The Seasonality of New-Onset Refractory Status Epilepticus (NORSE).

The 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 NORSE is a disorder of immunity, likely post-infectious. Consequently, seasonal occurrence might be anticipated. Here, we investigated if seasonality is a notable factor regarding NORSE presentation. We combined four different datasets with a total of 342 cases, all from the northern hemisphere, and 62% adults. The incidence of NORSE cases differed between seasons (p=0.0068) and was highest in summer (32.2%) (p=0.0022) and lowest in spring (19.0%, p=0.010). While both FIRES and non-FIRES cases occurred most commonly during the summer, there was a trend towards FIRES cases being more likely to occur in winter than non-FIRES cases (OR 1.62, p=0.071). The seasonality of NORSE cases differed according to the etiology (p=0.024). NORSE cases eventually associated with autoimmune/paraneoplastic encephalitis occurred most frequently in summer (p=0.032) and least frequently in winter (p=0.047), while there was no seasonality for cryptogenic cases. This study suggests that NORSE overall and NORSE related to autoimmune/paraneoplastic encephalitis are more common in summer, but that there is no definite seasonality in cryptogenic cases.