A NEUROEPIDEMIOLOGICAL STUDY OF CHILDHOOD EPILEPSY IN OKAYAMA PREFECTURE, JAPAN, BY THE NEWLY PROPOSED ILAE CLASSIFICATION IN 2001

Objectives: To clarify problems in the application of the newly proposed classification of epilepsies (International League Against Epilepsy: ILAE, 2001) to epidemiological studies of epilepsy.

Methods: We performed an epidemiological study in Okayama Prefecture, Japan, in 1999. Among 250,997 children under 13 years of age, 2,220 epileptic patients were ascertained and were classified according to the current international classification (ILAE, 1989). In the present study, we reclassified them according to the newly proposed classification (ILAE, 2001), focusing on axes #2 (seizure types) and #3 (syndromes).

Results: We identified only 269 patients (12.1%) with specific epileptic syndromes out of the original 2,220 epileptic children, including 26 with newly defined syndromes. The remaining 1,761 patients, whose epilepsy had previously been classified as neocortical epilepsies without specific etiology or under major categories only (for example, symptomatic generalized epilepsy) according to the ILAE 1989 classification, were excluded from the new classification of epileptic syndromes. We applied axis #2 (seizure-type classification) to these 1,761 patients. In 102 of them (5.8%), at least one seizure type could not be classified because of the lack of proper positions in the new classification (for example, consciousness clouding only, autonomic symptoms only). Among all the 1,153 seizure types classified, secondarily generalized seizures (89.8%) and hemiclonic seizures (3.7%), which did not reflect specific anatomical substrate, were in the great majority.

Conclusion: Only a small number of patients were diagnosed as having specific epileptic syndromes in the general population. The new concept of epileptic seizure types, reflecting anatomical substrate, could not be properly applied to most cases, since they had no specific anatomical substrate.