Medically intractable generalized tonic-clonic or clonic seizures in infancy

Two clinical entities have been proposed for medically intractable generalized tonic-clonic or clonic seizures in infancy: severe myoclonic epilepsy in infancy (SME) and high voltage slow wave-grand mal syndrome (HVSW-GM). In this report, the author reevaluates both syndromes in addition to patients with variations of the syndrome. To investigate general characteristics and pathophysiological factors of such intractable seizures in infancy, the following criteria common to both SME and HVSW-GM were established: generalized tonic-clonic seizures with onset before the age of 1 year as the principal seizure type; epilepsy that is not classifiable as partial or generalized by all the clinical data including EEG findings; mental and motor dysfunction appearing after seizure onset; no epileptiform activities in the EEG in the initial stage; and therapeutic resistance at the commencement of therapy. Of 22 patients meeting all the criteria, 12 were diagnosed as having SME, six as having HVSW-GM, and four as having variations of the disorder. The percentage of cases having status epilepticus and an obtunded state in the SME group was high, with the other groups not showing such tendencies. The percentage of cases with severe mental dysfunction, abnormal brain computed tomography findings, and poor prognosis was lowest in the HVSW-GM group, intermediate in the variant group, and highest in the SME group. The variant appears to be an intermediate group between SME and HVSW-GM. It is suggested that the three clinical entities, SME, HVSW-GM, and variant, share certain characteristics and may in fact be conceptualized as representing portions of a continuum. In conclusion, it is proposed that there is a common pathyphysiological basis for all three clinical entities and with all three parts of the “infantile refractory grand mal syndrome.”