Which factors affect phenoconversion in isolated rapid eye movement sleep behavior disorder?

Aim: Isolated REM sleep behavior disorder (IRBD) is characterized by loss of the normal atonia of REM sleep. Patients with IRBD are at substantial risk of developing the synuclein-related neurodegenerative diseases (NDD). Few predictors of phenoconversion (from IRBD to NDD) have been identified such as age >65 years, hyposmia, constipation, elevated Epworth sleepiness scale (ESS). We aimed to detect rate and risk factors of phenoconversion.Method: The study designed as retrospectively. NDD was developed in 18 (27.27%) patients while NDD wasn't developed in 48 (72.73%) patients after ten years. The data of the first visit (age, gender, hyposmia, constipation, ESS, comorbidities, physical/neurological examinations, laboratory, and polysomnography) were compared between NDD (n:18) and IRBD (46) groups. The statistical program IBM SPSS Statistics Version 20.0 was used for all analyzes. The threshold for statistical significance for each test was set at 0.05. Results: Although, most first-visit data (age, gender, hyposmia, constipation, ESS, laboratory, polysomnography) were not different between NDD (n:18) and IRBD (n:48) groups, diabetes mellitus (DM) frequency (p:0.021), mean duration of DM (0.027), chest circumference (p:0.017), and hip circumference (p:0.045) were found higher in NDD than IRBD. If the risk of phenoconversion calculated by logistic regression analysis was different only in terms of DM frequency (p:0.030) [odds ratio: 4.909 (1.17-20.19)].Conclusion: The present study showed that the phenoconversion rate for ten years is 27.27%, and IRBD patients with diabetes mellitus increase the phenoconversion risk nearly five times.