A Multicenter Retrospective Observational Cohort Study of Seizure Freedom before Lennox-Gastaut Syndrome (the "Gap"). Opportunities for Prevention.

Objective: Lennox-Gastaut Syndrome (LGS) is a severe, often treatment-resistant epilepsy syndrome typically diagnosed in early childhood. Many have seizures before diagnosis. Some have periods of seizure freedom before treatment resistance, i.e., a "gap." Review of these gaps may identify early candidate biomarkers of LGS and/or highlight opportunities for intervention.

Methods: We reviewed charts of children diagnosed with LGS born in 2008-2010 and diagnosed with LGS by 2014 at five academic medical centers in New York City using the RENYC (Rare Epilepsies in New York City) database. We collected dates of events of potential biomarkers by chart abstraction, including onset of slow spike-and-wave (SSW) and onset and offset of seizure freedom. Seizure-free periods ("gaps") were defined as greater than 30 days without unprovoked seizures.

Results: Thirty-three children had LGS (52% male; etiology 33% structural-acquired, 6% structural-congenital, 3% genetic-structural, 24% genetic, 33% unknown). Twenty-two (67%) had a gap before diagnosis. Eight of these twenty-two (36%) had SSW described before the gap, five (23%) during the gap, and six (27%) after the gap. A history of infantile epileptic spasms syndrome (IESS), age at seizure onset, and age of tonic seizure onset were not different between those with and without a gap. Of 20 (61%) with a history of IESS, 10 (30% of the full cohort) had not received recommended therapy (i.e., ACTH, prednisolone, or vigabatrin) as first-line treatment.

Conclusions: The appearance of SSW, even in seizure-free children, may herald the development of LGS in high-risk children. Further studies on its predictive value are warranted. Our findings also highlight use of recommended first-line therapy for infantile spasms as a potentially modifiable treatment gap in children who subsequently develop LGS.