Meta-analyses on prevalence of selected Parkinson's nonmotor symptoms before and after diagnosis.

Background: Nonmotor symptoms are common among patients with Parkinson's disease (PD) and some may precede disease diagnosis.

Methods: We conducted a meta-analysis on the prevalence of selected nonmotor symptoms before and after PD diagnosis, using random-effect models. We searched PubMed (1965 through October/November 2012) for the following symptoms: hyposmia, constipation, rapid eye movement sleep behavior disorder, excessive daytime sleepiness, depression, and anxiety.