Neurophysiological study of corticomotor pathways in restless legs syndrome

Objective: To test the variations in cerebral motor excitability in patients with primary restless legs syndrome (RLS) by using electrophysiological techniques. In RLS patients periodic legs movements (PLMs) in sleep and wake have been described and it is hypothesised that PLMs result from a sleep-related disinhibition of descending central motor inhibitory pathways. Moreover, in primary RLS, these modifications are still debated. Methods: In 15 patients with primary RLS, transcranial magnetic stimulation (TMS) was carried out using several paradigms, particularly paired pulse TMS with short interstimulus intervals (ISI) in abductor digiti minimi (ADM) and tibialis anterior (TA) muscles. Results: Short ISI paired TMS showed a significant decrease in inhibition and increase in facilitation in ADM muscles. This result was even more evident in TA muscles of patients as compared to the controls and these modifications were more evident in the limbs which were more affected by PLM. Moreover, intracortical (corticocortical) inhibition (ICI) and intracortical facilitation (ICF) unchanged their biphasic time course. Conclusions: In our study the changes in short paired-pulse ICI and ICF revealed the presence of an altered excitability of central motor pathways, with good correlation with asymmetric distribution of symptoms.