Two types of febrile seizure: anoxic (syncopal) and epileptic mechanisms differentiated by oculocardiac reflex.

The duration of cardiac asystole induced by ocular compression was measured in 100 consecutive children referred for electroencephalographic examination after one or more febrile convulsions (FC). The children were classified into three groups-namely, those with anoxic FCs, those with epileptic FCs, and "others"-according to the appearances of the FC and the electroencephalogram (EEG). In 14 children the description of the FC suggested non-epileptic anoxic cerebral seizures such as are seen after prolonged syncope or breath-holding. In 35 children the FCs were assumed to be epileptic in mechanism on the basis of unilateral (hemiclonic) twitching, known cerebral disease, a family history of epilepsy, or spikes on the EEG. In the 51 "others" the FCs could not be classified. Definitely abnormal asystole (four seconds or over) was induced by ocular compression in half the anoxic group, in 16% of the "others," but in none of the epileptic group. The differences between the degree of asystole induced in each of the three groups was highly significant (P=0.005).These results support the hypothesis that vagal-mediated cerebral ischaemic anoxia is implicated in the genesis of FCs that resemble anoxic seizures and in a substantial number of those without an obvious epileptic mechanism. The significance, genetics, management, and prognosis of FCs must now be re-examined in this light.