Impaired rTMS-induced short-term neuroplasticity in restless legs syndrome: a pilot study

Introduction: transcranial magnetic stimulation (TMS) studies in restless legs syndrome (RLS) have shown an overall pattern of disinhibition and hyperexcitability of the primary motor cortex (M1) [1]. An impaired plasticity in terms of decreased post-exercise facilitation and associative plasticitywas also hypothesized [2], although a direct demonstration using repetitive TMS (rTMS) is lacking. We tested for the first time the shortterm mechanisms of cortical rearrangement through inhibitory rTMS in patients with idiopathic RLS. Methods: using a figure-of-eight coil, motor evoked potentials (MEPs) were recorded from the right first dorsal interosseus muscle of 6 right handed RLS patients (mean age 60.5 years; IQ range 53-70) and 6 agematched healthy controls (mean age 59.5 years, IQ range 34-72). By setting the stimulus intensity at 110% of the resting motor threshold (rMT), a single session of low-frequency (1 Hz) rTMS over the left M1 was performed in the evening. The session consisted of 20 trains with 50 stimuli per train and an intertrain interval of 30 s (1,000 stimuli in total). Results: no differencewas found for rMT between the two groups. Smaller MEPs amplitude at the end of both single train and whole rTMS procedure was observed in all subjects, although this was significantly more pronounced in controls than in patients (Figure). Discussion: compared to normal individuals, RLS patients did not exhibit the short-term inhibitory rTMS-induced cortical rearrangement, suggesting an impairment of the GABA-mediated mechanisms of excitability and plasticity. This finding, although preliminary, might be viewed as a possible target of specific drugs and non-invasive brain stimulation techniques modulating the sensory-motor networks in RLS. TMS confirms to be a powerful tool in probing the neurophysiology and, indirectly, the neurochemistry of sleep disorders.