Non-motor features of Parkinson's disease: depression and dementia.

Parkinson's disease (PD) is the second most common neurodegenerative disease and primarily considered as a movement disorder defined by the presence of motor symptoms, such as bradykinesia, tremor and rigidity. However, it is nowadays widely recognized that in addition there is impairment of cognitive function, mood and the autonomic nervous system in a high percentage of PD patients, which is sometimes even more harming quality of life. These symptoms not only occur during the course of the disease but may even precede the onset of motor symptoms. Typical examples of non-motor features of PD are depression, constipation, REM sleep behaviour disorder, and hyposmia.