What is the recommended emergency workup and initial treatment for a 19‑year‑old male with a 7‑day history of headache, recent weight loss, acute hallucinations, fear, abdominal cramping, and incoherent speech?

Emergency Workup and Initial Treatment

This 19-year-old male requires immediate empiric treatment for suspected autoimmune encephalitis while simultaneously pursuing urgent neuroimaging, metabolic workup, and infectious disease evaluation, as his constellation of subacute headache, psychiatric symptoms, hallucinations, and cognitive impairment strongly suggests NMDA receptor antibody-associated encephalitis or VGKC-complex antibody encephalitis.

Immediate Actions

Emergency Workup Priority

1. Neuroimaging First

   • Obtain urgent MRI brain with contrast (preferred) or non-contrast head CT if MRI unavailable
   • Look specifically for hippocampal high signal changes (seen in 60% of VGKC-complex cases, less common in NMDA receptor encephalitis where 77-90% have normal MRI) 1
   • Rule out mass lesions, hemorrhage, or hydrocephalus

2. Laboratory Investigations

   • Serum sodium level - critical as hyponatremia occurs in ~60% of VGKC-complex encephalitis 1
   • Complete metabolic panel (the abdominal cramping and weight loss may indicate metabolic derangement)
   • Serum autoimmune encephalitis panel: NMDA receptor antibodies and VGKC-complex antibodies 1
   • Toxicology screen (given age and acute psychiatric presentation)
   • CBC, inflammatory markers

3. Lumbar Puncture

   • Perform after neuroimaging rules out mass effect
   • CSF analysis for cell count, protein, glucose, NMDA receptor antibodies
   • CSF lymphocytosis (up to 500 cells/μL) supports NMDA receptor encephalitis 1
   • Note: CSF may be normal in VGKC-complex encephalitis; serum antibodies alone can establish diagnosis 1

4. EEG

   • Obtain to evaluate for seizure activity
   • May show epileptiform activity (50% early in NMDA receptor encephalitis) or generalized slowing (80% later) 1

5. Tumor Screening

   • Chest/abdomen/pelvis CT to identify associated malignancy
   • In young males with NMDA receptor encephalitis, tumor rate is lower than in females, but testicular ultrasound should be considered
   • Thymoma or small cell lung cancer possible in VGKC-complex cases (<10%) 1

Initial Treatment Algorithm

If NMDA Receptor Antibody Encephalitis Suspected (More Likely Given Age and Presentation)

The median age is 25 years with male:female ratio 1:2. The presentation matches the first phase: seizures, confusion, amnesia, psychosis, with headache and possible prodromal symptoms 1.

Immediate immunosuppression with combination therapy:

• Methylprednisolone 1 gram IV daily for 3-5 days PLUS
• Either plasma exchange OR IVIg 0.4 g/kg/day for 5 days
• Two immunosuppressive agents in combination are important for NMDA receptor encephalitis 1

If inadequate response:

• Consider rituximab or cyclophosphamide 1
• Plan for long-term immunosuppression (e.g., azathioprine) as 30% relapse rate even without tumor 1

If VGKC-Complex Antibody Encephalitis Suspected

The subacute history and potential hyponatremia fit this diagnosis 1.

Initial treatment:

• High-dose oral steroids (0.5 mg/kg/day prednisolone) if patient can take oral medications
• If acutely unwell: IVIg (0.4 g/kg/day) or plasma exchange in conjunction with steroids to accelerate improvement 1
• Continue steroids for 3-6 months until antibody levels normalize, then taper over 12 months 1

Critical Pitfalls to Avoid

• Do not delay empiric immunosuppression while awaiting antibody results - the clinical presentation warrants immediate treatment
• Do not use IVIg alone without steroids in VGKC-complex encephalitis - this may be less effective at reducing antibody levels with poorer outcomes 1
• Do not miss the tumor screening - this is essential in both conditions
• Do not assume this is primary psychiatric illness - the combination of headache, weight loss, and acute behavioral changes in a previously healthy young male demands organic workup

Supportive Care

• ICU admission likely needed given incoherent speech and potential for deterioration
• Seizure precautions and treatment if seizures occur
• Correct hyponatremia if present (but avoid overly rapid correction)
• Supportive care for hallucinations/agitation (low-dose benzodiazepines preferred over antipsychotics which may worsen dysautonomia)

The weight loss and abdominal cramping may represent prodromal symptoms or dysautonomia associated with the encephalitis rather than a separate process, but metabolic causes must still be excluded urgently.