Severity of idiopathic rapid eye movement sleep behavior disorder correlates with depression and alexithymia

Depression and alexithymia often accompany early stages of Parkinson's disease (PD). However, these symptoms in idiopathic rapid eye movement sleep behavior disorder (iRBD) remain incompletely understood. The aim of this study was to compare depression and alexithymia between iRBD patients and healthy controls, and to evaluate the association between clinical RBD severity and severity of depression and alexithymia.

Polysomnography-confirmed iRBD patients (n = 86) and healthy controls (n = 74) were enrolled. Clinical RBD severity was assessed using the RBD questionnaire-Hong Kong (RBDQ-HK). Depression and alexithymia were evaluated by the Beck Depression Inventory (BDI) and the 20-item Toronto Alexithymia Scale (TAS-20), respectively. Multivariate linear regression analysis was performed with adjustments for several covariates to determine the correlations between RBD severity and severity of depression and alexithymia.

BDI scores were significantly higher in the iRBD group (10.6 ± 7.3) than in healthy controls (8.2 ± 6.0, p = 0.024). Higher total RBDQ-HK scores were associated with more severe depression in iRBD patients, even after controlling for confounding variables. iRBD patients exhibited significantly higher TAS-20 scores (45.7 ± 10.4) than healthy controls (42.1 ± 9.8, p = 0.026). Total RBDQ-HK scores were positively correlated with TAS-20 scores independent of BDI scores.

Patients with iRBD were more depressed and had more severe alexithymia than healthy controls. Notably, as the clinical severity of RBD increased, both depression and alexithymia worsened.