How long for epilepsy remission in the ILAE definition?

To the Editors: Revision of the operational definition of epilepsy has served in part as motivation to gather welcome new data on the time required for epilepsy to be considered in remission. In a recent study, Sillanp€a€a and colleagues followed 148 patients with childhood-onset epilepsy. For certain subgroups, the 5-year remission was as predictive as a 10year remission of a long-term remission. However, for other subgroups, the 10-year remission was more predictive of long-term remission. For example, as estimated from their Figure 3, both for all patients and for patients with generalized epilepsy, 5-year remissions with the last 2 years off antiseizure medicines were associated with subsequent relapses in about 15%, with the 95% confidence intervals (CIs) extending above 20%. In comparison, all patients and patients with generalized seizures who were 10-years’ seizure-free with the terminal 5 years off antiseizure medicines had a relapse rate <5% and an upper confidence limit of around 15%. The traditional epilepsy definition of two unprovoked seizures >24 h apart was modified to make it possible to “outgrow” epilepsy. What seizure-free period would designate a likely condition of no future seizures? The Task Force recognized that relapse rates for people with epilepsy probably always remain above baseline general population levels. For that reason, the Task Force avoided the word “cure.” We employed “resolved” as a descriptor, rather than “remission,” which some people associate with cancer. In the absence of solid data, the Task Force chose the conservative time-period of 10 years of seizure freedom and 5 years off antiseizure medicines. The study by Sillanp€a€a is one investigation with a relatively small sample size and subjects having limited etiologies of epilepsy, in that all had childhood-onset epilepsy. Relapse rates might vary considerably among different populations with varied epilepsy etiologies. Self-limited age-dependent syndromes and other special etiologic categories might merit separate consideration. For these reasons, the Task Force and the International League Against Epilepsy (ILAE) consider it premature to alter the published definition of epilepsy, but we can envision doing so in the future after further accumulation of broadly applicable data and larger cohort sizes from which to extrapolate findings. DISCLOSURE