A systematic review on autonomic dysfunctions in Parkinson’s disease

Parkinson's Disease (PD) is a neurodegenerative disorder characterized by a complex array of motor and non-motor symptoms. Abundant experimental research has explored the behavioral and neural correlates of these symptoms but it is so far unclear if and how autonomic (dys-)functions can modulate or even precede PD symptom progression. Here, we systematically reviewed the evidence on autonomic dysfunction in PD, synthesizing findings from more than 2000 individuals with PD across 47 studies that met eligibility criteria. Most studies (85%) assessed cardiovascular activity, whereas dysfunctions in breathing (15%), skin (9%), sleep (15%), and circadian (9%) regulations were investigated less frequently. Overall, we find strong convergence for an imbalance of sympathetic and parasympathetic activity; baroreflex, skin (e.g., pilomotor control) and olfactory (e.g., hyposmia) dysfunctions; a strong link with sleep disorders (e.g., idiopathic REM sleep behavior disorder); a weaker circadian regulation of cardiovascular functions; and central alterations in the breathing control network (engaging the insula and brainstem).