Hemispheric epilepsy.

Abstract

This report documents clinical and EEG features of 13 patients whose most frequent EEG abnormality was unilateral interictal spike-waves that occurred consistently over the same hemisphere on multiple recordings. These 13 patients were selected from a 25000-patient database encompassing 25 years. The hemisphere involved was the left in 8 (62%) of the 13 patients. Bisynchronous spike-waves also appeared on a majority of recordings in 10 (77%) patients. Focal spikes occurred in a majority of recordings in 7 (54%) patients; these usually predominated in the frontal or frontal temporal regions and were always ipsilateral to hemispheric spike-waves. Their field distribution often merged with regional or hemispheric spike-waves. EEG evidence of ictal origin ipsilateral to hemispheric spike-waves appeared in 7 of 8 patients whose seizures were recorded; ictal potentials never predominated contralaterally. All patients had seizure disorders beginning in childhood or adolescence. Eleven (85%) had more than one type of seizure. Principal ictal types contained no focal phenomena in 10 (77%) patients. Bilateral motor seizures were tonic-clonic (12 patients), myoclonic (3), tonic (3) and atonic (1). Absence-like attacks occurred in 10 patients: only staring, automatisms and loss of awareness occurred in 6, with aurae in 3, and with motor phenomena in 3. Features of some seizures in 9 patients (69%) suggested a focal or unilateral origin or involvement, but these consistently occurred contralaterally to principal spike-waves in only 4 patients. At a median follow-up of 19 years, 11 patients (85 %) continued to have seizures; the 2 seizure-free patients required two anti-epileptic drugs each. History, neurological examination and neuro-imaging failed to disclose an aetiology or structural lesion in any patient. Eleven patients (85%) had normal intelligence. This newly documented syndrome of hemispheric epilepsy therefore comprises four components: (i) diffuse unilateral spike-waves on EEG which consistently appear over the same hemisphere in a given patient; (ii) a persistent, usually intractable seizure disorder with generalized ictal features in all patients and focal in most; (iii) onset of seizures in childhood or adolescence; and (iv) no apparent aetiology or related structural abnormality of the CNS.