NORSE & FIRES
New-onset refractory status epilepticus (NORSE) and febrile infection-related epilepsy syndrome (FIRES) represent devastating clinical presentations characterized by the abrupt onset of refractory status epilepticus in previously healthy individuals without a readily identifiable acute or structural cause. Despite aggressive treatment with multiple antiseizure medications and anesthetic agents, these conditions carry mortality rates of 16–22% and leave the majority of survivors with chronic drug-resistant epilepsy and significant cognitive disability. The identification of inflammatory and autoimmune mechanisms has opened therapeutic avenues beyond conventional ASMs, including immunotherapy, the ketogenic diet, and targeted cytokine blockade.
Bottom Line
- NORSE definition: New-onset refractory status epilepticus in a patient without active epilepsy or preexisting relevant neurologic disorder, without a clear acute structural, toxic, or metabolic cause; it is a clinical presentation, not a specific diagnosis
- FIRES definition: A subcategory of NORSE requiring a prior febrile infection starting between 2 weeks and 24 hours before onset of refractory SE, with or without fever at SE onset; applicable to all ages (not exclusively pediatric)
- Etiology: Cryptogenic in ~50% of cases; autoimmune/paraneoplastic in ~36%; innate proinflammatory cytokines (IL-6, IL-1β, TNF-α) are elevated in serum and CSF, suggesting a neuroinflammatory pathogenesis
- Clinical course: Typically progresses through febrile illness → acute phase with refractory/super-refractory SE → chronic phase with drug-resistant epilepsy in >90% of survivors
- Treatment: International consensus recommends immunotherapy within 72 hours; ketogenic diet and second-line immunotherapy within 7 days; anakinra (IL-1 receptor antagonist) and tocilizumab (anti-IL-6) have emerged as promising targeted therapies
- Outcomes: Mortality ~16–22%; only 4% achieve full neurologic recovery; most survivors have chronic epilepsy, cognitive impairment, and vocational disability
Definitions and Classification
NORSE: New-Onset Refractory Status Epilepticus
NORSE was formally defined by an international consensus in 2018 and refined in subsequent publications. It is defined as a clinical presentation, not a specific diagnosis, occurring in patients without active epilepsy or other preexisting relevant neurologic disorders, with new onset of refractory status epilepticus without a clear acute or active structural, toxic, or metabolic cause. The term applies at the time of presentation, before the results of extensive diagnostic testing are available. Once an etiology is identified (e.g., autoimmune encephalitis, paraneoplastic syndrome), the underlying diagnosis replaces NORSE as the primary label.
FIRES: Febrile Infection-Related Epilepsy Syndrome
FIRES is a subcategory of NORSE that requires a prior febrile infection starting between 2 weeks and 24 hours before the onset of refractory status epilepticus, with or without fever at the onset of SE. Originally described as a predominantly pediatric entity (ages 2–17 years), FIRES is now recognized as applicable to all age groups. The preceding infection is typically nonspecific (upper respiratory or gastrointestinal) and resolves or is resolving before SE onset, distinguishing it from acute infectious encephalitis.
| Feature | NORSE | FIRES |
|---|---|---|
| Definition | New-onset refractory SE without clear acute cause in previously healthy individuals | NORSE subtype with preceding febrile illness (2 weeks to 24 hours before SE onset) |
| Age | All ages; median ~30 years in adults | All ages; classically school-age children (4–11 years); median ~8 years |
| Prodrome | May or may not have preceding illness | Febrile infection required by definition |
| Prevalence among RSE | ~10–16% of refractory SE cases; uncommon | Subset of NORSE; represents most pediatric NORSE cases |
| Etiology | Cryptogenic ~50%; autoimmune ~36%; infectious, paraneoplastic, or other in remainder | Predominantly cryptogenic; suspected postinfectious immune-mediated mechanism |
| Relationship | Umbrella term that includes FIRES | Subcategory of NORSE |
Relationship to Status Epilepticus Stages
NORSE and FIRES typically progress through the standard stages of status epilepticus:
- Developing SE: Initial seizures, often focal with secondary generalization
- Established SE: Seizures lasting >5 minutes, failing to respond to first-line benzodiazepines
- Refractory SE: Failure of two appropriately dosed ASMs in different classes — this is the defining stage for NORSE
- Super-refractory SE: SE persisting ≥24 hours despite continuous IV anesthetic infusions (midazolam, propofol, pentobarbital) — occurs in the vast majority of NORSE/FIRES patients; in one study, 26 of 27 adult NORSE patients progressed to super-refractory SE
Epidemiology and Etiology
Incidence and Demographics
NORSE is an uncommon presentation. In a Pediatric Status Epilepticus Research Group study, only 16% of children with refractory SE had NORSE. In adults with refractory SE, only 10.7% met NORSE criteria. There is no consistent sex predilection, though some series report a slight male predominance in adults.
Etiologic Categories
A 2023 systematic review and meta-analysis of adults with NORSE determined the following etiologic distribution:
- Cryptogenic (no identified cause): ~50% of cases — extensive workup fails to reveal an etiology; these are the true "cryptogenic NORSE" cases
- Autoimmune/paraneoplastic: ~36% — includes NMDA-R, LGI1, GABA-A, GABA-B, CASPR2, ANNA-1 (Hu) antibodies; these patients may be reclassified once an antibody is identified
- Infectious: ~5–10% — viral encephalitis (HSV, HHV-6), tuberculosis
- Other: Rare genetic causes, mitochondrial disease
Pathophysiology: The Cytokine Storm Hypothesis
The pathogenesis of NORSE/FIRES, particularly cryptogenic cases, is hypothesized to involve an aberrant innate immune response triggered by a preceding infection or other immune stimulus:
Neuroinflammatory Cascade in NORSE/FIRES
- A multicenter study comparing NORSE/FIRES patients with other refractory SE etiologies and healthy controls demonstrated significant elevation of three innate proinflammatory cytokines and chemokines in serum
- Key cytokines implicated: IL-1β, IL-6, and TNF-α are elevated in both serum and CSF; IL-6 levels correlate with SE severity and may serve as a therapeutic target
- Brain MRI studies demonstrate significantly higher blood-brain barrier permeability in NORSE patients compared with encephalitis patients without SE and healthy controls
- CSF often shows nonspecific lymphocytic pleocytosis and mildly elevated protein, supporting but not proving an inflammatory mechanism
- The cytokine hypothesis provides the rationale for targeted anti-cytokine therapies (anakinra for IL-1; tocilizumab for IL-6)
Clinical Course
Three Phases of NORSE/FIRES
| Phase | Duration | Clinical Features |
|---|---|---|
| Prodromal phase | Hours to 2 weeks before SE | Nonspecific febrile illness (FIRES), behavioral changes, headache, malaise; neurologic examination typically normal; EEG and MRI usually normal at this stage |
| Acute phase | Days to weeks (median 2–4 weeks; range up to months) | Onset of seizures → rapid escalation to refractory/super-refractory SE; often requires ICU admission and continuous IV anesthetic infusions; seizures frequently recur upon weaning of anesthetics (“wean-to-seize” pattern); multiorgan complications common |
| Chronic phase | Months to lifelong | Drug-resistant epilepsy in >90%; cognitive impairment (memory, executive function, processing speed); behavioral and psychiatric comorbidities; functional disability requiring rehabilitation |
Seizure Characteristics
Seizures in NORSE/FIRES typically begin as focal seizures (often temporal or perisylvian) that rapidly become bilateral. EEG commonly shows multifocal ictal onsets, sometimes migrating from one hemisphere to the other. A distinctive EEG pattern described in FIRES is the "waxing and waning" of ictal-interictal patterns, sometimes referred to as "quasi-periodic" discharges. The ictal-interictal continuum makes determination of individual seizure onset and offset challenging.
Red Flags: When to Suspect NORSE/FIRES
- Previously healthy child or young adult with new-onset refractory SE, especially following a febrile illness
- SE that fails to respond to first- and second-line ASMs despite adequate dosing
- "Wean-to-seize" pattern: seizures recurring every time anesthetic infusions are weaned
- Multifocal or migrating seizure onsets on EEG
- MRI initially normal or showing nonspecific findings; may develop bilateral temporal or multifocal cortical signal changes in the acute phase
- CSF with mild pleocytosis and elevated protein, but negative infectious workup
- Standard autoimmune encephalitis panel negative (cryptogenic NORSE) — does not rule out an immune-mediated process
Diagnostic Evaluation
Mandatory Workup
Because NORSE is defined by exclusion, a comprehensive evaluation is required to rule out identifiable causes of refractory SE:
| Category | Tests | Rationale |
|---|---|---|
| CSF analysis | Cell count, protein, glucose, oligoclonal bands, IgG index, cytology; HSV/VZV/enterovirus PCR; autoimmune encephalitis panel (serum + CSF); cultures | Essential to exclude infectious encephalitis and identify autoimmune antibodies; HSV encephalitis is the most important treatable mimic |
| Serum studies | Comprehensive metabolic panel, liver/renal function, ammonia, lactate, toxicology screen; autoimmune encephalitis panel; thyroid antibodies; ANA, ESR, CRP | Exclude toxic-metabolic causes; identify systemic autoimmune disease |
| Neuroimaging | Brain MRI with gadolinium (epilepsy protocol); repeat at 48–72 hours if initially normal | May be normal initially; may develop T2/FLAIR hyperintensity in mesial temporal structures, insular cortex, or diffuse cortical regions; DWI restriction may indicate cytotoxic edema from prolonged seizures |
| EEG | Continuous video-EEG monitoring (mandatory) | Required for seizure detection, treatment titration, and monitoring for subclinical seizures; multifocal ictal onsets support NORSE/FIRES |
| Cancer screening | CT chest/abdomen/pelvis; PET-CT; pelvic ultrasound/MRI; testicular ultrasound | Paraneoplastic causes account for a subset of NORSE; screening should be repeated at 6–12 months if initial evaluation is negative |
| Cytokine profiling | Serum and CSF IL-6, IL-1β, TNF-α (where available) | Elevated levels support inflammatory pathogenesis and may guide targeted cytokine-directed therapy (tocilizumab, anakinra) |
| Brain biopsy | Reserved for diagnostically uncertain cases refractory to all therapies | May reveal lymphocytic inflammation, gliosis, or other pathology; risk-benefit must be carefully considered |
Treatment
International Consensus Recommendations (2022)
In 2022, an international consensus group published 85 recommendations for the diagnosis and treatment of NORSE and FIRES in all age groups. The key treatment principles are:
- Standard ASM management for status epilepticus should follow established guidelines (benzodiazepines → second-line ASMs → anesthetic infusions)
- Immunotherapy should be considered for initiation within 72 hours of onset
- Second-line immunotherapy and the ketogenic diet should be considered within 7 days of onset in cryptogenic cases
- A median of 5 ASMs are typically used during the acute phase
- Withdrawal of anesthetic infusions should be gradual, with continuous EEG monitoring
Acute Management Algorithm
| Timeline | Intervention | Details |
|---|---|---|
| 0–60 minutes | Standard SE protocol | IV lorazepam 4 mg or IM midazolam 10 mg (first phase); fosphenytoin 20 mg PE/kg, valproic acid 40 mg/kg, or levetiracetam 60 mg/kg (second phase) |
| 1–24 hours | Refractory SE management | Continuous IV anesthetic infusion (midazolam, propofol, or pentobarbital); continuous EEG monitoring; ICU admission; intubation and mechanical ventilation as needed |
| Within 72 hours | First-line immunotherapy | IV methylprednisolone 20–30 mg/kg/day (max 1 g) for 3–5 days; IVIg 0.4 g/kg/day ×5 days may be given as alternative or in combination; PLEX if available |
| Within 7 days | Second-line immunotherapy + ketogenic diet | Rituximab 375 mg/m2 weekly ×4; if antibody identified, rituximab is recommended as first second-line agent; initiate ketogenic diet (4:1 ratio enterally; requires metabolic monitoring) |
| 7–14 days | Targeted anti-cytokine therapy | Anakinra (IL-1RA): 1–10 mg/kg/day SC (typically 100 mg twice daily in adults); tocilizumab: 8–12 mg/kg IV (max 800 mg) every 2–4 weeks; consider if refractory to above measures |
| Ongoing | Slow anesthetic wean + adjunctive therapies | Wean anesthetics over days to weeks with continuous EEG; consider additional ASMs (lacosamide, clobazam, perampanel, phenobarbital); address ICU complications (infections, thrombosis, critical illness myopathy) |
Immunotherapy in Detail
First-Line Immunotherapy
- IV methylprednisolone: 20–30 mg/kg/day (maximum 1 g) for 3–5 days; most commonly used first-line agent; may be followed by oral prednisone 1 mg/kg/day taper; corticosteroids are often the first immunotherapy administered
- IVIg: 0.4–2 g/kg divided over 3–5 days; may be given as an alternative to or in combination with corticosteroids
- Plasma exchange (PLEX): 5–7 exchanges on alternate days; logistically challenging in the ICU setting but provides rapid antibody removal
Second-Line Immunotherapy
- Rituximab: 375 mg/m2 weekly ×4; recommended if a pathogenic antibody is identified or highly suspected; B-cell depletion may reduce antibody production
- Cyclophosphamide: 750 mg/m2 IV monthly; reserved for severe cases refractory to rituximab; significant toxicity profile
Targeted Anti-Cytokine Therapies
Anakinra and Tocilizumab in NORSE/FIRES
- Anakinra (IL-1 receptor antagonist): Recombinant IL-1RA that blocks IL-1β signaling; administered subcutaneously at 1–10 mg/kg/day (typically 100 mg SC twice daily in adults); crosses the blood-brain barrier poorly but may be effective through peripheral immune modulation; case series report SE cessation in 50–60% of FIRES patients treated with anakinra; considered the most promising targeted therapy for FIRES specifically
- Tocilizumab (anti-IL-6): Humanized monoclonal antibody against IL-6 receptor; dosed at 8–12 mg/kg IV (max 800 mg) every 2–4 weeks; case reports and small series show SE termination after 1–2 doses with a median interval of 3 days from initiation; effective in some cases refractory to anakinra; rationale based on elevated IL-6 in NORSE/FIRES CSF
- Sequencing: The international consensus does not specify a preferred order; some centers use anakinra first (easier administration, rapid onset) and add tocilizumab if refractory; others begin with tocilizumab if CSF IL-6 levels are markedly elevated
- Duration: No consensus; typically continued for 1–3 months during the acute phase, then tapered based on clinical response
Ketogenic Diet
The ketogenic diet has emerged as an important adjunctive therapy in NORSE/FIRES, particularly in the pediatric population:
- High-fat, low-carbohydrate diet (typically 4:1 or 3:1 fat-to-carbohydrate+protein ratio) administered enterally via nasogastric or gastrostomy tube in the acute setting
- Mechanism: ketone bodies have direct anticonvulsant and anti-inflammatory effects; reduce neuronal excitability; modulate neurotransmitter release
- International consensus recommends initiation within 7 days of SE onset in cryptogenic NORSE/FIRES
- Case series report efficacy in 30–60% of FIRES patients, with seizure cessation or significant reduction within 1–2 weeks of achieving ketosis
- Early initiation (within the first 2 weeks) reported as a determinant of good outcome
- Requires monitoring for metabolic complications: metabolic acidosis, hypoglycemia, dyslipidemia, kidney stones, growth impairment in children
- May need to be maintained for months to years in the chronic phase; some patients remain on a modified ketogenic diet long-term
Other Adjunctive Therapies
- Ketamine: NMDA receptor antagonist; continuous IV infusion 1–5 mg/kg/hour; efficacy reported in three-fourths of pediatric refractory SE cases in a university hospital study; may have neuroprotective properties by blocking excitotoxic NMDA receptor activation
- Cannabidiol (epidiolex): Anecdotal reports in refractory FIRES; insufficient evidence for routine recommendation
- Hypothermia: Targeted temperature management (32–35°C) has been used in super-refractory SE; may reduce cerebral metabolic demand and neuroinflammation; limited evidence specific to NORSE
- Electroconvulsive therapy (ECT): Case reports of benefit in super-refractory SE; mechanism unclear; increases seizure threshold
- Vagus nerve stimulation: May be considered in the chronic phase for drug-resistant epilepsy following NORSE/FIRES
Treatment Pitfalls in NORSE/FIRES
- Delayed immunotherapy: Failure to initiate immunotherapy within 72 hours is associated with worse outcomes; do not wait for antibody results in the setting of refractory SE with high clinical suspicion for NORSE
- Premature anesthetic withdrawal: Too-rapid weaning of continuous infusions causes SE recurrence ("wean-to-seize"); slow, stepwise weaning over days to weeks with continuous EEG monitoring is essential
- Underuse of the ketogenic diet: Often initiated too late; should be considered within 7 days of SE onset per international consensus
- ICU complications: Prolonged ICU stays lead to ventilator-associated pneumonia, central line infections, VTE, critical illness myopathy/neuropathy, pressure injuries — vigilant preventive care is essential
- Propofol infusion syndrome: Avoid prolonged propofol use in children and use cautiously in adults; characterized by metabolic acidosis, rhabdomyolysis, cardiac failure, and renal failure
- Diagnostic tunnel vision: Continue to search for treatable etiologies (especially autoimmune and paraneoplastic) even after the acute phase; repeat antibody panels and cancer screening at 3–6 months
Outcomes and Prognosis
Mortality
Mortality rates in NORSE range from 16% to 22% in systematic reviews. A 2024 study of well-characterized NORSE cases reported a 19% mortality rate. Factors predictive of mortality include older age, presence of an acute etiology, progression to super-refractory SE, and prolonged duration of SE.
Long-Term Neurological Outcomes
| Outcome Domain | Frequency | Details |
|---|---|---|
| Chronic epilepsy | >90% of survivors | Drug-resistant in the majority; typically multifocal; may improve gradually over years but rarely achieves seizure freedom |
| Cognitive impairment | >80% of survivors | Memory deficits (hippocampal damage), executive dysfunction, reduced processing speed; severity correlates with SE duration |
| Psychiatric comorbidities | ~50–70% | Depression, anxiety, PTSD, behavioral changes; may develop months after the acute phase |
| Vocational disability | High | Many patients (adults) unable to return to previous employment or education; children often require special education services |
| Full neurologic recovery | ~4% | Only a small minority achieve complete neurologic recovery (2024 study) |
Predictors of Outcome
- Better outcomes: Younger age, shorter SE duration, identified autoimmune etiology (treatable), early immunotherapy initiation, early ketogenic diet initiation, lower Status Epilepticus Severity Score
- Worse outcomes: Older age, prolonged super-refractory SE, cryptogenic etiology, delayed treatment, need for multiple anesthetic agents, development of hippocampal atrophy on MRI
Emerging Therapies and Ongoing Research
Clinical Trials
The rarity of NORSE/FIRES has made randomized controlled trials extremely challenging. No RCTs have been completed to date. Current evidence is derived from case reports, case series, retrospective studies, and international consensus guidelines. Active areas of investigation include:
- Prospective registries: International NORSE/FIRES registries are collecting systematic data on demographics, treatments, and outcomes to guide future trials
- Biomarker-guided therapy: CSF cytokine profiling (IL-6, IL-1β) may identify patients most likely to respond to specific anti-cytokine agents, enabling precision immunotherapy
- JAK inhibitors: Baricitinib and tofacitinib are being explored for their broad anti-inflammatory effects in refractory autoimmune encephalitis; may have a role in NORSE
- Intrathecal immunotherapy: Direct CSF delivery of dexamethasone or rituximab has been used in isolated cases of super-refractory NORSE; may bypass blood-brain barrier limitations
- Gene therapy and antisense oligonucleotides: Preclinical research targeting inflammatory pathways in SE; not yet in clinical application for NORSE
Key Takeaways for the Clinician
- NORSE/FIRES should be in the differential diagnosis for any new-onset refractory SE without clear cause, particularly after a preceding febrile illness
- The approach must be multimodal: ASMs to suppress seizures + immunotherapy to address the underlying inflammation + metabolic therapy (ketogenic diet) + supportive ICU care
- Initiate immunotherapy within 72 hours; consider ketogenic diet within 7 days; add anakinra or tocilizumab if refractory
- Expect a prolonged ICU course (weeks to months); communicate realistic expectations to families early
- Long-term follow-up is essential: most survivors will require ongoing ASMs, cognitive rehabilitation, psychological support, and educational/vocational accommodations
- Participate in international registries and consensus efforts to improve evidence for this devastating condition
References
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- Gaspard N, Bhatt A, Bhatt RR, et al. New-onset refractory status epilepticus (NORSE) and febrile infection-related epilepsy syndrome (FIRES): state of the art and perspectives. Epilepsia 2018;59(4):745–752.
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