Evaluation of the International League Against Epilepsy 1981, 1989, and 2017 classifications of seizure semiology and etiology in a population-based cohort of children and adults with epilepsy

Abstract

Objective: The International League Against Epilepsy (ILAE) has revised the classification of epilepsies and seizures on several occasions since the original classification published in 1964. It is unclear if these changes have impacted the characterization of epilepsy, including the clinical validity of seizure semiology or epilepsy outcomes in resource-poor areas. We aim to address this important knowledge gap.

Methods: We reviewed the clinical seizure semiology and etiological data of 483 persons with epilepsy identified from a population-based survey in rural Kenya. The seizure semiology and etiological data were classified using the 1981 (for seizures) and 1989 (for epilepsy) ILAE criteria and then reclassified according to the ILAE-2017 criteria. Logistic regression models adjusted for potential confounders were used to measure the associations between the seizure semiology and different clinical and electroencephalographic features of epilepsy.

Results: Focal (formerly localization-related) and generalized epilepsies were lower in ILAE-2017 (56% and 29%) than that of ILAE-1989 (61% and 34%), P < .001 and P < .001. Combined focal and generalized epilepsy type in ILAE-2017 accounted for 11% of epilepsies. Individual seizure types were statistically similar in both ILAE-1981 and 2017. New classification categories in ILAE-2017 such as unknown seizures and epilepsies were identified, and the proportions were similar to the unclassified category in ILAE-1989, 6% and 5%, respectively. The most common causes of epilepsy were symptomatic (76%) in the ILAE-1989 criteria, with infectious (45%) and structural (36%) causes were highest in the ILAE-2017 criteria.

Significance: Our study confirms that the two ILAE classification schemes are broadly consistent, but the introduction of the combined onset seizure category in ILAE-2017 significantly reduces the proportion of mutually exclusive focal and generalized seizures. The comprehensive classification of etiology categories in ILAE-2017 will facilitate appropriate treatment and improve prognosis.

Keywords: ILAE-1981; ILAE-1989; ILAE-2017; classification; epilepsy; outcomes; seizure.