Cardiac denervation in patients with Parkinson disease.

More than 40 neuroimaging studies have reported evidence for loss of sympathetic noradrenergic nerves in PD. Cardiac sympathetic denervation is virtually universal in patients with PD and neurogenic orthostatic hypotension. About one half of patients with PD who do not have orthostatic hypotension also have evidence for loss of noradrenergic innervation. The loss progresses over years, in a pattern suggesting "dying-back". Because patients with familial PD from mutation of the gene encoding alpha-synuclein or from triplication of the normal gene have low myocardial concentrations of 6-[18F]fluorodopamine-derived radioactivity, cardiac sympathetic denervation seems linked etiologically with alpha-synucleinopathy. Baroreflex-cardiovagal failure and cardiac sympathetic denervation can occur before onset of the movement disorder, suggesting that neurocardiologic testing might provide a biomarker for detecting presymptomatic or early PD and for following responses to putative neuroprotective treatments.