Focal cortical dysplasia type 1b as a cause of severe epilepsy with multiple independent spike foci.

To investigate the clinical picture, the neurophysiological pattern, and neuropathological features of a young woman with severe drug-resistant epilepsy of unknown cause. We used the patient's clinical records from the age of 2 to 20years including neurophysiological patterns recorded via both scalp and cortex electrodes and results of studies conducted on the brain neuropathological specimen. The patient, with severe mental/psychomotor retardation, suffered from severe epilepsy from an early age, characterized by daily seizures of multiple types (atypical absences, tonic, and complex partial seizures), high frequency, and intractability. The neurophysiological pattern indicated multiple independent spike foci (SE-MISF). When she was 16, a vagal nerve stimulator was implanted without success. Neither neuroimaging (brain MRI and ictal SPECT) nor surface EEGs identified unique loci of seizure onset, establishing her as a candidate for a complete callosotomy. When the patient was 19, before the callosotomy, invasive EEG (i.e., electrocorticography) using just a few electrodes in different lobes showed the presence of a distinctive pattern. The surgical specimen, taken very close to one of the activity sites, showed architectural abnormalities and neurons that were giant or immature but not dysmorphic, indicative of focal cortical dysplasia (FCD) type 1b. Twelve months after the callosotomy, according to the Engel score, the patient exhibited a large improvement in quality of life, without permanent complications from the interhemispheric disconnection. (1) Hidden FCD type 1b could represent a missing diagnosis in patients with SE-MISF in the absence of other causes for their seizures. (2) Complete callosotomy can be efficacious in patients with SE-MISF with hidden FCD type 1b.