An Electroclinical Study of Epilepsy Associated with Hemimegalencephaly and Focal Cortical Dysplasia with Bulging Lesions

Abstract

Purpose: It is well known that hemimegalencephaly (HM) is often associated with refractory early‐onset epilepsy and some characteristic EEG features. In addition to the typical HM cases, in which the entire hemisphere shows hypertrophy, there are some mild cases of HM with more localized lesions. On the other hand, a type of focal cortical dysplasia shows relatively large lesions with an accompanying increase in the thickness and volume of the abnormal cortex. The underlying white matter is often thin and abnormal, with an increased between the extent of the lesions and their electroclinical characteristics. Methods: We investigated the electroclinical and magnetic resonance imaging (MRI) characteristics of two patients with typical HM (group 1), one patient with mild HM (group 2), and two patients with the previously mentioned focal cortical dysplasis (group 3). Results: On MRIs, there was generalized hypertrophy of the entire hemisphere in both patients in group 1. There were lesions in the occipital lobe and a part of the temporal lobe in the one patient in group 2 and in the frontal lobe in both patients in group 3. The age at onset of seizures was 3 days after birth and 1 month in the patients in group 1. The onset of seizures was within 24 h after birth in the aforementioned patients of groups 2 and 3, and 7 days after birth in the afore mentioned patients of groups 2 and 3, and 7 days after birth in the remaining group 3 patient. As for epileptic syndromes, one patient in group 1 and one in group 3 showed the electroclinical findings of Ohtahara syndrome. One of them subsequently evolved into West syndrome. Another patient in group 3 showed the symptoms of West syndrome; however, it was not preceded by Ohtahara syndrome. The patient of group 2 showed localization‐related epilepsy throughout the clinical course. Regarding the type of epileptic seizures, the patient in group 2 had only partial seizures. The other four patients had both partial and generalized seizures, such as tonic spasms and myoclonic seizures. The interictal EEGs showed asymmetric barst‐suppression (Paladin, 1989) in all patients except for one in group 1. Alpha‐like activity (Paladin, 1989) was observed in all patients except for one in group 3. The triphasic complex (Paladin, 1989) was observed in every patient in all of the groups. At the end of the follow‐up period, all patients continued to have seizures and had severe mental retardation. Both patients in group 1 were able to walk on their own despite the hemiplegia. The patient in group 2 was a severely handicapped child with a double hemiplegia. Both patients in group 3 showed slight hemiplegias. One of them could walk on his own, and the other was severely handicapped. Conclusions: There was no relation between the type of epilepsy and the volume of the lesions. EEG findings characteristic of HM were observed in the patients in all three groups irrespective of the nature, the volume, and the location of the lesions. The patients in groups 1 and 3 showed early‐onset refractory epilepsies such as Ohtahara and West syndromes. All of them had both generalized and partial seizures. The patients in group 3 showed the same characteristic EEG findings as those in group 1. Therefore it is considered that both groups share a similar mechanism for the occurrence of their epilepsies.