Does severity of Parkinson's disease vary according to season?

In temperate climates, many factors that may influence function in Parkinson's disease (PD) vary according to season. We examined whether severity of PD, as measured by the Unified Parkinson's Disease Rating Scale (UPDRS), varied with the season of evaluation. We found no evidence for seasonal fluctuation in the UPDRS scores, suggesting that, although considerable day-to-day variation may exist in PD, there is little monthly or seasonal variation. Copyright 2004 Movement Disorder Society.