Epidemiology of autonomic dysfunction in Parkinson's disease (Review).

Although autonomic dysfunction symptoms are commonly reported by patients with Parkinson's disease (PD) (70-90%), they are frequently under-recognized. Dysautonomia often precedes motor symptoms and can affect the quality of life (QoL) of patients with PD. The present review provides a summary of evidence on prevalence patterns, risk factors and clinical presentations from organ systems related to autonomic dysfunction. Cardiovascular symptoms include orthostatic hypotension (30-50%), supine hypertension (34-50%) and non-dipping patterns of blood pressure (83-88%). Constipation is commonly observed during the prodromal period (60%), and is observed in up to 100% of patients with PD. Genitourinary (89%) and sexual dysfunctions (52-75%) are common, although under-reported. An older age, male sex, duration of disease, severity of the disease and akinetic-rigid phenotype are directly related to overall worse dysautonomia. Genotypic variants have varying degrees of relation with autonomic symptoms; for example, the SNCA gene mutation is associated with cardiac sympathetic denervation, and PARK2 or PARK9 are related to mild effect in autonomic function. Autonomic symptoms are associated with more rapid progression of disease, the attainment of disease milestones, cognitive decline and a poorer QoL. The true prevalence of dysautonomia may be higher due to of the variability of presentation and reporting biases, and current diagnostic definitions may underestimate these non-motor symptoms. The early detection of autonomic impairment may provide time points for intervention that could modify the natural history of the disease. Future studies are required to be directed towards PD-related treatment strategies, autonomic-cognitive relationships, and the development of better animal models covering the complex pathophysiology of PD.