Cognitive profiles in Parkinson's disease and their relation to dementia: a data-driven approach

Systematic review of data-driven cognitive subtypes in Parkinson disease

BACKGROUND AND PURPOSE

Recent application of the mild cognitive impairment concept to Parkinson disease (PD) has proven valuable in identifying patients at risk of dementia. However, it has sparked controversy regarding the existence of cognitive subtypes. The present review evaluates the current literature pertaining to data-driven subtypes of cognition in PD.

METHODS

Following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, systematic literature searches for peer-reviewed articles on the topic of cognitive subtyping in PD were performed.

RESULTS

Twenty-two relevant articles were identified in the systematic search. Subtype structures showed either a spectrum of severity or specific domains of impairment. Domain-specific subtypes included amnestic/nonamnestic, memory/executive, and frontal/posterior dichotomies, as well as more complex structures with less definitive groupings. Preliminary longitudinal evidence showed some differences in cognitive progression among subtypes. Neuroimaging evidence provided insight into distinct patterns of brain alterations among subtypes.

CONCLUSIONS

Recurring phenotypes in the literature suggest strong clinical relevance of certain cognitive subtypes in PD. Although the current literature is limited, it raises critical questions about the utility of data-driven methods in cognitive research. The results encourage further integration of neuroimaging research to define the latent neural mechanisms behind divergent subtypes. Although there is no consensus, there appears to be growing consistency and inherent value in identifying cognitive subtypes in PD.

Mapping Actuarial Criteria for Parkinson’s Disease-Mild Cognitive Impairment onto Data-Driven Cognitive Phenotypes

Prevalence rates for mild cognitive impairment in Parkinson’s disease (PD-MCI) remain variable, obscuring the diagnosis’ predictive utility of greater dementia risk. A primary factor of this variability is inconsistent operationalization of normative cutoffs for cognitive impairment. We aimed to determine which cutoff was optimal for classifying individuals as PD-MCI by comparing classifications against data-driven PD cognitive phenotypes. Participants with idiopathic PD (n = 494; mean age 64.7 ± 9) completed comprehensive neuropsychological testing. Cluster analyses (K-means, Hierarchical) identified cognitive phenotypes using domain-specific composites. PD-MCI criteria were assessed using separate cutoffs (−1, −1.5, −2 SD) on ≥2 tests in a domain. Cutoffs were compared using PD-MCI prevalence rates, MCI subtype frequencies (single/multi-domain, executive function (EF)/non-EF impairment), and validity against the cluster-derived cognitive phenotypes (using chi-square tests/binary logistic regressions). Cluster analyses resulted in similar three-cluster solutions: Cognitively Average (n = 154), Low EF (n = 227), and Prominent EF/Memory Impairment (n = 113). The −1.5 SD cutoff produced the best model of cluster membership (PD-MCI classification accuracy = 87.9%) and resulted in the best alignment between PD-MCI classification and the empirical cognitive profile containing impairments associated with greater dementia risk. Similar to previous Alzheimer’s work, these findings highlight the utility of comparing empirical and actuarial approaches to establish concurrent validity of cognitive impairment in PD.

Time-course of decline in different cognitive domains in Parkinson's disease: a retrospective study

Cognitive impairment and dementia are common non-motor symptoms in Parkinson's disease (PD). To elucidate the potentially typical progression of cognitive decline in PD and its variation, we retrospectively surveyed neuropsychological data obtained at the Parkinson-Klinik Ortenau, Germany in the years 1996-2015. Many of the patients in the surveyed period were repeatedly admitted to our clinic and we were thus able to compile neuropsychological re-test data for 252 patients obtained at varying time intervals. Neuropsychological testing was conducted with the NAI (Nürnberger Alters-Inventar). This battery provides sub-tests that examine cognitive processing speed, executive function, working memory, and verbal/visual memory functions. The re-test time span varied across patients from below 1 year up to about 12 years. Most patients were seen twice, but some patients were tested up to eight times. The steepest rates of cognitive decline were observed for the NAI sub-tests Trail-Making, Maze Test, and Stroop-Word Reading/Color Naming. Intermediate rates of decline were found for Digit Span, Word List-Immediate Recall, and Picture Test. Stroop Test-Interference, Word List-Delayed Recognition, and Figure Test exhibited the slowest decline rates. We did not observe a significant effect of age at diagnosis or gender on the rate of decline. In sum, this study retrospectively evaluated cognitive decline in a sample of patients with PD. Our data suggest a broad cognitive decline that particularly affects the cognitive capacities for processing speed, executive functions, and immediate memory functions.

Reduced Gray Matter Volume and Risk of Falls in Parkinson's Disease with Dementia Patients: A Voxel-Based Morphometry Study

Purpose: Risk of falls is a common sequela affecting patients with Parkinson’s disease (PD). Although motor impairment and dementia are correlated with falls, associations of brain structure and cognition deficits with falls remain unclear. Material and Methods: Thirty-five PD patients with dementia (PDD), and 37 age- and sex-matched healthy subjects were recruited for this study. All participants received structural magnetic resonance imaging (MRI) scans, and disease severity and cognitive evaluations. Additionally, patient fall history was recorded. Regional structural differences between PDD with and without fall groups were performed using voxel-based morphometry processing. Stepwise logistic regression analysis was used to predict the fall risk in PDD patients. Results: The results revealed that 48% of PDD patients experienced falls. Significantly lower gray matter volume (GMV) in the left calcarine and right inferior frontal gyrus in PDD patients with fall compared to PDD patients without fall were noted. The PDD patients with fall exhibited worse UPDRS-II scores compared to PDD patients without fall and were negatively correlated with lower GMV in the left calcarine (p/r = 0.004/−0.492). Furthermore, lower GMV in the left calcarine and right inferior frontal gyrus correlated with poor attention and executive functional test scores. Multiple logistic regression analysis showed that the left calcarine was the only variable (p = 0.004, 95% CI = 0.00–0.00) negatively associated with the fall event. Conclusions: PDD patients exhibiting impaired motor function, lower GMV in the left calcarine and right inferior frontal gyrus, and notable cognitive deficits may have increased risk of falls.

Caregiver Burden and the Nonmotor Symptoms of Parkinson's Disease

Parkinson's disease has traditionally been considered as primarily a motor disorder (Chaudhuri & Schapira, 2009). It is clear however that it is the burden of the nonmotor symptomatology which impacts significantly more highly on caregiver burden and quality of life (Benavides, Alberquerque, & Chana-Cuevas, 2013; Martinez-Martin, 2011). As Parkinson's disease advances there is an almost inevitable accrual of nonmotor symptoms alongside the motor aspects of the disease. Patients as their disease progresses require increasing support and this is not infrequently provided by an informal caregiver, most typically a spouse or family member (Martinez-Martin, Forjaz, Frades-Payo, et al., 2007). The role of the caregiver while being emotionally, physically, and psychosocially demanding is also costly and time intensive. The cost of care is typically borne by the family and one survey has estimated that the average caregiver spends an average of 22h per week fulfilling their role. The caregiver has a unique and privileged view of the patient's condition and often due to symptoms of apathy, cognitive impairment, and depression can provide a more accurate appraisal of symptoms and treatment effect. It is therefore imperative that the caregiver is involved, where possible in clinical appointments and treatment decisions. During this chapter the impact of nonmotor symptoms on the caregiver will be highlighted and the need for early and continued collaboration with the caregiver reiterated. The influence of certain key nonmotor symptoms on caregiver burden will be explored in more detail and the narrative will be punctuated with carer reflections as experienced by Jon Hiseman while caring for his wife Barbara, a world renowned saxophonist.

Association between cognitive impairment and urinary dysfunction in Parkinson's disease

Urinary dysfunction (UD) is a common non-motor feature of Parkinson's disease (PD), and might be secondary to neurodegeneration involving cortical and subcortical brain areas. The possible link between UD and cognitive deficits has never been examined in frontal cortex impairment, and is still not completely understood in PD. In the present study, 94 PD patients underwent a comprehensive motor, cognitive and non-motor assessment. It was shown that 55.3% of patients reported UD, of which 17% needed specific urological treatment. Patients who reported UD performed worse on global cognition (PANDA, p = .05), visuo-constructive functions (CERAD/praxis, p = .03; and Figure Test, p = .03), and instrumental activities of daily living functions (IADL, p = .03), than patients without UD. The group with UD medication performed worse on global cognition (PANDA, p = .02) and visuo-constructive functions (CERAD/praxis, p = .05; CERAD/praxis recall, p = .05) than the UD group without medication, independent of anticholinergic treatment effect. Our findings suggest an association between cognitive impairment and UD in PD independent from symptomatic treatment.

Post-cueing deficits with maintained cueing benefits in patients with Parkinson's disease dementia

In Parkinson’s disease (PD), internal cueing mechanisms are impaired leading to symptoms like hypokinesia. However, external cues can improve movement execution by using cortical resources. These cortical processes can be affected by cognitive decline in dementia. It is still unclear how dementia in PD influences external cueing. We investigated a group of 25 PD patients with dementia (PDD) and 25 non-demented PD patients (PDnD) matched by age, sex, and disease duration in a simple reaction time task using an additional acoustic cue. PDD patients benefited from the additional cue in similar magnitude as did PDnD patients. However, withdrawal of the cue led to a significantly increased reaction time in the PDD group compared to the PDnD patients. Our results indicate that even PDD patients can benefit from strategies using external cue presentation but the process of cognitive worsening can reduce the effect when cues are withdrawn.