Objective: To assess the presence of increased REM-related motor activity during sleep, by questionnaires for REM sleep behavior disorder (RBD), in subjects with "isolated" REM sleep without atonia (RWA).
Subjects and Methods: Two-hundred-and-forty-nine patients were consecutively enrolled, with age ≥18 years, sharing bedroom with a roommate, and without a severe health, neurologic or cognitive problem. Motor activity during sleep was assessed by means of the RBD Screening Questionnaire (RBDSQ) and the RBD questionnaire-Hong Kong (RBDQ-HK). A video-polysomnographic recording was obtained and the REM Atonia Index was computed. Thirteen subjects were diagnosed to have RBD while the remaining 236 were subdivided into two subgroups: 34 subjects with "low" (<0.8) and 202 subjects with "high" Atonia Index (≥0.8).
Results: RBDSQ and RBDQ-HK were both higher in subjects with low Atonia index than in those with high Atonia Index, as well as number of drugs taken and number of comorbidities. No effect of antidepressant use was found on Atonia index and a multiple regression analysis showed that Atonia Index was significantly (inversely) correlated only with the behavioral score obtained with the RBDQ-HK.
Conclusion: Our study shows that individuals with isolated RWA have an increased motor activity/behavioral pattern during sleep, although this activity does not allow to diagnose RBD. Our findings broaden the spectrum of RBD and the condition that we have identified should be better characterized in order to understand its eventual development into fully blown RBD or not.