To investigate whether the increased urge to move the legs in restless legs syndrome (RLS) corresponds to an electrophysiological phenomenon and whether motor excitability or behavior is influenced by the treatment with a dopamine agonist. We examined 10 patients who had RLS with transcranial magnetic stimulation (TMS) before and during treatment with the dopamine agonist cabergoline. Results were compared with data obtained from healthy subjects. Inhibitory mechanisms were explored by measurement of the cortical silent period (cSP). Recordings were obtained from the right anterior tibial muscle. Clinical severity of RLS was rated using the International Restless Legs Syndrome Study Group Rating Scale (IRLSSGRS). During therapy with cabergoline, all patients reported a significant improvement of RLS symptoms. Before medication, patients showed a significant shortening of cSP compared with healthy subjects. After 14 days of treatment with cabergoline, cSP normalized in RLS patients; 90 days after the start of daily cabergoline, cSP tended to shorten again, whereas RLS symptoms further improved. There was no correlation between cSP duration and IRLSSGRS results. There were no differences in patient and control motor thresholds. These thresholds remained unchanged during treatment with cabergoline. RLS patients have a disturbance of inhibitory neurons that can temporarily be reversed with a dopamine agonist. However, the cSP does not correlate with the clinical symptoms.
