Impact of sleep quality on cognitive functions in Parkinson’s disease

BACKGROUND: Sleep disorders lead to cognitive deficits in healthy people and are thought to have significant impact on cognition in Parkinson’s disease (PD). OBJECTIVE: To study the sleep pattern and its relationship to cognitive functioning in non-demented PD cohort. MATERIALS AND METHODS: Sleep was evaluated by Pittsburg Sleep Quality Index (PSQI) in a cohort of PD patients. Comprehensive assessment of cognitive domains including attention, executive functions, short/long-term verbal memory, visual memory, and visuospatial functioning was done by battery of neuro-physiological tests on patients in “ON” state. Based on the component PSQI sleep score, patients were grouped as having "good quality sleep" (PSQI score ≤ 5) or "poor quality sleep" (PSQI score > 5). The demographic profile, disease characteristics, treatment, and cognitive tests were then compared between the two groups. RESULTS: Of 130 patients with diagnosis of PD, 85 patients were included. 63 (74.1%) had good sleep quality while 22 (25.9%) had poor sleep quality. Mean age and disease characteristic were comparable between two groups except that females had statistically significant (P = 0.001) poor sleep quality as compared to men. Poor sleep quality had significant effect on cognitive functions including generativity, inhibition, set-shifting, perseveration, and attention but there was no impact of sleep on verbal memory, visual memory, and visuospatial abilities. CONCLUSION: PD patients with poor sleep quality on PSQI questionnaire should be carefully screened for presence of any cognitive impairment especially executive impairment, as these two may be inter-related. Intervention to improve sleep would have far reaching benefits to improve the quality of life of PD patients.