Classification of the epilepsies.

We review the development of the classification of the epilepsies. Primary epilepsies are relatively benign, usually age-limited syndromes without clinical or radiologic evidence of brain lesions, and are related to a heritable constitutional predisposition to epilepsy. They usually respond well to antiepileptic drugs. The biochemical correlates of primary generalized epilepsy have been demonstrated in animals and man and have been related to diffuse cortical hyperexcitability, which has been linked to this disorder. The pathophysiology of the primary partial or focal epilepsies is poorly understood but does not appear to depend on focal brain lesions. We suggest that these are due to relatively localized areas of cortical hyperexcitability confined to isolated corticothalamic sectors and depend on interrelations between a constitutional cortical hyperexcitability and normal cortical maturation. The secondary epilepsies are associated with clinical and radiologic evidence of brain lesions and are often resistant to anticonvulsants. Secondary generalized epilepsies, with an associated diffuse encephalopathy, are typified by the Lennox-Gastaut syndrome. The presentation of the secondary partial epilepsies depends on the site of the lesion. The pathogenesis of epilepsy is multifactorial, and a preexisting constitutional predisposition can interact with an acquired diffuse or focal encephalopathy, facilitating the clinical expression of one or the other.