Efgartigimod in Acute Neuromyelitis Optica Spectrum Disorders

Inclusion Criteria: * 1\. Age ≥ 18 years with anti-AQP4-IgG seropositive NMOSD as defined by 2015 NMOSD diagnostic criteria by IPND (International Panel for NMO Diagnosis). * 2\. Patients in the acute phase of NMOSD (definition of acute phase: new neurological symptoms or aggravation of existing symptoms within 30 days before received treatment, lasting at least 24 hours without fever), who had poor response to IVMP and without having received second-line therapies such as plasma exchange or intravenous immunoglobulin consequencely (Poor response is defined as a reduction in EDSS score of: I. \<1.0 from the baseline EDSS score when the baseline score was \<=5.5 II. \< 0.5 when the baseline EDSS score \> 5.5). * 3\. Patients who were approved for Efgartigimod treatment would be enrolled in the exposed group. * 4\. Expanded disability status scale (EDSS) score ≤ 8 and ≥ 2.5 before treatment. * 5\. Patients have given their written informed consent. Exclusion Criteria: * 1\. Lactating and pregnant females before treatment. * 2\. Participated in other interventional studies within 30 days before treatment. * 3\. Received plasma exchange, immunoadsorption, or intravenous immunoglobulin (IVIG） therapy within 1 month before treatment. * 4\. History of malignancies. * 5\. Combined with severe mental disorders and other conditions that unable to cooperate with follow-up. * 6\. After being evaluated by experts, patients with active hepatitis, active tuberculosis, or other special conditions which were ineligible to participate in this study.