Neuroimaging evidence indicating cardiac sympathetic denervation in the Lewy body (LB) synucleinopathy Parkinson disease (PD) and generally intact innervation in the non-LB synucleinopathy multiple system atrophy (MSA) was first reported using 18F-dopamine (18F-DA) positron emission tomography (PET) imaging [1]. Numerous studies since then, mainly using 123I-metaiodobenzylguanidine (123I-MIBG) single-photon emission computed tomographic (SPECT) scanning, have confirmed these findings. Of 21 studies in English on this topic involving at least 50 patients, all 21 have reported a significant group difference in the direction of cardiac noradrenergic deficiency in PD (Table 1).

The issue of whether cardiac sympathetic neuroimaging can aid the differential diagnosis of PD vs. MSA seems settled, to the extent that it can be settled. 123I-MIBG SPECT scanning for this purpose has been approved for several years in Europe and Asia. In the United States, however, 123I-MIBG SPECT scanning is rarely done for this indication, due to lack of reimbursement by third-party payers. Cardiac PET neuroimaging is conduced only in research settings.