To determine seizure free intervals in newly diagnosed focal epilepsy patients prior to treatment intervention and assess patient specific definition of “seizure freedom.”  

The ILAE proposed “seizure freedom” as “freedom from all types of seizures for 12 months or three times the inter-seizure interval within the 12 months pre-intervention, whichever is longer,” using the “Rule of Three.”  The Human Epilepsy Project is a prospective, observational, multicenter study which enrolled patients with newly diagnosed focal epilepsy and followed them for a minimum of 3 years.  Data regarding seizure frequency was collected prior to intervention and allows for real life application of the ILAE suggested rule to assess outcomes.

421 participants were evaluated. The seizure frequency pretreatment and date of treatment initiation were collected.  Seizure clusters were considered a single event.  If a patient had three or fewer seizure events in the year prior to treatment and a longer inter-seizure interval within the two years prior to treatment, then this longer inter-seizure interval was used. The longest inter-seizure interval in the year pretreatment was calculated and multiplied by three.  If only one seizure event had occurred pretreatment, the inter-seizure interval was labelled indeterminate (IND). 

Of the 421 participants, the seizure free interval could be determined in 360. For 299 participants 1 year was longer than three times their previous seizure free interval.  For the remaining 61 participants the median seizure free interval was 180 days, mean 233 days, with a range of 122-649 days.  2 participants had intervals calculated using the two years prior to treatment which resulted in inter-seizure intervals of 365 and 601 days.

In this HEP cohort majority of patients could be considered seizure free following treatment at the one year mark by the ILAE definition, however a subset will require longer follow up to assess treatment response.