Follow-up study of cardiac 123I-MIBG scintigraphy in idiopathic REM sleep behavior disorder

Background: Cardiac ¹²³I‐metaiodobenzylguanidine (¹²³I‐MIBG) uptake in patients with idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD) is markedly reduced, as in Parkinson’s disease (PD). Methods: We performed ¹²³I‐MIBG scintigrams on patients with iRBD and PD. After the initial ¹²³I‐MIBG scintigram, we retested subjects after a mean of 2.8 years. Results: The delayed heart‐to‐mediastinum (H/M) ratio of cardiac ¹²³I‐MIBG uptake was not significantly reduced between the first and second study in either group (P = 0.050, P = 0.091, respectively) . Follow‐up imaging revealed a mean decline of 4.21 ± 9.06% or 6.40 ± 19.02% in the delayed H/M ratio in those with iRBD or PD, respectively. Conclusions: The ¹²³I‐MIBG uptake findings might indicate progression early in the course of iRBD or PD, but the progression is heterogeneous and independent of development of motor symptoms.