Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Neuroscience

Supervisor

Penny MacDonald

Abstract

Cognitive impairment is the most common non-motor symptom in Parkinson’s disease (PD), affecting up to one-third of early-stage patients. However, the cognitive profile in early PD remains unclear due to the use of heterogenous samples of disease severity, small sample sizes, and the inclusion of medication effects. This study aims to characterize cognitive deficits in early PD using a large, drug-naive sample. This study examined performance on the Montreal Cognitive Assessment and the Hopkins Verbal Learning Test from the Parkinson’s Progression Markers Initiative dataset (n= 643 patients with PD; n= 240 healthy controls). Patients were restricted to ≤ 12 months of disease duration and had not begun chronic dopaminergic therapy. Bayesian analyses of covariance showed Group effects in global cognition, executive function, recall, and retrieval between PD patients and controls. This suggests that early PD patients exhibit multidomain cognitive deficits, including global cognition, executive function, and memory.

Summary for Lay Audience

Parkinson’s disease (PD) is an age-related, neurodegenerative disorder. PD is commonly recognized for its motor symptoms, whereby patients have trouble in walking, balance, talking, and posture amongst other symptoms. However, patients with PD also experience non-motor symptoms (NMS) that have devastating effects on quality of life. Cognitive impairment is the most common NMS in PD, affecting up to one-third of early-disease patients. Cognitive impairment hinders the ability to think, reason, use logic, remember, and perform other functions that are used in day-to-day living. Although widely studied, the cognitive profile of early PD remains largely unclear. This is due to variability in the disease severity amongst patients in a sample, smaller study samples, and patients taking medication to manage their motor symptoms which can have a side effect on boosting or worsening specific cognitive functions. Thus, it is important to study the profile of cognition, specifically which domains are affected disproportionately, in early PD using a larger, drug-naïve group of patients.

The objective of this study was to create a better profile of cognitive impairment in early PD. We used a large, drug-naïve sample of patients restricted to less than 12 months into disease duration to reduce variability in our sample. We used two different clinical measures to assess several domains of cognition: Global cognition, Executive, Memory Recall, Memory Retrieval, Attention, Learning, Language, Visual abilities, and Orientation to time and space. We compared performance on these measures across early-disease patients with PD and healthy elderly controls. We found patients with PD showed worsened performance on outcome measures of Global cognition, Executive, Memory Recall, and Memory Retrieval. Thus, the profile of cognitive impairment in PD in early disease seems to be multidomain impairment in global cognition, executive functions, and memory impairments.

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