Electroencephalographic change of non-affected side of hemimegalencephaly and developmental progress after hemispherotomy

Hemimegalencephaly is characterized by severe psychomotor impairment and intractable epilepsy, which is often requires a hemispherotomy. After hemispherotomy, epileptic discharges may sometimes occur in the non-affected hemisphere even when clinical seizures do not recur for a long time. We evaluated six cases of hemimegalencephaly after hemispherotomy with a seizure-free period lasting at least 36 months, which we could track using video-electroencephalography. Developmental age (DA) and developmental quotient (DQ) were evaluated using the developmental check-list (Kinder Infant Developmental Scale). We found the DQ declined and the total DA increased in all cases. To study the correlation between DA and epileptic discharges in the non-affected hemisphere, we measured the paroxysmal-index (PI) the number of one-second bins containing one or more epileptic discharges in the non-affected hemisphere, divided by the total number of seconds. The PI and DA data were collected at the same time during every regularly-scheduled evaluation. We calculated the rate of change of PI and DA. Interestingly, expressive language development and PI were negatively correlated when the PI increased at a rate above average. The receptive language DA and PI was not correlated. This finding suggests the expressive language development delay may worsen when epileptic discharges of non-affected side increase.