The Epidemiology of Nonmotor Symptoms in Parkinson's Disease (Cohort and Other Studies).

Nonmotor symptoms (NMS) of Parkinson's disease (PD) were recognized by James Parkinson himself and are now considered to be an integral part of PD. While clinical assessment had focused on prevalence and severity of individual NMS such as dementia and depression, work in the last decade has concentrated on global or holistic assessment of NMS using validated tools such as the NMS questionnaire and NMS scale. These studies from cohorts of varying sizes have allowed comparison of NMS across different disease stages, duration, age, and ethnicity in PD. The data also allow exploration of the concept of the nonlinear relationship of NMS to disease duration of PD and motor stages as well as nonmotor subtypes of PD. In this chapter, these aspects of epidemiological studies of NMS in PD cohorts are described.