[Epileptic signs in alterations of neuronal migration]

A wide range of conditions are due to alterations in neurone migration (ANM). Mental retardation, motor disorders and epilepsy are seen in all these disorders. Anomalies included with the ANM are those produced at the time of neuronal migration in the phase prior to neurone proliferation and during the time following cortical organization. All these have a common characteristic, namely an anomalous cerebral cortex (cerebral dysplasias).

There is a high incidence of epilepsy in ANM (60%), appearing early (10% neonatal, 42% before 1 year old). The frequency of crises increases with age. Extended and diffused generalized forms presents as epileptic encephalopathies (Ohtahara, West, Lennox-Gastaut), whilst focal forms are seen as simple motor, partial crises, complex and secondarily generalized crises with a tendency to status epilepticus and also to continuous partial epilepsy. In diffuse, extensive forms, the EEG is characterized by large amplitude theta-delta rhythm activity (specific) with the presence of rapid activity (15-25 Hz) and of large amplitude (150-300 microV) which may also be found in other processes. In localized forms the recordings vary: localized discharges with/without crises, multifocal discharges in more than two lobes with a defined critical area, positive discharges, ipsilateral spike-and-wave complexes associated with focal discharges or with normal recordings. We review different types of ANM: in the phase of proliferation (hemimegalencephalia), the agyria-paquigyria complex; in phase of migration: type I lissencephalias (Miller-Dieker), layered heterotopias (double cortex), type II (cobblestone) lissencephalias and neuronal heterotopias, and in the phase of organization of the cortex: polymicrogyria and the esquissencephalias I and II.

The functional prognosis in ANM depends on the control of the crises rather than on the extent of the lesion. Surgical treatment leads to 42% good or excellent results.