A 22-year-old woman presents with a 3-week history of fever, headache, and progressive behavioral changes including paranoid delusions and agitation. Over the past week, she has developed involuntary orofacial movements and seizures. EEG shows the pattern marked **A** in the diagram — high-amplitude rhythmic delta waves with superimposed beta activity. CSF analysis reveals lymphocytic pleocytosis with oligoclonal bands. Serum and CSF anti-NMDA receptor IgG antibodies are positive. Which of the following is the MOST IMPORTANT next step in management?

Explanation

## Why pelvic ultrasound/MRI with tumor removal is correct The extreme delta brush (EDB) pattern marked **A** is pathognomonic for anti-NMDA receptor encephalitis. The clinical anchor states that ovarian teratoma is present in 40–60% of adult women with this diagnosis and is the PRIMARY TRIGGER of the autoimmune response. Tumor removal (oophorocystectomy) is the FIRST-LINE and MOST IMPORTANT intervention because it eliminates the source of antigen-driven B-cell and T-cell activation. Even microscopic teratomas (<10 cm) must be identified and removed. Immunotherapy (methylprednisolone, IVIG, rituximab) is essential but SECONDARY to tumor removal; outcomes are significantly better when tumor is removed early. The EDB pattern, though pathognomonic and predicting prolonged illness, is a diagnostic marker—not a treatment target. Pelvic imaging must precede or accompany immunotherapy initiation. ## Why each distractor is wrong - **High-dose IV methylprednisolone and IVIG, with rituximab reserved for relapse**: While immunotherapy is critical and should be started promptly, it is SECOND-LINE management. Tumor removal is FIRST-LINE and must be prioritized. Starting immunotherapy without searching for and removing the teratoma allows the antigen source to persist, reducing efficacy and prolonging recovery. - **Antiepileptic drugs and antipsychotics as sole therapy**: Symptomatic management alone is insufficient. Anti-NMDAR encephalitis requires immunotherapy and tumor removal to address the underlying autoimmune pathogenesis. Seizures and psychiatric symptoms will not resolve without treating the cause. - **Lumbar puncture with repeat CSF analysis to confirm oligoclonal bands**: CSF analysis has already been performed and anti-NMDAR IgG is positive. Repeat lumbar puncture delays definitive management. The diagnosis is confirmed; the next step is to identify and remove the tumor source. **High-Yield:** Anti-NMDA receptor encephalitis in young women = search for ovarian teratoma first; tumor removal is first-line, immunotherapy is second-line. EDB on EEG is pathognomonic but does not change management priority. [cite: Dalmau et al. Lancet Neurol 2008, 2019 review; Schmitt SE et al. Neurology 2012; Harrison's Principles of Internal Medicine, 21st ed.]