Cardiac denervation and dysautonomia in Parkinson's disease: a review of screening techniques.

Parkinson's disease (PD) has classically been characterized by features of motor dysfunction, but these may manifest only after the nigrostriatal system has incurred significant damage. However, recent evidence suggests that cardiac sympathetic denervation occurs early on in PD. This may trigger a shift in physicians' attention to features of cardiovascular dysautonomia and allow for the evolution of earlier screening techniques. MIBG and PET (6F-DA) scans have demonstrated the functional loss of postganglionic sympathetic cardiac neurons, while immunohistochemical stains have revealed signs of morphological degeneration. Given this information, various screening techniques have been proposed, though most are particular to PD patients with orthostatic hypotension (OH). This is a considerable drawback given that the prevalence of OH in PD patients is estimated to be 41%. We present the argument that a shift in focus is needed; investigators should look for other manners by which to screen patients that are not reliant upon blood pressure. In our point of view, the problem with using blood pressure as a measurement is that it can be affected by many other factors unrelated to cardiac denervation. This may be why many patients with PD cannot be detected using these techniques. In order to make further progress on this front, we believe that investigators should start looking for variables that are more purely dependent upon cardiac denervation. We give one possible example of such a variable in this paper using heart transplant patients as a model.