Effects of Cognitive Performance and Affective Status on Fatigue in Parkinson's Disease

Background: Fatigue is a common non-motor symptom in Parkinson's disease (PD) and is typically assessed via self-reported questionnaires such as the Parkinson's Fatigue Scale (PFS). The PFS captures the presence of subjective experience of physical fatigue as well as its impact on daily functioning. Objectives: We aimed to investigate whether different variables (cognition, neuropsychiatric symptoms, disease-related measures) are associated with the experience of physical fatigue in comparison to fatigue affecting daily functioning. Method: Sixty-two non-demented PD patients were evaluated through questionnaires assessing fatigue, daytime sleepiness, apathy, depression, anxiety, and cognition. Items of fatigue were classified and summarized into two index variables measuring either the subjective experience of physical fatigue or the impact of fatigue on daily functioning. Linear regression with a stepwise elimination procedure was conducted to select the significant predictors for each index variable separately. Results: Subjective experience of physical fatigue (Model 1; r(2) = 0.46; p <0.01) was significantly associated with higher levels of depression (b =0.07; p <0.01), anxiety (b =0.03; p <0.05), and lower performances in verbal episodic memory (b =-0.16; p <0.05). Fatigue affecting daily functioning (Model 2; r(2) = 0.44; p <0.05) was significantly related to higher levels of depression (b = 0.07; p < 0.01), anxiety (b = 0.03; p > 0.05), and lower motor functioning (b = 0.01; p = 0.05). Conclusions: In conclusion, our work supports associations between fatigue and other neuropsychiatric symptoms in PD and extends prior work suggesting that motor disturbances are specifically linked to fatigue-related impairment of daily functioning, but not to the subjective experience of physical fatigue.