Startle-induced epilepsy in a patient with epidermal nevus syndrome.

Startle-induced epilepsy was observed in a 5-year-old boy with epidermal nevus syndrome. He manifested linear nevus on the face and neck, mild mental retardation, and right hemiparesis. Massive myoclonus, followed by tonic seizures, had been triggered by unexpected auditory stimuli since 3 years of age. The startle-induced seizures were the only epileptic manifestation. Interictal EEG occasionally depicted spontaneous focal spikes and waves in the left frontotemporal area, and ictal EEG depicted vertex spikes and then diffuse slow spike-and-wave complex bursts. Left frontal and perisylvian cortical atrophy and a white matter abnormality in the left frontal area were revealed by magnetic resonance imaging. Single photon emission computed tomography demonstrated diffuse low perfusion in the left cerebral hemisphere. Lower amplitude potentials in the left cerebral cortex were evident during somatosensory evoked potential evaluation. These results indicate that hemispheric dysfunction could cause startle-induced epilepsy in this patient.