Subjective Cognitive Complaint in Parkinson's Disease Patients With Normal Cognition: Canary in the Coal Mine?

The objective of this study was to determine the frequency and impact of subjective cognitive complaint (SCC) in Parkinson's disease (PD) patients with normal cognition.

Patients with PD with expert consensus-determined normal cognition at baseline were asked a single question regarding the presence of SCC. Baseline (N = 153) and longitudinal (up to 4 follow-up visits during a 5-year period; N = 121) between-group differences in patients with PD with (+SCC) and without (-SCC) cognitive complaint were examined, including cognitive test performance and self-rated and informant-rated functional abilities.

A total of 81 (53%) participants reported a cognitive complaint. There were no between-group differences in global cognition at baseline. Longitudinally, the +SCC group declined more than the -SCC group on global cognition (Mattis Dementia Rating Scale-2 total score, F_1,431 = 5.71, P = 0.02), processing speed (Symbol Digit Modalities Test, F_1,425 = 7.52, P = 0.006), and executive function (Trail Making Test Part B, F_1,419 = 4.48, P = 0.04), although the results were not significant after correction for multiple testing. In addition, the +SCC group was more likely to progress to a diagnosis of cognitive impairment over time (hazard ratio = 2.61, P = 0.02). The +SCC group also demonstrated significantly lower self-reported and knowledgeable informant-reported cognition-related functional abilities at baseline, and declined more on an assessment of global functional abilities longitudinally.

Patients with PD with normal cognition, but with SCC, report poorer cognition-specific functional abilities, and are more likely to be diagnosed with cognitive impairment and experience global functional ability decline long term. These findings suggest that SCC and worse cognition-related functional abilities may be sensitive indicators of initial cognitive decline in PD. © 2020 International Parkinson and Movement Disorder Society.