A 52-year-old woman presents with acute onset of severe headache, confusion, and seizures. MRI brain shows limbic encephalitis. Anti-NMDA receptor antibodies are detected. Which is the most common malignancy associated with this paraneoplastic syndrome?

Question

Accepted Answer

D. Ovarian teratoma. ## Anti-NMDA Receptor Encephalitis

### Clinical Presentation
The patient exhibits the classic triad of anti-NMDA receptor encephalitis:
- **Psychiatric phase:** Behavioral changes, paranoia, hallucinations
- **Movement disorder phase:** Dystonia, choreoathetosis, rigidity
- **Autonomic/seizure phase:** Seizures, autonomic instability, hypoventilation
- **Imaging:** Limbic encephalitis pattern on MRI (T2/FLAIR hyperintensities in medial temporal lobes)

### Antibody-Malignancy Association

| Antibody | Most Common Malignancy | Frequency | Demographics |
|---|---|---|---|
| Anti-NMDA receptor | Ovarian teratoma | 40–50% (young women) | Females <50 years |
| Anti-NMDA receptor | Breast cancer | 10–15% | Older women |
| Anti-NMDA receptor | Lung cancer | 5–10% | Smokers |
| Anti-NMDA receptor | Gastric cancer | <5% | Rare |

**High-Yield:** In young women with anti-NMDA receptor encephalitis, **ovarian teratoma** is the most common underlying malignancy (40–50% of cases). These are often immature teratomas containing neural tissue that expresses NMDA receptors.

### Pathophysiology
Anti-NMDA receptor antibodies bind to the NR1 subunit of NMDA receptors on neuronal membranes. This causes:
1. Antibody-mediated internalization of NMDA receptors
2. Reduced synaptic transmission
3. Excitotoxic neuronal death
4. Limbic encephalitis and seizures

### Clinical Pearl
**Key Point:** Anti-NMDA receptor encephalitis is one of the most common autoimmune encephalitis syndromes. In a young woman with this diagnosis, pelvic imaging (ultrasound or CT) to screen for ovarian teratoma is mandatory.

**Warning:** Ovarian teratomas in this context are often **immature** and may be difficult to detect on imaging. Repeat imaging or even diagnostic laparoscopy may be needed.

### Diagnostic Approach
1. **Serology:** Anti-NMDA receptor (IgG) in serum and CSF
2. **CSF:** Lymphocytic pleocytosis, elevated protein, oligoclonal bands
3. **Brain MRI:** Limbic encephalitis (medial temporal lobe involvement)
4. **Pelvic imaging:** Transvaginal ultrasound, pelvic CT/MRI (teratoma screening)
5. **Pathology:** Ovarian biopsy if imaging inconclusive

### Management
1. **Immunotherapy:** First-line = IVIg + plasmapheresis ± corticosteroids
2. **Tumor removal:** Surgical resection of ovarian teratoma (definitive treatment)
3. **Seizure control:** Antiepileptic drugs
4. **Second-line:** Rituximab, cyclophosphamide if inadequate response

**Mnemonic:** **NMDA-OT** = NMDA receptor antibodies + Ovarian Teratoma in young women.

Answer

A. Lung cancer

Answer

B. Breast cancer

Answer

C. Gastric cancer

A 52-year-old woman presents with acute onset of severe headache, confusion, and seizures. MRI brain shows limbic encephalitis. Anti-NMDA receptor antibodies are detected. Which is the most common malignancy associated with this paraneoplastic syndrome?

Explanation

Anti-NMDA Receptor Encephalitis

Clinical Presentation

Antibody-Malignancy Association

Pathophysiology

Clinical Pearl

Diagnostic Approach

Management

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Antibody	Most Common Malignancy	Frequency	Demographics
Anti-NMDA receptor	Ovarian teratoma	40–50% (young women)	Females <50 years
Anti-NMDA receptor	Breast cancer	10–15%	Older women
Anti-NMDA receptor	Lung cancer	5–10%	Smokers
Anti-NMDA receptor	Gastric cancer	<5%	Rare