LAUSR

New-onset refractory status epilepticus (NORSE) is a severe neurologic emergency condition characterized by refractory status epilepticus (SE) without readily identifiable cause in otherwise healthy individuals.1 After the publication of our initial report on cryptogenic NORSE (C-NORSE),2 the term “NORSE” was defined by an international group of experts as a clinical presentation, not a specific diagnosis in 2018.3 When the cause remains unknown despite the extensive workup, it is called “C-NORSE.”3 NORSE can be caused by viral, paraneoplastic, or autoimmune etiologies, but half of the patients are cryptogenic.1 In clinical practice it is crucial to differentiate C-NORSE from secondary NORSE with neuronal autoantibodies at the early stage of SE; however, in an emergency condition it is often difficult to obtain autoantibody test results in appropriate time. Therefore, we previously developed a clinically based “C-NORSE score” (range, 0-6) based on the 6 clinical features to predict C-NORSE at the early stage of convulsive SE, in which the clinical features are obtained by history taking, neurologic assessment, and conventional tests that are accessible to most physicians (CSF, MRI, or EEG studies). We reported our preliminary results by comparing the clinical features of 11 adult patients with C-NORSE with those of 32 patients with anti-NMDA receptor (NMDAR) encephalitis.2 The C-NORSE score was higher in patients with C-NORSE than those with anti-NMDAR encephalitis.2 However, the scale score has not been validated yet. In the study reported by Yanagida et al,4 the sensitivity and specificity of a high-scale score (≥5) for predicting C-NORSE were 93.9% and 100%, respectively. We also added several comments when using the scale score (Table 1). This study shows that (1) patients with the high-scale score are more likely to be negative for neuronal surface antibodies, (2) C-NORSE score is a useful diagnostic tool at the early stage of convulsive SE of unclear etiology before autoantibody test results become available, and (3) patients with C-NORSE have distinctive clinical features.4 Patients with C-NORSE often present with high fever, followed by refractory SE (occasionally superrefractory SE). Early brain MRI may show symmetric medial temporal lobe abnormalities mimicking autoimmune limbic encephalitis (ALE); however, C-NORSE should be discriminated from ALE. Follow-up MRIs may help differentiation from autoimmune encephalitis. C-NORSE is a devastating epileptic syndrome of unknown causes, probably of diverse etiologies including autoimmunity, neuroinflammation, or individual susceptibility to seizure.4 Autoantibodies may not play an important role because unfixed immunohistochemistry did not show neuronal surface antibodies; TA B L E 1 C-NORSE score4