Navigated transcranial magnetic stimulation to measure motor evoked potentials in a child with hemispheric polymicrogyria and focal epilepsy.

Malformations of cortical development such as polymicrogyria can cause medically refractory epilepsy. Epilepsy surgery (hemispherotomy) can be a good treatment option. In recent years, navigated transcranial magnetic stimulation (nTMS), a noninvasive brain mapping technique, has been used to localize the eloquent cortex for presurgical evaluation of patients with epilepsy. In the present case study, neurophysiological markers of the primary motor cortex (M1), including resting motor threshold (rMT), motor evoked potentials (MEPs), and silent period (SP), were assessed in both hands of a right-handed 10-year-old girl with a history of epilepsy and right hemispheric polymicrogyria. Bilateral MEPs with short latencies were elicited from the contralesional side. The average MEP amplitude and the latency for the patient's paretic and non-paretic hands differed significantly. We conclude that nTMS is a safe and tolerable procedure that can be used for presurgical evaluation in children with intractable epilepsy.