The mirror focus phenomenon and secondary epileptogenesis in human epilepsy

Although the mirror focus and secondary epileptogenesis are described in animal models of focal epilepsy, the relevance of these phenomena to human epilepsy is controversial. We reviewed 30 patients with unilateral epilepto genic low-grade structural lesions and sought evidence of secondary epilep togenesis. Patients with evidence of mirror foci were compared with patients with unilateral discharges. The incidence of interictal mirror foci was 27% Location of the primary epileptogenic lesion, duration of epilepsy, age of onset of epilepsy, and postoperative seizure outcome were not affected by the pres ence of a mirror focus. One patient had evidence of independent secondary epileptogenesis and had had seizures arising independently from that focus of homotopic cortex contralateral to a tumor 3.75 years after excision of the pri mary lesion. We conclude that secondary epileptogenesis is not uncommon in humans and that independent foci capable of generating seizures may be formed