Autonomic dysfunction in PD: A window to early detection?

It has been suggested that autonomic dysfunction constitutes a biomarker for early detection of the disease process in Parkinson disease (PD). Recent findings based on cardiac sympathetic and striatal dopaminergic imaging in the same patients indicate that this view is overly simple. Although evidence of cardiac sympathetic denervation is associated with other non-motor manifestations such as anosmia, REM behavior disorder, dementia, baroreflex failure, and orthostatic hypotension (OH), across individual patients the severities of OH and of the cardiac sympathetic lesion (indicated by thoracic 6-[18F]fluorodopamine PET scanning) are unrelated to the severity of the putamen dopaminergic lesion (indicated by brain 6-[18F]fluorodopa PET scanning). Moreover, whereas cases have been reported with neuroimaging evidence of cardiac sympathetic denervation several years before motor onset of PD, in other cases loss of cardiac sympathetic innervation progresses approximately concurrently with the movement disorder or can even occur as a late finding. Bases for independent sympathetic noradrenergic and striatal dopaminergic lesions in Lewy body diseases remain poorly understood. In elderly patients with unexplained OH or other evidence of autonomic failure, it is reasonable for clinicians to look for subtle signs of parkinsonism, such as masked facies, cogwheel rigidity, and shuffling gate.