The seasonality of new‐onset refractory status epilepticus (NORSE)

Abstract

AbstractThe etiology of new‐onset refractory status epilepticus (NORSE), including its subtype with prior fever known as FIRES (febrile infection‐related epilepsy syndrome), remains uncertain. Several arguments suggest that NORSE is a disorder of immunity, likely post‐infectious. Consequently, seasonal occurrence might be anticipated. Herein we investigated if seasonality is a notable factor regarding NORSE presentation. We combined four different data sets with a total of 342 cases, all from the northern hemisphere, and 62% adults. The incidence of NORSE cases differed between seasons (p = .0068) and was highest in the summer (32.2%) (p = .0022) and lowest in the spring (19.0%, p = .010). Although both FIRES and non‐FIRES cases occurred most commonly during the summer, there was a trend toward FIRES cases being more likely to occur in the winter than non‐FIRES cases (OR 1.62, p = .071). The seasonality of NORSE cases differed according to the etiology (p = .024). NORSE cases eventually associated with autoimmune/paraneoplastic encephalitis occurred most frequently in the summer (p = .032) and least frequently in the winter (p = .047), whereas there was no seasonality for cryptogenic cases. This study suggests that NORSE overall and NORSE related to autoimmune/paraneoplastic encephalitis are more common in the summer, but that there is no definite seasonality in cryptogenic cases.