New onset refractory status epilepticus ( NORSE ) versus refractory status epilepticus not meeting NORSE criteria: A comparative clinical and electroencephalography‐based study

OBJECTIVE: New onset refractory status epilepticus (NORSE) is a rare, severe presentation of refractory status epilepticus (RSE), with approximately half of cases cryptogenic NORSE (c-NORSE). We compared electroencephalographic (EEG) findings alongside clinical features between NORSE and RSE not meeting NORSE criteria to better understand outcomes and prognostication. METHODS: This retrospective cohort study analyzed 81 RSE patients admitted to the intensive therapy unit (ITU) at the National Hospital for Neurology and Neurosurgery and University College London Hospital (2007-2023). Patients were categorized as RSE not meeting NORSE criteria (n = 52) or NORSE (n = 29). EEG features, treatment, and outcomes (ITU stay, mortality, cognitive outcome, and antiseizure medication [ASM] use), were evaluated. RESULTS: Of 29 NORSE patients (15 c-NORSE, 51.7%; 14 etiology-identified NORSE, 48.3%), autoimmune (20.7%) and infectious (17.2%) etiologies were most prevalent. Six-month mortality was higher in c-NORSE than etiology-identified NORSE (20.0% vs. 7.1%), but similar between NORSE and RSE not meeting NORSE criteria (13.8% vs. 21.1%). EEG analysis revealed longer seizure duration (mean = 243.38 vs. 51.67 s, p < .001), a tendency to higher seizure frequency (.013 vs. .009 seizures/min, p = .076), and increased presence of generalized periodic epileptiform discharges and stimulus-induced rhythmic, periodic, or ictal discharges in NORSE than RSE not meeting NORSE criteria. Across all patients, higher initial seizure burden correlated with longer ITU admissions and worse outcomes. Compared with RSE not meeting NORSE criteria, NORSE patients had longer ITU stays (median = 51 vs. 11 days, p < .001), more ASMs (mean = 3.91 vs. 2.00, p = .031), greater sedative use (mean = 2.17 vs. 1.00, p < .001), and more frequent cognitive impairment at discharge (88.9% vs. 62.2%, p = .037). SIGNIFICANCE: NORSE, particularly c-NORSE, tends to follow a more severe course than RSE not meeting NORSE criteria, with more severe background EEG features including the initial EEG, greater seizure burden, longer ITU stays, and increased incidence of cognitive impairment at discharge. Six-month mortality was similar, implying additional contributing factors to mortality.