Clinical characteristics and phenoconversion in isolated REM sleep behavior disorder: a prospective single-center study in Korea, compared with Montreal cohort

Study Objectives: Isolated rapid eye movement sleep behavior disorder is a prodromal synucleinopathy, but its conversion rate and subtypes can vary among different cohorts. We report the clinical characteristics and phenoconversion rate of the large single-center isolated rapid eye movement sleep behavior disorder cohort in Korea and compared it to the Montreal cohort. Methods: This prospective cohort study examined 238 patients with polysomnography confirmed isolated rapid eye movement sleep behavior disorder from Seoul National University Hospital (SNUH) who completed at least 1 follow-up evaluation. We compared the baseline and phenoconversion data of the SNUH cohort to those of 242 isolated rapid eye movement sleep behavior disorder patients in the Montreal cohort. Results: In the SNUH cohort, age at rapid eye movement sleep behavior disorder diagnosis was similar (66.4 +/- 7.8 vs 65.6 +/- 8.4, P = .265), but the proportion of men was lower (63.0% vs 74.0%, P = .01), and the duration of follow-up was shorter than that in the Montreal cohort (3.7 +/- 2.0 vs 4.8 +/- 3.6 years, P < .001). During follow-up, 34 (11.8%) patients in the SNUH cohort converted to neurodegenerative disease: 18 (52.9%) to Parkinson's disease, 9 (26.5%) to dementia with Lewy bodies, and 7 (20.6%) to multiple system atrophy. The conversion rate in the SNUH cohort was 15% after 3 years, 22% after 5 years, and 32% after 7 years, which was significantly lower than that of the Montreal cohort (log-rank test, P = .002). Among phenoconversion subtype, fewer patients in the SNUH group than in the Montreal group converted to dementia with Lewy bodies (Gray's test P = .001). Conclusions: Through a comparative analysis between the SNUH and Montreal cohorts, we identified a significant difference in phenoconversion rates, particularly for dementia with Lewy bodies patients. These findings underscore the importance of further research into the underlying factors, such as racial and geographical factors contributing to such disparities.