NORSE is a condition characterized by refractory SE without readily identifiable cause in otherwise healthy individuals. When the cause remains unknown despite extensive work-up, it is called C-NORSE. To facilitate the prompt recognition of C-NORSE (e.g., before neuronal antibody test results are available) we recently developed a score (range, 0-6) based on 6 clinical features: 1) Refractoriness to anti-epileptic drugs, 2) previously healthy individual, 3) presence of prodromal high fever, 4) absence of prodromal behavioral or memory alterations, 5) absence of dyskinesias, and 6) symmetric brain MRI abnormalities (Neurol Neuroimmunol Neuroinflamm 2017;4[6]:e396). Each of these features represents 1 point, but the first 2 clinical features were mandatory, and a high score (≥5) at early disease stage predicted C-NORSE.

To validate a clinically-based score that predicts cryptogenic new-onset refractory status epilepticus (C-NORSE) at early stage of status epilepticus (SE).

The usefulness of the indicated scale score in predicting C-NORSE was assessed in 78 patients who presented with SE of unclear etiology (before neuronal antibody tests results were known).

Patients with a high score (≥5) (n=23, median age 25 years) had more frequent prodromal fever, mechanical ventilation support, and symmetric MRI abnormalities, and had less frequent dyskinesias, and absent prodromal psycho-behavioral symptoms, CSF oligoclonal bands, tumor association or neuronal antibodies than those with a low score (≤4) (n=55, median age 25 years). The 78 patients with SE were finally diagnosed with autoimmune encephalitis with neuronal antibodies (n=30, with NMDAR [n=28], GABAaR [n=1], or unknown [n=1]), C-NORSE (n=24), and other miscellaneous diseases (n=24). The sensitivity and specificity of a high score for predicting C-NORSE were 95.8% (23/24) and 100.0% (54/54), respectively.

Patients with a high score in the indicated scale are more likely to have C-NORSE, making it a useful diagnostic tool at early stage of SE before antibody test results become available.