Reduced cardiac 123I-MIBG scintigraphy in idiopathic REM sleep behavior disorder.

Idiopathic REM sleep behavior disorder (RBD) may represent prodromal synucleinopathies. We report markedly reduced cardiac (123)I-metaiodobenzylguanidine uptake, consistent with the loss of sympathetic terminals, in idiopathic RBD. We also demonstrate that this reduction is of the same magnitude as that found in patients with Parkinson disease. The results are consistent with the hypothesis that idiopathic RBD in older patients is a forme fruste of Lewy body disease.