Cortical dysgenesis: serial EEG findings in children and adults

Cortical dysgenesis (CD) is becoming increasingly recognised as a cause of epilepsy in otherwise cryptogenic cases. We describe the serial EEG findings in 22 patients with focal/localised CD. The EEGs covered a minimum period of 5 years in each case (median = 13 years, range: 5-30 years), beginning in childhood. Median age at seizure onset was 3 years (range: 3 weeks-10 years, n = 21). The EEG was normal in the one patient, a 6 year old, who did not have epilepsy. Background rhythms appropriate for age were preserved in the majority of patients (18/22). Slow activity localised to the area of CD was seen in 11 patients; in 3 patients, this did not appear until the second decade of life. Epileptiform discharges were seen in at least one EEG in 20 patients: these were continuous or near-continuous (6 patients) or occurred recurrently in short runs (6 patients). In 6 patients, these discharges appeared only after the second decade of life and in 11 patients, they became more widespread over time. In the remaining patients, the EEG changes did not evolve. Sleep failed to produce new abnormalities (n = 15). None of the patients showed EEG features characteristic of lissencephaly or evolution to the Lennox-Gastaut syndrome. Even in this selected cohort of patients who had undergone serial clinical EEGs, the EEG abnormalities in focal/localised CD appeared relatively stable and showed only moderate changes over time. CD must be included in the differential diagnosis of any patient who presents with localised slow activity on EEG.