Neuropsychological impairment in prodromal Parkinson's disease

Dopamine across timescales and cell types: Relevance for phenotypes in Parkinson's disease progression

Dopamine neurons in the substantia nigra pars compacta (SNc) synthesize and release dopamine, a critical neurotransmitter for movement and learning. SNc dopamine neurons degenerate in Parkinson's Disease (PD), causing a host of motor and non-motor symptoms. Here, we review recent conceptual advances in our basic understanding of the dopamine system - including our rapidly advancing knowledge of dopamine neuron heterogeneity - with special attention to their importance for understanding PD. In PD patients, dopamine neuron degeneration progresses from lateral SNc to medial SNc, suggesting clinically relevant heterogeneity in dopamine neurons. With technical advances in dopamine system interrogation, we can understand the relevance of this heterogeneity for PD progression and harness it to develop new treatments.

Cognition and Other Non-Motor Symptoms in an At-Risk Cohort for Parkinson's Disease Defined by REM-Sleep Behavior Disorder and Hyposmia

Background

REM-sleep behavior disorder (RBD) and other non-motor symptoms such as hyposmia were proposed by the Movement Disorder Society as research criteria for prodromal Parkinson's disease (P-PD). Global cognitive deficit was later added.

Objective

To compare non-motor symptoms, focusing on cognition, between a P-PD group and a matched control group.

Methods

In this cross-sectional, case-control study, in a first set of analyses, we performed extensive cognitive testing on people with (n = 76) and a control group without (n = 195) probable RBD and hyposmia. Furthermore, we assessed motor and non-motor symptoms related to Parkinson's Disease (PD). After propensity score matching, we compared 62 P-PD with 62 age- and sex-matched controls. In addition, we performed regression analyses on the total sample (n = 271). In a second set of analyses, we used, a.o., the CUPRO to evaluate retrograde procedural memory and visuo-constructive functions.

Results

People with P-PD showed significantly poorer performances in global cognition, visuo-constructive and executive functions, mainly in mental flexibility (p < 0.001; p = 0.004; p = 0.003), despite similar educational levels (p = 0.415). We observed significantly more motor and non-motor symptoms (p < 0.001; p = 0.004), higher scores for depression (p = 0.004) and apathy (p < 0.001) as well as lower quality of life (p < 0.001) in P-PD.

CONCLUSIONS

Our findings confirm that global cognitive, executive, and visuo-constructive deficits define the P-PD group. In addition, depression, apathy, and lower quality of life were more prevalent in P-PD. If replicated in other samples, executive and visuo-constructive deficits should be considered in non-motor P-PD. Determining specific patterns will support early recognition of PD, secondary prevention of complications and the development of neuroprotective treatments.

Cognition in prodromal Parkinson's disease

One characteristic of Parkinson's disease (PD) is a prodromal phase, lasting many years during which both pre-clinical motor and non-motor symptoms occur. Around one-fifth of patients with PD manifest mild cognitive impairment at time of clinical diagnosis. Thus, important challenges are to define the time of onset of cognitive dysfunction in the prodromal phase of PD, and to define its co-occurrence with other specific characteristics. Evidence for cognitive change in prodromal PD comes from various study designs, including both longitudinal and cross-sectional approaches with different target groups. These studies support the concept that changes in global cognitive function and alterations in executive functions occur, and that these changes may be present up to 6 years before clinical PD diagnosis. Notably, this evidence led to including global cognitive impairment as an independent prodromal marker in the recently updated research criteria of the Movement Disorder Society for prodromal PD. Knowledge in this field, however, is still at its beginning, and evidence is sparse about many aspects of this topic. Further longitudinal studies including standardized assessments of global and domain-specific cognitive functions are needed to gain further knowledge about the first appearance, the course, and the interaction of cognitive deficits with other non-motor symptoms in prodromal stage PD. Treatment approaches, including non-pharmacological interventions, in individuals with prodromal PD might help to prevent or delay cognitive dysfunction in early PD.

Prodromal Cognitive Deficits and the Risk of Subsequent Parkinson’s Disease

Background: There is growing interest in identifying individuals who are in the prodromal phase of Parkinson’s disease (PD), as these individuals are potentially suitable for inclusion in intervention trials to prevent clinically manifest PD. However, it is less clear whether—and to what extent—cognitive deficits are present in prodromal PD. Methods: A systematic query was conducted through PubMed and Embase for prospective observational cohort studies that (a) assessed cognitive performance in individuals free of manifest PD at baseline and (b) subsequently followed up participants for incident PD. We grouped the results by cognitive domain, and for domains that had been reported in at least three separate studies, we performed random-effects, inverse variance meta-analyses based on summary statistics. Results: We identified nine articles suitable for inclusion, with a total of 215 patients with phenoconversion and 13,524 individuals remaining disease-free at follow-up. The studies were highly heterogeneous in study design, study population, and cognitive test batteries. Studies that included only cognitive screening measures such as MMSE or MoCA reported no association between worse cognitive performance and onset of manifest PD (combined odds ratio 1.08; 95% confidence interval 0.66–1.77). By contrast, studies that used extensive cognitive testing batteries found that global cognitive deficits were associated with an increased risk of manifest PD. In domain-specific analyses, there was evidence for an association between worse executive functioning (OR 1.45; 95% CI 1.10–1.92), but not memory (OR 1.20; 95% CI 0.85–1.70) or attention (OR 0.98; 95% CI 0.23–4.26), and clinically manifest PD. Conclusion: Although some caution due to high heterogeneity among published studies is warranted, the available evidence suggests that global and executive cognitive deficits are prodromal features of PD. Collaborative prospective studies with extensive cognitive test batteries are required to shed light on domain-specific deficits, temporal relations, and subgroup differences in prodromal cognitive deficits in PD.

Characterizing mild cognitive impairment in prodromal Parkinson's disease: A community-based study in China

Objective

The International Parkinson and Movement Disorder Society (MDS) has published research criteria for prodromal Parkinson's disease (pPD), which includes cognitive impairment as a prodromal marker. However, the clinical features of mild cognitive impairment (MCI) in pPD remain unknown. Our study aimed to evaluate the frequency and clinical features of mild cognitive impairment of pPD in the elderly in China.

Methods

The cross‐sectional community‐based study recruited 2688 participants aged ≥50 years. Subjects were diagnosed with pPD according to the MDS criteria. Overall, 39 pPD and 22 healthy controls underwent comprehensive clinical and neuropsychological assessment. MCI was also diagnosed by the MDS criteria. Next, we investigated the relationship between clinical factors and cognition.

Results

Among the 2,663 dementia‐free and Parkinson disease (PD)‐free participants, 55 met the criteria for pPD (2.1%) and 23 pPD met the criteria for MCI. Memory, attention/working memory, and executive function were the most frequent impaired domains, and amnestic MCI multidomain phenotype was the most frequent MCI subtype (69.57%) in pPD. Additionally, correlation analysis revealed that the global cognitive performance was negatively related to UPDRS‐III score (r = −0.456, p = 0.004).

Conclusion

MCI, specifically impairment in memory, attention/working memory, and executive domain, is present at the prodromal stage of PD. In addition, cognitive performance is correlated with motor symptoms in pPD. Our results reflect that cognitive profile, combined with motor symptoms, can help clinicians to identify individuals with pPD early, as those would be the optimal candidates for neuroprotective therapy.

Heterogeneity of prodromal Parkinson symptoms in siblings of Parkinson disease patients

A prodromal phase of Parkinson's disease (PD) may precede motor manifestations by decades. PD patients' siblings are at higher risk for PD, but the prevalence and distribution of prodromal symptoms are unknown. The study objectives were (1) to assess motor and non-motor features estimating prodromal PD probability in PD siblings recruited within the European PROPAG-AGEING project; (2) to compare motor and non-motor symptoms to the well-established DeNoPa cohort. 340 PD siblings from three sites (Bologna, Seville, Kassel/Goettingen) underwent clinical and neurological evaluations of PD markers. The German part of the cohort was compared with German de novo PD patients (dnPDs) and healthy controls (CTRs) from DeNoPa. Fifteen (4.4%) siblings presented with subtle signs of motor impairment, with MDS-UPDRS-III scores not clinically different from CTRs. Symptoms of orthostatic hypotension were present in 47 siblings (13.8%), no different to CTRs (p = 0.072). No differences were found for olfaction and overall cognition; German-siblings performed worse than CTRs in visuospatial-executive and language tasks. 3/147 siblings had video-polysomnography-confirmed REM sleep behavior disorder (RBD), none was positive on the RBD Screening Questionnaire. 173/300 siblings had <1% probability of having prodromal PD; 100 between 1 and 10%, 26 siblings between 10 and 80%, one fulfilled the criteria for prodromal PD. According to the current analysis, we cannot confirm the increased risk of PD siblings for prodromal PD. Siblings showed a heterogeneous distribution of prodromal PD markers and probability. Additional parameters, including strong disease markers, should be investigated to verify if these results depend on validity and sensitivity of prodromal PD criteria, or if siblings' risk is not elevated.

Cognitive function in men with non-motor features of Parkinson's disease

Objective

Subtle cognitive deficits can occur during the prodromal phase of Parkinson’s disease (PD), commonly in conjunction with hyposmia. However, little is known about the association between cognitive function and other features suggestive of prodromal PD. We evaluated the association of non-motor prodromal PD features, including hyposmia, constipation and probable REM sleep behaviour disorder (pRBD), with objective measures of cognitive function and self-reported cognitive decline.

Methods

The study population comprised 804 men who responded to a telephone cognitive interview in 2016–2017. Participants included 680 individuals with hyposmia, of whom 45 had confirmed PD, and 124 men without hyposmia. Among these men, we evaluated objective cognitive function and subjective cognitive decline to determine whether the presence of non-motor features of prodromal PD was associated with cognitive functioning. Analyses were adjusted for age, physical activity, body mass index, smoking status and coffee consumption.

Results

Individuals with non-motor features of prodromal PD had worse objective and subjective cognitive performance relative to men without non-motor features. Cognitive impairment was particularly prevalent among individuals with concurrent hyposmia, pRBD and constipation (multivariate-adjusted OR=3.80; 95% CI 1.52 to 9.47 for objective poor cognitive function; OR=8.71; 95% CI 3.18 to 23.83 for subjective cognitive decline). As expected, both objective (OR=7.91) and subjective (OR=17.42) cognitive impairment were also more common among men with confirmed PD.

Conclusions

Our study suggests that cognition is commonly affected in individuals with non-motor prodromal PD features, particularly when multiple of these features are present.

Is Attention-Deficit/Hyperactivity Disorder a Risk Syndrome for Parkinson's Disease?

Recent epidemiological evidence indicates that diagnosis of attention-deficit/hyperactivity disorder (ADHD) is associated with increased risk for diseases of the basal ganglia and cerebellum, including Parkinson's disease (PD). The evidence reviewed here indicates that deficits in striatal dopamine are a shared component of the causal chains that produce these disorders. Neuropsychological studies of adult ADHD, prodromal PD, and early-stage PD reveal similar deficits in executive functions, memory, attention, and inhibition that are mediated by similar neural substrates. These and other findings are consistent with the possibility that ADHD may be part of the PD prodrome. The mechanisms that may mediate the association between PD and ADHD include neurotoxic effects of stimulants, other environmental exposures, and Lewy pathology. Understanding the nature of the association between PD and ADHD may provide insight into the etiology and pathogenesis of both disorders. The possible contribution of stimulants to this association may have important clinical and public health implications.

Higher probability of prodromal Parkinson disease is related to lower cognitive performance

OBJECTIVE

Given the limited information on cognitive function before Parkinson disease (PD) clinical onset in the general population, we sought to assess prodromal PD (pPD) probability and relate it to detailed cognitive performance in a community cohort.

METHODS

In a population-based cohort of 1,629 dementia-free and PD-free participants ≥65 years of age in Greece, we assessed probability of pPD according to the International Parkinson and Movement Disorder Society's criteria. Clinical cognitive diagnoses (cognitively unimpaired, mild cognitive impairment [MCI], dementia) considering neuropsychological testing and functional status were assigned in consensus conferences. Cognitive performance in 5 cognitive domains was assessed by a detailed neuropsychological battery and summarized in the form of z scores. We investigated associations between pPD probability (and its individual constituents) and cognitive outcomes.

RESULTS

The median probability of pPD was 1.81% (0.2%-96.7%). Participants with MCI had higher probability of pPD compared to those with normal cognition (p < 0.001). Higher probability of pPD was related to lower performance in all cognitive domains (memory, language, executive, attention, and visuospatial function) (p < 0.001). Lower cognitive performance was further associated with certain nonmotor markers of pPD, such as daytime somnolence, depression, urinary dysfunction, constipation, and subthreshold parkinsonism (p < 0.001).

CONCLUSIONS

Higher probability of pPD was associated with lower cognitive performance in all domains and higher probability of MCI. This may reflect a widespread pathologic process although future studies are warranted to infer causality. These results suggest to clinicians that they should assess cognition early, and to researchers that they should further look into the possible mechanisms that may underlie this observation.

Cognitive changes in prodromal Parkinson's disease: A review

Although other nonmotor phenomena representing possible prodromal symptoms of Parkinson's disease have been described in some detail, the occurrence and characteristics of cognitive decline in this early phase of the disease are less well understood. The aim of this review is to summarize the current state of research on cognitive changes in prodromal PD. Only a small number of longitudinal studies have been conducted that examined cognitive function in individuals with a subsequent PD diagnosis. However, when we consider data from at-risk groups, the evidence suggests that cognitive decline may occur in a substantial number of individuals who have the potential for developing PD. In terms of specific cognitive domains, executive function in particular and, less frequently, memory scores are reduced. Prospective longitudinal studies are thus needed to clarify whether cognitive, and specifically executive, decline might be added to the prodromal nonmotor symptom complex that may precede motor manifestations of PD by years and may help to update the risk scores used for early identification of PD. © 2017 International Parkinson and Movement Disorder Society.