Non-motor symptoms in Parkinson's disease

Although still considered a paradigmatic movement disorder, Parkinson's disease (PD) is associated with a broad spectrum of non-motor symptoms. These include disorders of mood and affect with apathy, anhedonia and depression, cognitive dysfunction and hallucinosis, as well as complex behavioural disorders. Sensory dysfunction with hyposmia or pain is almost universal, as are disturbances of sleep-wake cycle regulation. Autonomic dysfunction including orthostatic hypotension, urogenital dysfunction and constipation is also present to some degree in a majority of patients. Whilst overall non-motor symptoms become increasingly prevalent with advancing disease, many of them can also antedate the first occurrence of motor signs - most notably depression, hyposmia or rapid eye movement sleep behaviour disorder (RBD). Although exact clinicopathological correlations for most of these non-motor features are still poorly understood, the occurrence of constipation, RBD or hyposmia prior to the onset of clinically overt motor dysfunction would appear consistent with the ascending hypothesis of PD pathology proposed by Braak and colleagues. Screening these early non-motor features might, therefore, be one approach towards early 'preclinical' diagnosis of PD. This review article provides an overview of the clinical spectrum of non-motor symptoms in PD together with a brief review of treatment options.