Autoimmune encephalitis presenting as first-episode psychosis (MEQ)

(i) Red flags and differential. Red flags: subacute (days–weeks) first psychosis after viral-like prodrome; explosive tempo; speech reduction/mutism; orofacial dyskinesias; limited response to antipsychotics; young woman. Leading diagnosis: anti-NMDAR autoimmune encephalitis / probable autoimmune psychosis pending confirmation. Discriminators from primary FEP: rapid multistage evolution, hard neurologic signs (speech, movement), normal MRI does not exclude AE, need for EEG/CSF/Abs and immunotherapy rather than antipsychotic escalation alone.^[1][6][4]

(ii) Investigations. Urgent neurology co-management. EEG (encephalopathic slowing; extreme delta brush supportive if present). MRI already done — normal MRI does not stop the pathway. LP: cell count, protein, glucose, OCB, infection panel including HSV PCR as indicated; paired serum and CSF neuronal cell-based assays (NMDAR and broader panel as advised). Do not rely on serum-only commercial tests. Metabolic baseline, pregnancy test. Tumour search: pelvic ultrasound/MRI for ovarian teratoma. Apply Graus possible/probable AE and Pollak frameworks to document rationale.^[2][5][4]

(iii) Immunotherapy and tumour. When probable AE criteria are met, start first-line immunotherapy without waiting indefinitely for serology: high-dose IV methylprednisolone (commonly about 1 g daily for 3–5 days per local protocol), IVIG (commonly total 2 g/kg over 2–5 days), and/or plasma exchange (often about 5 exchanges). If inadequate response: second-line rituximab and/or cyclophosphamide under specialist protocols. Parallel teratoma resection if found — disease-modifying. Titulaer: early treatment and tumour removal improve outcomes.^[3][5][6]

(iv) Psychotropics, capacity, family. Stop the "depot-only" plan. Use benzodiazepines for catatonia/agitation; cautious lowest-effective antipsychotic only for safety as a bridge — not definitive therapy. Assess capacity for LP/immunotherapy; if lacking, use local least-restrictive legal framework for emergency investigation/treatment (do not invent foreign section numbers). Explain to family: treatable brain inflammation, need for CSF and possible immunotherapy, hope for recovery over months with early care, psychiatry remains involved for symptoms and aftercare.^[4][3][5]