report, we demonstrate that GLS inhibition with the glutamine analogue 6-diazo-5-oxo-L-norleucine (DON) can reverse cognitive impairment in the EcoHIV-infected mouse model of HAND. However, due to peripheral toxicity DON is not amenable to clinical use in a chronic disease such as HAND. We thus tested JHU083, a novel, brain penetrant DON prodrug predicted to exhibit improved tolerability. Systemic administration of JHU083 reversed cognitive impairment in EcoHIV-infected mice similarly to DON, and simultaneously normalized EcoHIV-induced increases in cerebrospinal fluid (CSF) glutamate and GLS activity in microglia-enriched brain CD11b + cells without observed toxicity. These studies support the mechanistic involvement of elevated microglial GLS activity in HAND pathogenesis, and identify JHU083 as a potential treatment option. Graphical Abstract Please provide Graphical Abstract caption.Glutamine Antagonist JHU083 Normalizes Aberrant Glutamate Production and Cognitive Deficits in the EcoHIV Murine Model of HIV-Associated Neurocognitive Disorders .

HIV/neuroAIDS biomarkers

HIV infection often causes neurological symptoms including cognitive and motor dysfunction, which have been collectively termed HIV/neuroAIDS. Neuropsychological assessment and clinical symptoms have been the primary diagnostic criteria for HIV/neuroAIDS, even for the mild cognitive and motor disorder, the most prevalent form of HIV/neuroAIDS in the era of combination antiretroviral therapy. Those performance-based assessments and symptoms are generally descriptive and do not have the sensitivity and specificity to monitor the diagnosis, progression, and treatment response of the disease when compared to objective and quantitative laboratory-based biological markers, or biomarkers. In addition, effects of demographics and comorbidities such as substance abuse, psychiatric disease, nutritional deficiencies, and co-infection on HIV/neuroAIDS could be more readily determined using biomarkers than using neuropsychological assessment and clinical symptoms. Thus, there have been great efforts in identification of HIV/neuroAIDS biomarkers over the past two decades. The need for reliable biomarkers of HIV/neuroAIDS is expected to increase as the HIV-infected population ages and their vulnerability to neurodegenerative diseases, particularly Alzheimer's disease increases. Currently, three classes of HIV/neuroAIDS biomarkers are being pursued to establish objective laboratory-based definitions of HIV-associated neurologic injury: cerebrospinal fluid biomarkers, blood biomarkers, and neuroimaging biomarkers. In this review, we will focus on the current knowledge in the field of HIV/neuroAIDS biomarker discovery.

Reliability of White Matter Microstructural Changes in HIV Infection: Meta-Analysis and Confirmation

BACKGROUND

Diffusion tensor imaging has been widely used to measure HIV effects on white matter microarchitecture. While many authors have reported reduced fractional anisotropy and increased mean diffusivity in HIV, quantitative inconsistencies across studies are numerous.

PURPOSE

Our aim was to evaluate the consistency across studies of HIV effects on DTI measures and then examine the DTI reliability in a longitudinal seropositive cohort.

DATA SOURCES

Published studies and investigators.

STUDY SELECTION

The meta-analysis included 16 cross-sectional studies reporting fractional anisotropy and 12 studies reporting mean diffusivity in the corpus callosum.

DATA ANALYSIS

Random-effects meta-analysis was used to estimate study standardized mean differences and heterogeneity. DTI longitudinal reliability was estimated in seropositive participants studied before and 3 and 6 months after beginning treatment.

DATA SYNTHESIS

Meta-analysis revealed lower fractional anisotropy (standardized mean difference, -0.43; P < .001) and higher mean diffusivity (standardized mean difference, 0.44; P < .003) in seropositive participants. Nevertheless, between-study heterogeneity accounted for 58% and 66% of the observed variance (P < .01). In contrast, the longitudinal cohort fractional anisotropy was higher and mean diffusivity was lower in seropositive participants (both, P < .001), and fractional anisotropy and mean diffusivity measures were very stable during 6 months, with intraclass correlation coefficients all >0.96.

LIMITATIONS

Many studies pooled participants with varying treatments, ages, and disease durations.

CONCLUSIONS

HIV effects on WM microstructure had substantial variations that could result from acquisition, processing, or cohort-selection differences. When acquisition parameters and processing were carefully controlled, the resulting DTI measures did not show high temporal variation. HIV effects on WM microstructure may be age-dependent. The high longitudinal reliability of DTI WM microstructure measures makes them promising disease-activity markers.

Association of Hippocampal Magnetic Resonance Imaging With Learning and Memory Deficits in HIV-1-Seropositive Patients

OBJECTIVE

To investigate the relationship between cognitive impairment and hippocampal morphological and functional changes in HIV-seropositive patients.

METHODS

Thirty HIV+ patients who complain of memory decrease and 15 healthy volunteers were recruited. Performances of learning and memory were assessed using Hopkins Verbal Learning Test-Revised (HVLT-R) and Brief Visuospatial Memory Test-Revised (BVMT-R). Bilateral hippocampal volume, apparent diffusion coefficient (ADC) value, fractional anisotropy value, and magnetic resonance spectroscopy variables of bilateral hippocampus and parahippocampal gyrus were detected by 3.0 T magnetic resonance scanner.

RESULTS

We found significant differences in all cognitive outcomes but one between HIV+ and HIV- patients. There was a difference in the ADC value of left parahippocampal gyrus between mild-impairment group and severe-impairment group (P = 0.018). We found differences in the choline (Cho), Cho/creatinine (Cr), and N-acetylaspartate/Cr of left hippocampus (P = 0.002, P = 0.008, P = 0.002) and the Cho/Cr of right parahippocampal gyrus (P = 0.023) between HIV+ and HIV- patients and in the myoinositol of left hippocampus (P = 0.003) and the glutamate and glutamine of right hippocampus (P < 0.001) between mild-impairment group and severe-impairment group. We found significant positive correlations between N-acetylaspartate/Cr of left hippocampus and outcomes of HVLT-R and BVMT-R. There were significant negative correlations between ADC values of hippocampus and parahippocampal gyrus and outcomes of HVLT-R and BVMT-R and between Cho and Cho/Cr of hippocampus and parahippocampal gyrus and outcomes of HVLT-R and BVMT-R.

CONCLUSIONS

The performance of verbal learning and visual memory was significantly decreased in HIV-1-seropositive patients. The cognitive impairment of HIV infection was associated with conductive function and metabolic changes of hippocampus and parahippocampal gyrus in this study.

White matter structure alterations in HIV-1-infected men with sustained suppression of viraemia on treatment

OBJECTIVE

Cognitive impairment is highly prevalent in HIV-1-infected (HIV+) patients, despite adequate suppression of viral replication by combination antiretroviral therapy (cART). Cerebral white matter structure alterations are often associated with cognitive impairment and have commonly been reported in the natural course of HIV infection. However, the existence of these alterations in adequately treated HIV+ patients remains unknown, as well as its possible association with cognitive impairment.

DESIGN

We used diffusion tensor imaging (DTI) to investigate whether white matter structure alterations exist in HIV+ patients with sustained suppressed viral replication on cART, and if such alterations are related to HIV-associated cognitive deficits.

METHODS

We compared 100 aviraemic HIV+ men on cART with 70 HIV-uninfected, otherwise comparable men. Clinical and neuropsychological assessments were performed. From DTI data, white matter fractional anisotropy and mean diffusion were calculated. Subsequently, tract-based spatial statistics (TBSS) was performed, with and without masking out white matter lesions.

RESULTS

HIV+ patients showed diffuse white matter structure alterations as compared with HIV-uninfected controls, observed as widespread decreased fractional anisotropy and an increased mean diffusion. These white matter structure alterations were associated with the number of years spent with a CD4 cell count below 500 cells/μl, but not with HIV-associated cognitive deficits.

CONCLUSION

Cerebral white matter structure alterations are found in middle-aged HIV+ men with sustained suppression of viraemia on cART, and may result from periods with immune deficiency when viral toxicity and host-inflammatory responses were at their peak. These white matter structure alterations were not associated with the observed subtle HIV-associated cognitive deficits.

VIDEO ABSTRACT

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White Matter Development is Potentially Influenced in Adolescents with Vertically Transmitted HIV Infections: A Tract-Based Spatial Statistics Study

BACKGROUND AND PURPOSE

Convergent evidence indicates that HIV is associated with abnormal WM microstructure in adults. However, little is known about whether HIV affects WM development in adolescents. In this study, we used DTI to investigate the integrity of WM microstructure in adolescents with vertically transmitted HIV infections.

MATERIALS AND METHODS

Fifteen HIV-positive adolescents with vertically transmitted infections and 26 HIV-negative controls participated in this study. Whole-brain analysis of fractional anisotropy was performed by Tract-Based Spatial Statistics to localize abnormal WM regions between groups. VOI analysis was further performed to explore the changes in diffusivity indices in the regions with fractional anisotropy alterations. Correlation analyses were used to assess the relationship between fractional anisotropy alterations and clinical measures within the HIV-positive group.

RESULTS

Relative to HIV-negative controls, HIV-positive adolescents demonstrated significantly reduced fractional anisotropy in the corpus callosum, superior and posterior corona radiata, frontal and parietal WM, pre-/postcentral gyrus, and superior longitudinal fasciculus. In the affected regions, fractional anisotropy reductions were caused by an increase in radial diffusivity, and no changes were observed in axial diffusivity. Moreover, fractional anisotropy values in the bilateral frontal WM were negatively correlated with the duration of highly active antiretroviral therapy and were positively associated with the age at onset of highly active antiretroviral therapy.

CONCLUSIONS

These findings suggest that early HIV infections may affect WM development, especially in the frontal WM, corpus callosum, and corona radiata in adolescents, which may be associated with hypomyelination and demyelination. Moreover, WM integrity may serve as a potential new treatment target.

A longitudinal magnetization transfer imaging evaluation of brain injury in a macaque model of neuroAIDS

Magnetization transfer (MT) imaging has been explored in prior studies of HIV patients and showed the potential capacity to assess brain injury after HIV infection. In the present study, adult pig-tailed macaques were infected with a highly neuropathogenic virus SIVsmmFGb. MT imaging was exploited to examine the monkey brains before simian immunodeficiency virus (SIV) inoculation and 2, 4, 8, 12, 16, and 20 weeks post-SIV inoculation. Blood samples were collected from each animal for monitoring CD4(+) and CD8(+) T cells before each MRI scan. The MT ratios (MTR) in several brain regions of interest were evaluated longitudinally. Significant reductions of MTR were observed in whole brain and selected regions of interest (genu, splenium, thalamus, caudate, centrum semiovale, frontal white matter, frontal gray matter, and putamen) in the SIV-infected monkeys, consistent with those reported previously in HIV patients. In particular, the longitudinal results indicate that abnormal MTR reduction can be detected as early as in 2 weeks and MTR may be more sensitive to the brain injury in cortical regions than in subcortical regions during acute SIV infection. In addition, MTR reduction in genu, centrum semiovale, and thalamus significantly correlated with the CD4(+) T cell percentage decrease. Also, the MTR reduction in thalamus correlated with the CD8(+) T cell percentage elevation. Taken together, this study reported the longitudinal evolution of MTR in different brain regions during SIV infection and further validates previous findings in HIV patients. The preliminary results suggest that MT imaging could be a robust and sensitive approach to characterize the neurodegeneration after SIV or HIV infection.

Role of neuroimaging in HIV-associated neurocognitive disorders

Human immunodeficiency virus (HIV) enters the brain soon after seroconversion and can cause HIV-associated neurocognitive disorders (HAND). Although the more severe and progressive forms of HAND are less prevalent due to combination antiretroviral therapy (cART), ∼ 40% of HIV-infected (HIV+) patients continue to have cognitive impairment. Some HIV+ individuals who have effective plasma HIV-1 RNA suppression with cART still develop HAND. It is often difficult to diagnose HAND in the outpatient setting as detailed neuropsychological performance testing is required. Additional biomarkers that are relatively easy to obtain and clinically relevant are needed for assessing HIV-associated neuropathologic changes. Recently developed noninvasive magnetic resonance imaging (MRI) techniques have great potential to serve as biomarkers. The authors review the application of some of these neuroimaging techniques, magnetic resonance spectroscopy (MRS), volumetric MRI, diffusion tensor imaging (DTI), functional MRI (fMRI), in HIV+ individuals. Each of the neuroimaging methods offers unique insight into mechanisms underlying neuroHIV, could monitor disease progression, and may assist in evaluating the efficacy of particular cART regimens. It is hoped that considerable progress will continue to occur such that some of these neuroimaging methods will be incorporated across multiple sites and included in future HAND guidelines.

Neuroimaging of rapidly progressive dementias, part 2: prion, inflammatory, neoplastic, and other etiologies

Most dementias begin insidiously, developing slowly and generally occurring in the elderly age group. The so-called rapidly progressive dementias constitute a different, diverse collection of conditions, many of which are reversible or treatable. For this reason, accurate identification and assessment of acute and subacute forms of dementia are critical to effective treatment; neuroimaging aids greatly in narrowing the diagnosis of these conditions. This second installment of a 2-part review of rapidly progressive dementias examines the use of imaging in an assortment of other etiologies in the differential diagnosis, from prion disease and neoplastic-related conditions to rare metabolic and other conditions such as Wernicke encephalopathy. In these clinical conditions, MR imaging has the potential to narrow this broad differential diagnosis and, at times, can definitively aid in the diagnosis of certain conditions on the basis of typical imaging patterns.

Translational spatial task and its relationship to HIV-associated neurocognitive disorders and apolipoprotein E in HIV-seropositive women

HIV-associated neurocognitive disorders (HAND) continue to be a neurological complication of HIV infection in the era of combined antiretroviral therapy. Hippocampal neurodegeneration and dysfunction occurs as a result of HIV infection, but few studies to date have assesses spatial learning and memory function in patients with HAND. We used the Memory Island (MI) test to study the effects of HIV infection, apolipoprotein E (ApoE) allele status, and cerebral spinal fluid (CSF) ApoE protein levels on spatial learning and memory in our cohort of Hispanic women. The MI test is a virtual reality-based computer program that tests spatial learning and memory and was designed to resemble the Morris Water Maze test of hippocampal function widely used in rodent studies. In the current study, HIV-seropositive women (n = 20) and controls (n = 16) were evaluated with neuropsychological (NP) tests, the MI test, ApoE, and CSF ApoE assays. On the MI, the HIV-seropositive group showed significant reduced learning and delayed memory performance compared with HIV-seronegative controls. When stratified by cognitive performance on NP tests, the HIV-seropositive, cognitively impaired group performed worse than HIV-seronegative controls in ability to learn and in the delayed memory trial. Interestingly, differences were observed in the results obtained by the NP tests and the MI test for ε4 carriers and noncarriers: NP tests showed effects of the ε4 allele in HIV-seronegative women but not HIV-seropositive ones, whereas the converse was true for the MI test. Our findings suggest that the MI test is sensitive in detecting spatial deficits in HIV-seropositive women and that these deficits may arise relatively early in the course of HAND.

The effects of HIV and combination antiretroviral therapy on white matter integrity

OBJECTIVE

HIV preferentially affects white matter in the brain. Although combination antiretroviral therapy (cART) reduces HIV viral load within the brain, continued inflammation can persist. We investigated the effect of HIV and cART on white matter integrity.

DESIGN

We used diffusion tensor imaging (DTI) to examine the effects of HIV and cART on white matter integrity within the corpus callosum and centrum semiovale (CSO).

METHODS

Neuropsychological testing and DTI measures (fractional anisotropy, mean diffusivity, axial diffusivity, radial diffusivity) were obtained from 21 HIV-uninfected controls, 21 HIV-infected patients naive to cART (HIV+/cART-), and 21 HIV+ patients receiving stable cART (HIV+/cART+). A subset of the HIV+/cART- individuals (n=10) was assessed before and 6 months after receiving medications. Differences among the cross-sectional groups were assessed using an analysis of variance, whereas paired t-tests evaluated longitudinal changes.

RESULTS

HIV+/cART- participants had significantly lower mean diffusivity, axial diffusivity, and radial diffusivity for the corpus callosum and CSO compared to HIV- controls and HIV+/cART+ individuals. No significant difference existed between HIV- controls and HIV+/cART+ patients. cART initiation significantly improved mean diffusivity, radial diffusivity, and axial diffusivity, but not fractional anisotropy, in the corpus callosum and CSO in some HIV-infected patients.

CONCLUSION

Observed decreases in DTI parameters between HIV+/cART+ and HIV+/cART- individuals could reflect the presence of inflammatory cells or cytotoxic edema in HIV+/cART- patients. Initiating cART could lead to a reduction in neuro-inflammation and improvement in DTI measures. Future DTI studies may be useful for evaluating the efficacy higher brain penetrating cART regimens.

A comparative evaluation of quantitative neuroimaging measurements of brain status in HIV infection

Diffusion tensor imaging (DTI), magnetization transfer imaging (MT) and automated brain volumetry were used to summarize brain involvement in human immunodeficiency virus (HIV) infection. A multiparametric neuroimaging protocol was implemented at 1.5 T in 10 HIV+ and 24 controls. Various summary parameters were calculated based on DTI, MT, and automated brain volumetry. The magnitude of the difference, as well as the between-group discrimination, was determined for each measure. Bivariate correlations were computed and redundancy among imaging parameters was examined by principal factor analysis. Significant or nearly significant differences were found for most measures. Large Cohen's d effect sizes were indicated for mean diffusivity (MD), fractional anisotropy (FA), magnetization transfer ratio (MTR) and gray matter volume fraction (GM). Between-group discrimination was excellent for FA and MTR and acceptable for MD. Correlations among all imaging parameters could be explained by three factors, possibly reflecting general atrophy, neuronal loss, and alterations. This investigation supports the utility of summary measurements of brain involvement in HIV infection. The findings also support assumptions concerning the enhanced sensitivity of DTI and MT to atrophic as well as alterations in the brain. These findings are broadly generalizable to brain imaging studies of physiological and pathological processes.

Soluble and cell-associated insulin receptor dysfunction correlates with severity of HAND in HIV-infected women

BACKGROUND

Blood sugar metabolism abnormalities have been identified in HIV-infected individuals and associated with HIV-associated neurocognitive disorders (HAND). These abnormalities may occur as a result of chronic HIV infection, long-term use of combined antiretroviral treatment (CART), aging, genetic predisposition, or a combination of these factors, and may increase morbidity and mortality in this population.

OBJECTIVE

To determine if changes in soluble and cell-associated insulin receptor (IR) levels, IR substrate-1 (IRS-1) levels, and IRS-1 tyrosine phosphorylation are associated with the presence and severity of HAND in a cohort of HIV-seropositive women.

METHODS AND RESULTS

This is a retrospective cross-sectional study using patient database information and stored samples from 34 HIV-seropositive women and 10 controls without history of diabetes from the Hispanic-Latino Longitudinal Cohort of Women. Soluble IR subunits [sIR, ectodomain (α) and full-length or intact (αβ)] were assayed in plasma and CSF samples by ELISA. Membrane IR levels, IRS-1 levels, and IRS-1 tyrosine phosphorylation were analyzed in CSF white cell pellets (WCP) using flow cytometry. HIV-seropositive women had significantly increased levels of intact or full-length sIR in plasma (p<0.001) and CSF (p<0.005) relative to controls. Stratified by HAND, increased levels of full-length sIR in plasma were associated with the presence (p<0.001) and severity (p<0.005) of HAND. A significant decrease in IRS-1 tyrosine-phosphorylation in the WCP was also associated with the presence (p<0.02) and severity (p<0.02) of HAND.

CONCLUSIONS

This study provides evidence that IR secretion is increased in HIV-seropositive women, and increased IR secretion is associated with cognitive impairment in these women. Thus, IR dysfunction may have a role in the progression of HAND and could represent a biomarker for the presence and severity of HAND.

Early microstructural white matter changes in patients with HIV: a diffusion tensor imaging study

BACKGROUND

Previous studies have reported white matter (WM) brain alterations in asymptomatic patients with human immunodeficiency virus (HIV).

METHODS

We compared diffusion tensor imaging (DTI) derived WM fractional anisotropy (FA) between HIV-patients with and without mild macroscopic brain lesions determined using standard magnetic resonance imaging (MRI). We furthermore investigated whether WM alterations co-occurred with neurocognitive deficits and depression. We performed structural MRI and DTI for 19 patients and 19 age-matched healthy controls. Regionally-specific WM integrity was investigated using voxel-based statistics of whole-brain FA maps and region-of-interest analysis. Each patient underwent laboratory and neuropsychological tests.

RESULTS

Structural MRI revealed no lesions in twelve (HIV-MRN) and unspecific mild macrostructural lesions in seven patients (HIV-MRL). Both analyses revealed widespread FA-alterations in all patients. Patients with HIV-MRL had FA-alterations primarily adjacent to the observed lesions and, whilst reduced in extent, patients with HIV-MRN also exhibited FA-alterations in similar regions. Patients with evidence of depression showed FA-increase in the ventral tegmental area, pallidum and nucleus accumbens in both hemispheres, and patients with evidence of HIV-associated neurocognitive disorder showed widespread FA-reduction.

CONCLUSION

These results show that patients with HIV-MRN have evidence of FA-alterations in similar regions that are lesioned in HIV-MRL patients, suggesting common neuropathological processes. Furthermore, they suggest a biological rather than a reactive origin of depression in HIV-patients.

Diffusion imaging in brain infections

Diffusion-weighted magnetic resonance imaging (DWI) provides image contrasts that are different from conventional magnetic resonance techniques. DWI is particularly sensitive for detecting acute ischemic stroke, but it also has many other clinical applications, including the evaluation of central nervous system (CNS) infections. This article addresses the role of DWI in the differential diagnosis of CNS infections, and discusses the most common DWI findings for each type of infection.

Marked relationship between matrix metalloproteinase 7 and brain atrophy in HIV infection

Circulating levels of matrix metalloproteinases (MMP-1 and 7) have been found to correlate with the severity of brain injury in HIV-infected subjects. This study used high-resolution neuroanatomic imaging and automated segmentation algorithms to clarify this relationship. Both metalloproteinases were significantly correlated with increased cerebrospinal fluid volume fraction. Comprehensive brain volumetric analysis revealed a more marked relationship with atrophy for MMP-7, which was significantly correlated with neural injury in multiple brain regions and nearly all ventricular measurements. MMP-7 was also correlated with measures of virologic and cognitive status.

The role of medical imaging in defining CNS abnormalities associated with HIV-infection and opportunistic infections

In this review of the current literature, we examine the role of medical imaging in providing new and relevant information on central nervous system (CNS) injury associated with human immunodeficiency virus (HIV) infection and various clinical manifestations of this injury. Common imaging modalities used to examine CNS injury in HIV infection include structural magnetic resonance imaging, magnetic resonance spectroscopy, diffusion tensor imaging, functional MRI, and positron emissions tomography. Clinical implications for the findings are discussed for each of these modalities individually and collectively. In addition, the direction for future studies is suggested in an attempt to provide possible methods that might answer the many questions that remain to be answered on the evolution and progression of CNS injury in the context of HIV infection.

Serum matrix metalloproteinase levels correlate with brain injury in human immunodeficiency virus infection

Circulating levels of specific matrix metalloproteinases (MMPs; 1 and 7) were evaluated as correlates of brain injury in eight individuals in advanced human immunodeficiency virus (HIV) infection. Neurological status was quantified in vivo with automated segmentation algorithms and with diffusion tensor imaging. Both metalloproteinases correlated with microstructural brain alterations and the degree of atrophy. MMPs may influence neurological outcome through involvement in neuroimmune response, blood-brain barrier permeability, leukocyte migration, and MMP-mediated neurotoxicity.

Quantitative diffusion tensor imaging tractography metrics are associated with cognitive performance among HIV-infected patients

There have been many studies examining HIV-infection-related alterations of magnetic resonance imaging (MRI) diffusion metrics. However, examining scalar diffusion metrics ignores the orientation aspect of diffusion imaging, which can be captured with tractography. We examined five different tractography metrics obtained from global tractography maps (global tractography FA, average tube length, normalized number of streamtubes, normalized weighted streamtube length, and normalized total number of tubes generated) for differences between HIV positive and negative patients and the association between the metrics and clinical variables of disease severity. We also examined the relationship between these metrics and cognitive performance across a wide range of cognitive domains for the HIV positive and negative patient groups separately. The results demonstrated a significant difference between the groups for global tractography FA (t = 2.13, p = 0.04), but not for any of the other tractography metrics examined (p-value range = 0.39 to 0.95). There were also several significant associations between the tractography metrics and cognitive performance (i.e., tapping rates, switching 1 and 2, verbal interference, mazes; r > or = 0.42) for HIV infected patients. In particular, associations were noted between tractography metrics, speed of processing, fine motor control/speed, and executive function for the HIV-infected patients. These findings suggest that tractography metrics capture clinically relevant information regarding cognitive performance among HIV infected patients and suggests the importance of subtle white matter changes in examining cognitive performance.

Biomarkers of neurological status in HIV infection: a 3-year study

PURPOSE

To evaluate circulating cytokines and chemokines as correlates of the degree of brain injury in individuals with advanced human immunodeficiency virus (HIV) infection.

EXPERIMENTAL DESIGN

Study participants included ten well-characterized subjects in advanced stage HIV infection. High-throughput multiplexed analysis was used to quantify markers of interest at baseline and 3 years later in the clinical course. Objective measurements of the brain were derived in vivo with quantitative magnetic resonance segmentation algorithms and with diffusion tensor imaging.

RESULTS

Of the markers examined, monocyte chemoattractant protein-1 (MCP-1 or CCL-2) was the most prominent correlate of brain injury. Elevated MCP-1 levels correlated with brain white matter alterations at the initial assessment. The relationship to injury was more extensive 3 years later; elevated MCP-1 was significantly correlated with measures of brain microstructural alterations and of abject atrophy.

CONCLUSIONS AND CLINICAL RELEVANCE

The findings build on our prior observations that elevated MCP-1 levels may be a useful predictive marker for HIV-associated neurocognitive disorder. As a potent chemoattractant, MCP-1 may mediate injury through participation in self-reinforcing cycles of chronic immune activation and cytokine/chemokine-mediated neurotoxicity.

White matter abnormalities revealed by diffusion tensor imaging in non-demented and demented HIV+ patients

HIV associated dementia (HAD) is the most advanced stage of central nervous system disease caused by HIV infection. Previous studies have demonstrated that patients with HAD exhibit greater cerebral and basal ganglia atrophy than non-demented HIV+ (HND) patients. However, the extent to which white matter is affected in HAD patients compared to HND patients remains elusive. This study is designed to address the potential white matter abnormalities through the utilization of diffusion tensor imaging (DTI) in both HND and HAD patients. DTI and T1-weighted images were acquired from 18 healthy controls, 21 HND and 8 HAD patients. T1 image-based registration was performed to 1) parcellate the whole brain white matter into major white matter regions, including frontal, parietal, temporal and occipital white matter, corpus callosum and internal capsule for statistical comparisons of the mean DTI values, and 2) warp all DTI parametric images towards the common template space for voxel-based analysis. The statistical comparisons were performed with four DTI parameters including fractional anisotropy (FA), mean (MD), axial (AD), and radial (RD) diffusivities. With Whitney U tests on the mean DTI values, both HND and HAD demonstrated significant differences from the healthy control in multiple white matter regions. In addition, HAD patients exhibited significantly elevated MD and RD in the parietal white matter when compared to HND patients. In the voxel-based analysis, widespread abnormal regions were identified for both HND and HAD patients, although a much larger abnormal volume was observed in HAD patients for all four DTI parameters. Furthermore, both region of interest (ROI) based and voxel-based analyses revealed that RD was affected to a much greater extent than AD by HIV infection, which may suggest that demyelination is the prominent disease progression in white matter.

Cortical atrophy and white matter hyperintensities in HIV: the Hawaii Aging with HIV Cohort Study

BACKGROUND

As many human immunodeficiency virus (HIV)-seropositive individuals are now living longer after infection because of highly active antiretroviral therapy, aging-related manifestations of cerebral small-vessel ischemic vascular disease, such as brain white matter hyperintensities (WMHs), are becoming increasingly important in this population.

GOALS

This study was designed to determine the relationship between WMHs and cortical volumes in HIV-seropositive individuals.

MATERIALS AND METHODS

Voxel-based morphometry was used to compare cortical volumes among 62 HIV-seropositive individuals participating in the Hawaii Aging with HIV Cohort Study, 30 with moderate WMHs and 32 with minimal or no WMHs.

RESULTS

Presence of moderate WMHs was associated with decreased cortical volumes in the frontal lobes bilaterally.

CONCLUSION

These findings suggest that age-related WMHs are associated with reduced frontal gray matter volumes in HIV-seropositive individuals, supporting the hypothesis that the frontal lobes may have greater susceptibility to the effects of small-vessel ischemic vascular disease.

HIV-associated alterations in normal-appearing white matter: a voxel-wise diffusion tensor imaging study

OBJECTIVE

There are conflicting reports of adverse HIV-associated alterations in white matter integrity as measured by diffusion tensor imaging (DTI). We sought to address these conflicting reports by assessing, on a voxel-by-voxel basis, HIV-associated regional changes in radiologically defined normal-appearing white matter (NAWM) integrity using high-resolution DTI.

METHODS

30 HIV-seropositive (SP) and 30 HIV-seronegative (SN) nondemented, community-dwelling participants underwent DTI to derive whole-brain measures of white matter integrity (fractional anisotropy [FA] and mean diffusivity [MD]). For each participant, the white matter T2 volume was thresholded to remove regions of abnormal signal, resulting in a NAWM mask, which was then applied to the FA and MD volumes to extract voxel-wise NAWM measures of white matter integrity. Voxel-wise group comparisons of FA and MD were conducted (P < 0.005, extent threshold 5 voxels) while controlling for age and substance-abuse history.

RESULTS

There were no significant differences between the groups for demographic or cognitive performance variables. Summary whole-brain measures of FA and MD were equivalent between the SP and SN samples. Among the SP sample, history of substance abuse was associated with significantly increased whole-brain NAWM MD, and coinfection with hepatitis C virus (HCV) was associated with a trend for increased MD. Correlations between whole-brain NAWM FA and MD with cognitive performance measures were not significant. Regional analyses of DTI measures revealed variable differences in NAWM FA in the SP sample, with findings of both decreased and increased FA. Differences in NAWM MD were more consistent, with widespread increases noted in the SP sample compared to the SN sample. Eight of the 10 regions displaying significantly increased FA in the SP sample were also found to have significantly increased MD compared to the SN sample.

CONCLUSIONS

Decreased white matter integrity is present even in radiologically defined NAWM in nondemented, community-dwelling patients with HIV. The decrease in NAWM integrity is best seen in increases in MD, a measure of generalized tissue breakdown. Indications of NAWM axonal integrity (FA) present a more complicated picture, with both decreased FA and increased FA in the SP sample. Our findings of variable HIV-associated FA changes in NAWM may account for previous conflicting reports of changes in DTI parameters in this population. The results of our study suggest that HIV infection contributes to variable changes in DTI values, reflecting both direct loss of axonal integrity and a loss of complexity to the underlying axonal matrix.

Whole brain and localized magnetization transfer measurements are associated with cognitive impairment in patients infected with human immunodeficiency virus

BACKGROUND AND PURPOSE

Patients infected with human immunodeficiency virus (HIV) are susceptible to cognitive deterioration. This study investigated the utility of magnetization transfer (MT) imaging for quantification of brain tissue alterations associated with cognitive deficits in patients with HIV.

MATERIALS AND METHODS

MT ratios (MTR) were derived for whole brain and for regions of interest (ROIs) in the basal ganglia and white matter in 11 HIV and 12 control subjects. Relationships with severity of cognitive impairment and specific neuropsychological deficits were also evaluated.

RESULTS

MTR values for normalized whole brain histogram peak height, whole brain histogram mean, and all examined ROIs were reduced in the HIV subjects. Normalized histogram peak height and mean for whole brain, as well as means for the corpus callosum, basal ganglia, and frontal white matter (FWM), were significantly correlated with severity of cognitive impairment. MTR values for white matter regions (corpus callosum, FWM, and centrum semiovale) were correlated with specific cognitive deficits.

CONCLUSION

Quantitative MTR measurements, determined for the whole brain and for vulnerable ROIs, are sensitive to neuropathologic changes associated with cognitive impairment in HIV-infected patients.

Magnetization transfer magnetic resonance imaging of the brain, spinal cord, and optic nerve

Magnetic resonance imaging is highly sensitive in revealing CNS abnormalities associated with several neurological conditions, but lacks specificity for their pathological substrates. In addition, MRI does not allow evaluation of the presence and extent of damage in regions that appear normal on conventional MRI sequences and that postmortem studies have shown to be affected by pathology. Quantitative MR-based techniques with increased pathological specificity to the heterogeneous substrates of CNS pathology have the potential to overcome such limitations. Among these techniques, one of the most extensively used for the assessment of CNS disorders is magnetization transfer MRI (MT-MRI). The application of this technique for the assessment of damage in macroscopic lesions, in normal-appearing white and gray matter, and in the spinal cord and optic nerve of patients with several neurological conditions is providing important in vivo information-dramatically improving our understanding of the factors associated with the appearance of clinical symptoms and the accumulation of irreversible disability. MT-MRI also has the potential to contribute to the diagnostic evaluation of several neurological conditions and to improve our ability to monitor treatment efficacy in experimental trials.

Small-Vessel Vascular Disease in Human Immunodeficiency Virus Infection: The Hawaii Aging with HIV Cohort Study

BACKGROUND

This study is designed to determine the relationship between age and occurrence of cerebral manifestations of small-vessel ischemic vascular disease in human immunodeficiency virus (HIV)-seropositive individuals.

METHODS

Periventricular leukoaraiosis severity and white matter lesion volume were determined by magnetic resonance imaging of the brain of 57 HIV-seropositive individuals.

RESULTS

Cerebral small-vessel ischemic vascular disease manifestations correlated with age and systolic blood pressure, but not with HIV infection-related parameters.

CONCLUSIONS

These findings suggest that, in the era of highly active antiretroviral therapy, leukoaraiosis severity and white matter lesion volume may be more indicative of small-vessel ischemic vascular disease than HIV-related CNS pathology, and support the need for aggressive treatment of vascular risk factors in HIV-seropositive individuals.

Monocyte chemoattractant protein-1 correlates with subcortical brain injury in HIV infection

Various biomarkers have been suggested as associative or predictive of HIV-associated neurocognitive impairment. Plasma levels of monocyte chemoattractant protein 1 (MCP-1), tumor necrosis factor alpha (TNF-alpha), and hematocrit were evaluated for relationships with diffusion tensor imaging measurements of centrum semiovale, caudate, and putamen. MCP-1 levels correlated with tissue status (mean diffusivity) in all examined regions. Plasma markers were also significantly correlated with anisotropy measurements in centrum semiovale (TNF-alpha) and putamen (hematocrit).

Magnetization transfer imaging in multiple sclerosis

Magnetization transfer (MT) is a relatively new way of generating contrast in magnetic resonance (MR) images that is sensitive to the density of the macromolecules found throughout tissue structures such as membranes, myelin, and organelles. MT imaging (MTI) can provide a quantitative measure of macromolecular density, and therefore of tissue damage, and has been applied in the central nervous system in multiple sclerosis (MS) and other diseases. This article introduces the contrast mechanisms behind MTI and gives some practical guidance about implementing MTI and about quantitative analysis of the MT scans. An overview of MT measurements made in animal studies, in postmortem tissue samples, and in other demyelinating diseases attempts to rationalize the pathological basis of changes in MT contrast in MS. The application of MTI to MS is reviewed, with emphasis on the contribution that MTI has made to the current understanding of the MS disease process, both its natural history and the response to treatment. The pathological basis of abnormal MT contrast is still open to debate, with many conflicting reports; indeed, it is unlikely that a simple measure of MT effect will reveal the details of pathology that is a combination of inflammation, demyelination, remyelination, and axonal loss. There is no doubt, however, that MT measurements have contributed to the current understanding of both disease progression and the response to treatment and will prove to be a valuable tool in the future, particularly if more refined techniques can be applied practically in multicenter studies.

Diffusion alterations in corpus callosum of patients with HIV

BACKGROUND AND PURPOSE

Diffusion alterations have been identified in the corpus callosum and frontal white matter of patients infected with human immunodeficiency virus (HIV), though the relevance of these findings to cognitive deterioration has not yet been determined. This study tested the hypothesis that diffusion tensor imaging can detect tissue status alterations in these regions in cognitively impaired patients infected with HIV and the acquired measurements correlate with the severity of cognitive impairment.

METHODS

Fractional anisotropy (FA) and mean diffusivity (MD) were determined for corpus callosum (genu and splenium) and frontal white matter (FWM). The DTI measurements were compared in 11 HIV and 11 control participants. Patterns of relationship were examined with cognitive status measures from concurrent neurologic and neuropsychologic evaluations.

RESULTS

FA values for the splenium were significantly reduced in the patients infected with HIV and correlated with dementia severity and deficits in motor speed. MD values for the splenium were significantly increased in the patients infected with HIV and correlated with deficits in motor speed. FA measurements were also significantly correlated with performance on visual memory (genu), visuoconstruction (FWM), and verbal memory (FWM) tasks.

CONCLUSION

Diffusion abnormalities were identified in the splenium of the corpus callosum in patients infected with HIV, and these alterations were associated with dementia severity and motor speed losses. In vivo assessment of callosal integrity by using quantitative neuroimaging may have potential utility as a marker of brain injury in patients infected with HIV.

Diffusion tensor imaging of subcortical brain injury in patients infected with human immunodeficiency virus

Diffusion tensor imaging (DTI) was used to derive in vivo tissue status measurements of subcortical brain regions that are vulnerable to injury in human immunodeficiency virus (HIV)-infected patients. Quantitative measurements, including the mean diffusivity (MD) and fractional anisotropy (FA), were determined in lateralized basal ganglia (caudate and putamen) and centrum semiovale in 11 well-characterized HIV patients and in 11 control subjects. DTI measurements were examined for patterns of relationship with markers of clinical and cognitive progression. DTI measures acquired in subcortical regions were significantly correlated with loss of function in specific cognitive domains. Significant relationships were identified between measures for putamen and verbal memory (MD), visual memory (FA), working memory (FA), and overall cognitive impairment (MD). Measures for caudate (FA) were significantly correlated with visual memory. Measures for centrum semiovale were significantly correlated with visual memory deficits (MD) and visuoconstruction (FA). Relationships between anisotropy measures and anemia (basal ganglia) and CD4 counts (centrum semiovale) were also observed. Findings from this investigation indicate that DTI is a sensitive tool for correlating neuroanatomic pathologic features with specific cognitive deficits in patients with HIV infection.