Abnormal Intracortical Functions in Parkinson's Disease with Rapid Eye Movement Sleep Behaviour Disorder

Rapid eye movement sleep behaviour disorder (RBD) is considered to be one of the most frequent and important prodromal symptoms of Parkinson's disease (PD). We aimed to study the neurophysiological abnormalities in patients of PD-RBD and PD without RBD (PD-nRBD) using transcranial magnetic stimulation (TMS).

Twenty patients each of PD-RBD and PD-nRBD were included in the study in addition to 20 age and gender-matched healthy controls. RBD was identified using the RBD screening questionnaire (RBDSQ). All the subjects were evaluated with single and paired-pulse TMS and parameters such as resting motor threshold (RMT), central motor conduction time (CMCT), silent period (SP), short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were recorded.

The mean age of the controls and PD patients with and without RBD was comparable. There were no significant differences in RMT, CMCT and silent period between the two patient groups. SICI was present in all the three groups with significant inhibition noted in PD-RBD group (p < 0.001). ICF was absent in patients of PD-RBD (0.19 ± 0.11) and PD-nRBD (0.7 ± 0.5) when compared to controls (1.88 ± 1.02) with profound impairment in patients with PD-RBD (p < 0.001). The mean MoCA score was found to be significantly different in all the three groups with a worse score in patients with RBD (23.10 ± 2.55; p < 0.001).

PD-RBD patients have significantly greater inhibition and reduced intracortical facilitation suggesting enhanced GABAergic and reduced glutaminergic transmission. These abnormalities may underlie the different pathophysiological process observed in these patients.