MYOCLONUS ASSOCIATED WITH GENERALIZED EPILEPSY IN CHILDHOOD

Objectives: To clarify the pathophysiologies of myoclonus (MC) in generalized epilepsy (GE) in childhood.

Methods: Subjects were fourteen patients (M/F 7/7 aged 8–30y) with onset in childhood, including 5 Lennox-Gastaut syndrome (LG), 4 progressive myoclonus epilepsy (PME), 1 benign familial myoclonic epilepsy (BFME), 1 epilepsy with myoclonic absence (EMA), 1 SMEI, 2 other symptomatic GE (SGE). Polygrams, back-averaging (BA), SEP and cortical(C)-reflex were examined.

Results: 1) Except EMA, all showed distal dominant MC both in ictal and interictal stages. 2) Polygram showed frontal spikes and fronto-central dominant spike & wave complexes in all. Atonia of the mentalis tonus in NREM was observed except in EMA and BFME. 3) BA and SEP revealed 4 types of MC; Type A (PME, BFME): MC, duration <40 msec, preceded by premyoclonic potentials (<20msec) in the contralateral frontocentral areas, Type B (LG, SGE): Massive MC, duration>50msec, preceded by bilateral premyoclonic potentials (>39msec) predominantly over frontocental areas. Muscle innervations of MC showed a rostrocaudal lag in the brainstem. Type C (MAE): Rhythmic MC, duration 60msec, predominantly in the upper extremities following 3Hz diffuse spike & wave complexes, preceded by the frontal discharge. BA showed premyoclonic potentials preceding MC by around 76msec. Type D (LG, PME, SMEI, SGE): Distal dominant MC without premyoclonic potential. Giant SEP with C-reflex was recorded only in type A.

Conclusion: MC in type A is shown as cortical reflex MC and as subcortical MC in other 3 groups. Involvement of the rostral brainstem reticular formation is suggested in type B and that of the thalamocorticoreticular loop is suggested in type C. Despite no correlation with cortical event, hyperexcitability of the cerebral cortex, especially the frontal lobe could relate to subcortical MC in type D.