Excitatory and inhibitory mechanisms in Wilson's disease: investigation with magnetic motor cortex stimulation

We have evaluated cortical excitability in nine patients affected by Wilson's disease (WD) using transcranial magnetic (TMS) and electric (TES) cortical stimulation and central silent period (CSP) data. A clinical score was derived from the sum of scores assigned to extrapyramidal, pyramidal and cerebellar signs. All patients underwent TMS. Motor evoked potentials (MEPs) from abductor pollicis brevis (APB) and tibialis anterior (TA) muscles were recorded. MEP threshold and amplitude, central motor conduction time (CMCT), CSP threshold, CSP and peripheral silent period (PSP) duration were measured. Three patients also underwent transcranial bifocal electric cortical stimulation (TES) and MEPs were recorded from the APB muscle, and CMCT, MEP threshold and amplitude were measured. TMS MEPs were absent from relaxed muscles in six patients and from contracted muscles in three. CMCT was prolonged in six patients. APB CMCT correlated with clinical score. In three patients in whom TMS revealed abnormal or no MEP, TES MEPs were of normal threshold and amplitude. The CSP threshold was increased in seven patients, and CSP was absent in one. These results suggest an intracortical presynaptic motor dysfunction in WD.