Montreal Cognitive Assessment Predicts the Short‐Term Risk of Lewy Body Disease in Isolated REM Sleep Behavior Disorder with Reduced MIBG Scintigraphy

BACKGROUND: Long‐term follow‐up of isolated rapid eye movement (REM) sleep behavior disorder (IRBD) patients reveals a high risk of α‐synucleinopathies. OBJECTIVE: We explored the early clinical predictive factors of phenoconversion from IRBD to Parkinson's disease (PD) or dementia with Lewy bodies (DLB). METHODS: We assessed baseline office‐based cognitive test scores (Montreal Cognitive Assessment [MoCA‐J], Mini‐Mental State Examination [MMSE], and Frontal Assessment Battery [FAB]), motor function, and olfactory function in 36 consecutive polysomnography (PSG)‐confirmed IRBD patients with reduced metaiodobenzylguanidine (MIBG) accumulation. PD or DLB was confirmed by medical chart review retrospectively. RESULTS: Of 36 IRBD patients, 19 (n = 19, 52.8%) with abnormal MoCA‐J score (< 26) had significantly lower scores in trail making B, phonetic verbal fluency sub‐items in the executive domain, and in delayed recall in the memory domain. In total, 12 (33.3%) patients developed PD or DLB; seven of 12 patients (58.3%) developed DLB at a mean follow‐up period of 6.8 years. In the normal MoCA‐J group (n = 17, 47.2%), two patients developed PD, but none developed dementia. Furthermore, in the abnormal MoCA‐J group, seven patients developed DLB and three developed PD without dementia. The phenoconverter group had significantly lower scores in delayed recall in the memory domain compared to the disease‐free group. Cox hazard analysis showed that MoCA‐J was superior to MMSE. CONCLUSIONS: Among IRBD patients with reduced cardiac MIBG accumulation, MoCA‐J score of <26 (Mild Cognitive Impairment‐Lewy body) and a low sub‐item score for delayed recall predicted short‐term progression to probable DLB.