Seasonal variations of nonmotor symptoms in patients with Parkinson's disease in Southeast China

BACKGROUND: Studies suggest seasonal fluctuations of symptoms in Parkinson's disease (PD) patients in Western countries. However, the association between seasonal change and variation in nonmotor symptoms (NMS) in Chinese PD patients is unclear. Here, we studied whether there is a change rule with annual cycle with severity of NMS for patients with PD in Southeast China. METHODS: We studied 1005 PD patients between April 2008 and October 2020. Patients were classified into four seasons according to the 24 Chinese solar terms, based on assessment date. We compared comprehensive NMS scales and polysomnography parameters among groups and conducted further analysis of disease severity. RESULTS: Among the 1005 patients studied, the mean age was 64.2 ± 9.7 years and 569 (56.6%) of them were men. Relative to the summer group, patients assessed during winter had higher Scales for Outcomes in Parkinson's disease-Autonomic Dysfunction (SCOPA-AUT) scores (P = 0.045). The sleep efficiency factor scores of Pittsburgh Sleep Quality Index in patients were higher during spring than summer (P = 0.009). Among patients who completed polysomnography during the same period (n = 135), compared with summer follow-ups, we observed a higher percentage of NREMS1 in winter and spring follow-ups (P = 0.042, P = 0.011), a higher NREMS1 time in spring follow-ups (P = 0.0024), a lower NREMS2 time in winter follow-ups (P = 0.007), and a higher percentage of phasic rapid eye movement (REM)-sleep without atonia in autumn and winter follow-ups (P = 0.026 and P = 0.020, respectively). In a subset of patients with PD and REM sleep behavior disorder (RBD; n = 182), those visited during winter had higher scores for RBD questionnaire-Hong Kong and its factor 1 (dream-related sub-score) than those visited during summer (P = 0.034, P = 0.020). We observed similar findings for SCOPA-AUT and sleep efficiency factor scores in early stage patients in subgroup analysis. CONCLUSIONS: PD patients assessed for follow-up during summer showed less severe symptoms of autonomic dysfunction and RBD symptoms than those assessed in winter, and less sleep disturbance than those in spring and winter, suggesting that seasonal change and NMS fluctuation are related, especially in patients with early stage PD.