Asymmetry of cortical excitability revealed by transcranial stimulation in a patient with focal motor epilepsy and cortical myoclonus.

Motor cortex excitability was analyzed with transcranial stimulation in a patient with motor focal epilepsy and cortical myoclonus originating from the right motor cortex. The motor threshold to single transcranial magnetic shocks, but not to electric stimuli, was higher in the epileptic motor cortex than the normal left motor cortex. Single magnetic shocks elicited a short cortical silent period (50 ms) in the epileptic motor cortex. Paired magnetic stimuli also showed reduced cortico-cortical inhibition. These findings reveal an asymmetry in cortical excitability presumably due to impaired inhibition in the epileptic motor cortex.