Alteration of circadian sleep-wake rhythm and salivary melatonin secretion in idiopathic/isolated REM sleep behavior disorder: preliminary evidence

Objective/Background Idiopathic/isolated REM sleep behavior disorder (iRBD) is widely regarded as an early sign of neurodegeneration leading to synucleinopathies. While circadian rhythm alterations in iRBD have been preliminarily demonstrated, evidence on melatonin secretion patterns in this clinical condition is limited. To address this knowledge gap, this exploratory study aimed to integrate salivary melatonin measurement with actigraphic monitoring in individuals with iRBD and age-matched healthy controls (HC) under real-life conditions. Methods Participants diagnosed with iRBD and HC underwent clinical evaluation and wore an actigraph for seven days and nights. Salivary melatonin concentrations were measured at five time points during the last night of recording. Comparative analyses were conducted on clinical data, actigraphic parameters, and melatonin levels between the two groups. Results iRBD participants (n = 18) showed greater motor (p < .01) and non-motor symptoms (p < .001), alongside disruptions in circadian sleep-wake rhythms compared to HC (n = 10). Specifically, actigraphy revealed a delayed central phase measurement (p < .05), reduced activity during most active hours (p < .001), and decreased relative amplitude (p < .05). Total salivary melatonin concentration was significantly lower in iRBD (p < .05), with a slight but non-significant phase delay in dim light melatonin onset. Conclusions This exploratory study highlights a dysregulation of circadian sleep-wake rhythms coupled with reduced melatonin secretion in iRBD. Future research could add to these preliminary findings to evaluate novel treatment approaches to regulate the sleep-wake cycle and elucidate the implications of circadian dysregulation in the conversion from iRBD to neurodegeneration.