Inhibitory and excitatory circuits of cerebral cortex after ischaemic stroke: prognostic value of the transcranial magnetic stimulation.

The motor cortex excitatory responses and inhibitory effects after transcranial magnetic stimulation were studied in 20 patients with hemiparesis after ischaemic stroke in the MCA territory within 24 hours from the beginning of the symptomatology, in order to evaluate prognostic utility of these techniques and to compare they with the conventional MEP examination. Central motor conduction time was abnormal in two patient. Ipsilateral cortico-cortical inhibition was decreased after stimulation of the ischaemic motor cortex in all patients; the duration of the silent period was prolonged in 15 patients, whereas the resting threshold for responses to magnetic stimulation was abnormal in 8 patients. Only this last finding was constantly associated with a poor motor recovery; therefore the patients with preserved motor threshold reached a good motor function in the following months. The motor cortex threshold measurement is easily performed and the most sensitive parameter in our group of patients with hemispheric infarct. Our study suggested that the evaluation of the modifications in the intrinsic excitatory properties rather than in the inhibitory cortical circuits may offer a prognostic tool for predicting functional outcome following ischaemic stroke.