In vivo study indicating loss of intracortical inhibition in tumor-associated epilepsy.

Transcranial magnetic stimulation was performed in 2 patients with focal motor seizures in the right hand caused by a circumscribed tumor process affecting the left precentral gyrus. In both cases, paired-pulse transcranial magnetic stimulation showed a loss of intracortical inhibition for interstimulus intervals of 2 to 4msec that was replaced by an enormous facilitation in the lesioned hand motor cortex. The uniform impairment of inhibitory mechanisms in epileptogenic tumors with different histologies suggests a common, nonspecific cause of tumor-related epileptogenesis.