Cortical involvement in the sensory and motor symptoms of primary restless legs syndrome

Abstract 

Background

Restless legs syndrome (RLS) is characterized by closely interrelated motor and sensory disorders. Two types of involuntary movement can be observed: periodic leg movements during wakefulness (PLMW) and periodic leg movements during sleep (PLMS). Basal ganglia dysfunction in primary RLS has often been suggested. However, clinical observations raise the hypothesis of sensorimotor cortical involvement in RLS symptoms. Here, we explored cortical function via movement-related beta and mu rhythm reactivity.

Methods

Twelve patients with idiopathic, primary RLS were investigated and compared with 10 healthy subjects. In the patient group, we analyzed event-related beta and mu (de)synchronization (ERD/S) for PLMS and PLMW during a suggested immobilization test (SIT). An ERD/S analysis was also performed in patients and controls during self-paced right ankle dorsal flexion at 8:30PM (i.e., the symptomatic period for patients) and 8:30AM (the asymptomatic period).

Results

Before PLMS, there was no ERD. Intense ERS was recorded after PLMS. As with voluntary movement, cortical ERD was always observed before PLMW. After PLMW, ERS had a diffuse scalp distribution. Furthermore, the ERS and ERD amplitudes and durations for voluntary movement were greater during the symptomatic period than during the asymptomatic period and in comparison with healthy controls, who presented an evening decrease in these parameters. Patients and controls had similar ERD and ERS patterns in the morning.

Conclusion

On the basis of a rhythm reactivity study, we conclude that the symptoms of RLS are related to cortical sensorimotor dysfunction.

Abbreviations used: ERD, event-related desynchronization, ERS, event-related synchronization, PMBS, post-movement beta synchronization, RLS, restless legs syndrome, AT, anterior tibialis muscle, SPM, self-paced movement, PLMS, periodic leg movements during sleep, PLMW, periodic leg movements during wakefulness, F, frontal, FC, frontocentral, C, central, CP, centroparietal, P, parietal

Keywords: Restless legs syndrome, Electrocortical rhythms, Sensorimotor integration, Cortical involvement, Involuntary movements, Electroencephalography