The prolonged cortical silent period in patients with Huntington's disease

Objectives: In a group of patients with Huntington's disease and age-matche d controls, we studied the cortical silent period (SP) elicited by single t ranscranial magnetic stimulation (TMS) pulses. Methods: We measured the area of the pre-stimulus electromyographic (EMG) a ctivity, the area of the motor evoked potentials (MEPs) and the duration of the SP induced by stimuli delivered at an intensity of 150% of motor thres hold with a round coil placed over the vertex. We determined the cortical S P by sampling only the 5 traces containing the shortest SPs and by collecti ng 10 consecutive unselected traces without selecting trials. Results: Patients and controls had normal EMG background areas, and MEP lat encies and areas. Whereas data measured from selected trials gave a normal duration of the SP (patients, 154 +/- 58 ins, controls, 166 +/- 22 ms), dat a from unselected trials yielded a significantly longer SP duration in pati ents than in controls (356 +/- 251 vs. 159 +/- 44 ms) and also a lamer vari ance and range. Conclusions: We conclude that in Huntington's disease, an abnormal cortical SP is best sought by collecting unselected consecutive traces. We suggest that the prolonged SP in HD originates from a dysfunction of the mechanisms controlling the restart of voluntary movement after TMS. (C) 2001 Elsevier Science Ireland Ltd. All ri-hts reserved.