Efgartigimod in Anti-NMDA Receptor Encephalitis.

Inclusion Criteria: 1. Age ≥18 years old, male or female; 2. Diagnosed as anti-NMDAR encephalitis, diagnostic criteria as follows: 1. At least one of the following six major symptoms: * Abnormal (mental) behavior or cognitive dysfunction * Speech dysfunction (verbal urgency, hypospeech, mutism) * Seizures * Movement disorders, dyskinesias, or postural rigidity/abnormalities * Decreased level of consciousness * Autonomic dysfunction or central hypoventilation in the presence of one or more of the six major symptoms; 2. Positive anti-NMDAR IgG antibody: Diagnosis should be based on CSF antibody positivity using CBA. If only serum samples are available for testing, a positive CBA result must be supplemented with TBA on cultured neurons for definitive confirmation. Serum positivity at low titers (1:10) is not diagnostically significant. c．Reasonable exclusion of other etiologies. 3. Patients with newly diagnosed or relapsed anti-NMDAR encephalitis who scored ≥2 on the mRS (5 patients each with mRS scores of 2-5); * Newly diagnosed patients must not have received any prior immunosuppressive therapy. * For relapsed patients: 1. For subjects receiving rituximab, treatment must have commenced at least 2 months prior to screening, with the final dose administered no less than 4 weeks before randomization, and no improvement in mRS score within the 4 weeks preceding randomization. 2. For subjects receiving other immunosuppressive agents (i.e., mycophenolate mofetil, cyclophosphamide, or azathioprine), treatment must have been ongoing for at least 2 months prior to screening, the dose must have been stable for at least 4 weeks prior to screening, and there must have been no improvement in the mRS score within 4 weeks prior to randomization. 3. For subjects receiving oral corticosteroids, those receiving a stable daily dose of ≥20 mg of prednisolone (or its equivalent) with no increase in steroid dosage within 4 weeks prior to screening, and no improvement in mRS score within 4 weeks prior to randomization. 4. For subjects receiving repeated courses (pulse therapy) of acute first-line therapy, treatment must be completed \>2 weeks prior to randomization (baseline visit). 4. Study subjects had received at least 3 days of glucocorticoid therapy at a dose of 500-1000 mg MP daily within 2 weeks prior to enrollment (baseline visit). They had transitioned to oral corticosteroid therapy and stable doses of non-steroidal immunosuppressive agents (NISIT) (limited to relapsed patients), and had not received IVIG or plasma exchange. 5. For women of childbearing potential should use effective contraception during treatment and for at least 3 months after the last dose of Efgartigimod. 6. Ability to sign an informed consent form, which includes agreeing to comply with the requirements and restrictions outlined in the informed consent form and this protocol. Exclusion Criteria: Subjects should be excluded from the study if they meet any of the following criteria: 1. Presence of any untreated teratoma or thymoma at baseline visit. Detection of teratoma or thymoma prior to or during the screening period is permitted if the disease is considered cured following treatment (typically surgical resection) within 1 week before baseline. 2. Known allergy to any component of the study drug or any other anti-FcRn drug. 3. Received IVIG or PE therapy within 2 weeks prior to screening. 4. Research participants with clinically significant active infections (including unresolved or inadequately treated infections) as assessed by the investigator. 5. Malignancies requiring chemotherapy. 6. Total IgG level ≤6 g/L in study subjects during screening visits. 7. Pregnancy 8. Patients with severe underlying conditions such as cardiac insufficiency, arrhythmia, or coagulation disorders.