Myoclonic epilepsies of infancy and childhood.

This chapter has reviewed the multiple types of childhood epilepsies customarily referred to as "myoclonic epilepsies" and has made an attempt at classification. A distinction was made on a clinical neurophysiological basis between true myoclonic and pseudomyoclonic seizures that include brief tonic and atonic attacks. The epilepsies characterized mainly by pseudomyoclonic seizures include infantile spasms (West's syndrome) and the Lennox-Gastaut syndrome. The epilepsies manifested principally by true myoclonic seizures comprise two subgroups: a symptomatic type, in which myoclonias are the result of fixed diffuse brain damage; and several cryptogenic forms. The latter may be divided, according to age of onset and clinical features, into several myoclonic syndromes: cryptogenic myoclonic epilepsy of infancy and early childhood, myoclonic epilepsy of childhood with absences, and myoclonic epilepsy of adolescence. Many intermediate and atypical forms exist; thus the proposed classification is only tentative.