Three adolescent patients with hemiconvulsive seizures and 3-cps generalized spike-and-wave discharges on EEG are reported from the National Hospital, Queen Square, London, UK. All are seizure-free following treatment with sodium valproate or/and lamotrigine, whereas prior treatment with carbamazepine was only partially effective. The diagnosis of idiopathic generalized epilepsy is supported by the EEG, normal CT or/and MRI, and pharmacological response. 
COMMENT. Idiopathic generalized epilepsy (IGE) is a heterogeneous syndrome. Asymmetrical cortical hyperexcitability is favored as the explanation for the hemiconvulsive seizures in the above small series. In the monozygous discordant twin study (Briellmann et al, 2001), IGE was associated with asymmetrical brain volume abnormalities on quantitative MRI, suggesting a subtle maldevelopment that might explain hemiconvulsive seizures in rare cases.