Febrile convulsions with focal sharp waves: A subgroup of benign partial epilepsies of childhood with multifactorial etiology

Studies on the prognosis of febrile convulsions (FC) have scarcely considered the heterogeneity of FC and its relationship to the risk and the variable nature of subsequent afebrile seizures. Meaningful study of this issue requires a sample of FC children that is as homogeneous as possible. One such FC subgroup is children with focal sharp waves (shw) in the electroencephalogram (EEG) of a type characteristic of benign partial epilepsies (5%–10% of all FC children). Because the incidence of FC is elevated in children with benign partial epilepsy, the question arises whether these entities have certain pathogenetic mechanisms in common. Because only children with long-term follow-up are suitable for a study of these problems, the results obtained here allow no quantitative inferences regarding prognosis. Inclusion criteria were: 1) FC as the first seizure symptom; 2) focal shw characteristic of benign partial epilepsy; 3) first EEG before the fifth year of life; 4) at least four EEGs between the second and the eighth year of life. One-hundred and twenty-eight children were ascertained. Duration of follow-up ranged from 1–33 years. A positive family history of seizures was found in 34% of probands. The incidence of neonatal seizures was remarkably elevated (6%). Prolonged FC and FC with focal symptoms were significantly overrepresented. Long lasting FC (>60 minutes) were associated with an occipital location of the shw. Fifty-nine children suffered subsequent afebrile seizures or epilepsy (selected material): idiophathic partial epilepsy (58%); idiopathic generalized epilepsy (12%); severe epilepsies (22%), usually with intractable complex partial seizures. The latter were clearly associated with FC lasting longer than 1 hour. In 91% of the patients generalized genetic EEG patterns like generalized spikes and waves, photoparoxysmal response, and theta rhythms were eventually detected. Among the shw findings, precentral (70%) and occipital (50%) foci predominated. Of 69 investigated siblings focal shw were detected in 14%. Febrile convulsions with focal shw represent a multifactorial disorder. The combined action of five factors seems relevant: 1) a hereditary impairment of brain maturation (represented by the shw-EEG trait); 2) a genetic anomaly expressed by photoparoxysmal response; 3) a genetic cortical hypersynchronization (theta rhythms); 4) the generalized spike wave abnormality; and 5) a genetic predisposition to FC that is represented by a high incidence of FC in relatives but is not expressed specifically in the EEG. Subsequent epilepsies are idiopathic (mostly partial) or the consequence of FC lasting more than 1 hour.