Definition and Diagnostic Criteria of NORSE
- NORSE is a clinical presentation of refractory status epilepticus (RSE) in individuals without prior epilepsy or relevant neurological disorders.
- Defined by ongoing SE unresponsive to benzodiazepines and at least one antiseizure medication, with no acute structural, toxic, or metabolic cause.
- FIRES (Febrile Infection-Related Epilepsy Syndrome) is a subcategory of NORSE, preceded by a febrile illness 24 hours to 2 weeks before SE onset.
- Diagnosis requires exclusion of known causes (e.g., stroke, infection, intoxication, metabolic derangements).
- Cases are termed "cryptogenic NORSE" if no cause is found, or specified if a cause (e.g., autoimmune encephalitis) is later identified.
Epidemiology and Clinical Presentation in Children
- Extremely rare: FIRES affects ~1 in a million children.
- Typically affects school-aged children and young adults; median pediatric age ~8–12 years.
- Prodromal febrile illness is common in ~2/3 of cases, often benign and without identified pathogen.
- Seizures are typically prolonged, convulsive, and refractory from onset, requiring ICU-level care.
- Encephalopathy, high seizure burden (dozens/hundreds per day), and lack of initial focal deficits are characteristic.
Pathophysiology and Proposed Mechanisms
- Presumed immune-mediated or post-infectious neuroinflammatory process, often without a confirmed antibody.
- Elevated cytokines (e.g., IL-6, IL-8, TNF-α) suggest innate immune activation in CSF and serum.
- Autoimmune encephalitis (e.g., anti-NMDA) is identified in a minority of cases; cryptogenic etiology is more common in children.
- Genetic or metabolic disorders (e.g., mitochondrial disease) rarely found in pediatric NORSE.
Diagnostic Approach
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