Subjective cognitive decline predicts future deterioration in cognitively normal patients with Parkinson's disease

Increasing evidence suggests that subjective cognitive decline (SCD) is a potential predictor of future cognitive decline or dementia. We investigated whether SCD in patients with Parkinson's disease (PD) is a predictor of future cognitive decline. Forty-six cognitively normal patients with PD were selected using comprehensive neuropsychological tests, and classified depending on the presence (PD-SCD⁺, n= 25) or absence of SCD (PD-SCD^-, n= 21). After a mean follow-up of 2.4 years, we repeated the cognitive assessments with the same subjects. The clinical characteristics and cognitive performance of the 2 groups did not differ at baseline. At the follow-up assessment, 11 patients in the PD-SCD⁺ group (44.0%) and 2 in the PD-SCD^- group (9.5%) were diagnosed with mild cognitive impairment (MCI), and the PD-SCD⁺ patients showed more rapid decline in semantic fluency and visuospatial memory tasks than those in the PD-SCD^- group. A multivariate logistic regression analysis showed that presence of SCD (odds ratio, 8.378; 95% confidential interval, 1.472-47.683, p= 0.017) and higher Unified PD Rating Scale motor score of 20 or more (odds ratio, 4.539; 95% confidential interval, 1.004-20.528; p= 0.049) were risk factors for incident MCI. Present results demonstrate that SCD in cognitively normal patients with PD is an independent risk factor for incident MCI and acts as a predictor for future cognitive decline.