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  • Updated 06.21.2023
  • Released 06.21.2023
  • Expires For CME 06.21.2026

New-onset refractory status epilepticus (NORSE) and febrile infection-related epilepsy syndrome (FIRES)



New-onset refractory status epilepticus (NORSE) and febrile infection-related epilepsy syndrome (FIRES) are rare and devastating conditions. Consensus definitions now propose a unifying and standardized framework for NORSE and FIRES (26). According to these definitions, NORSE is a clinical presentation, not a specific diagnosis, with the occurrence of de novo refractory status epilepticus in a patient without active epilepsy and without a clear acute or active structural, toxic, or metabolic cause. Usually, this means that history, examination, and initial ancillary investigations performed within the first 48 hours do not provide sufficient clues to establish a causal diagnosis. FIRES is a subgroup of NORSE preceded by a febrile illness between 2 weeks and 24 hours prior to the onset of refractory status epilepticus, with or without fever at the onset of status epilepticus (26).

Historical note and terminology

Historically, the acronym NORSE has been used variably and without a clear definition to describe cases of refractory status epilepticus of unknown etiology (77; 09; 35). In children, the related condition of FIRES has been studied under many different names (58; 05; 40; 49; 60; 39; 70). As NORSE and FIRES share many similarities, they are now considered to belong to the same clinical entity, and both terms can be used for children and adults, although FIRES is mainly described in children (50; 39).

NORSE includes cases of unknown etiology (cryptogenic NORSE or c-NORSE) if no cause is found despite extensive investigations as well as cases with a known etiology when a diagnosis is ultimately reached through these investigations.

An etiology is identified in approximatively 30% of NORSE cases (18; 46; 42). The majority of adult cases with a known etiology are due to sporadic or paraneoplastic autoimmune encephalitis (18). In most case series of children with FIRES, the cause almost always remains unknown, but the lack of etiological diagnosis is likely an inclusion criterion for most studies, introducing a selection bias (49; 39; 07; 52; 70; 64). Recent findings have increased our understanding of cryptogenic cases, which support the hypothesis of a postinfectious autoinflammatory mechanism (68; 42).

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