Relationships within the idiopathic generalized epilepsies

The relationships between the various epileptic syndromes, which comprise the idiopathic generalized epilepsies that commence after infancy, were explored in 451 patients by comparing the incidences of various clinical and electroencephalographic features in subsets of the patients, determined primarily by their clinical patterns of seizure phenomena (absences, myoclonic and generalized tonic-clonic seizures), and secondarily by their ages at the onset of their seizures. The approach showed a bimodal distribution of ages of onset in the absence epilepsy group only. More subjects whose absences had begun under 10 years of age experienced very frequent episodes (52.0% vs 26.9%) and fewer experienced generalized tonic-clonic seizures (44.0% vs 71.2%). These differences were consistent with the distinction made in the International League Against Epilepsy's Classification between childhood and adolescent onset absence epilepsy. There were no unambiguous age of onset related differences in the incidences of the features studied within each of the myoclonic seizure and the generalized tonic-clonic seizure only groups, although there were differences in the incidences of the features between the two groups. Thus the idiopathic generalized epilepsies studied appeared to comprise a number of discrete entities rather than a smooth continuum of age of onset related epileptic phenomena.