Abstract
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.