How should NMDA‑receptor antibody‑positive autoimmune encephalitis be managed, including first‑line immunotherapy, tumor screening, and second‑line treatment?

Management of NMDA Receptor Antibody-Positive Autoimmune Encephalitis

Start high-dose corticosteroids immediately once infection is ruled out, and if the presentation is severe (refractory seizures, severe dysautonomia, ICU-level illness), combine corticosteroids with IVIG or plasma exchange from the outset rather than waiting for treatment failure. 1

First-Line Immunotherapy

Initial Treatment Selection

• High-dose intravenous corticosteroids (typically methylprednisolone) are the preferred first-line agent for NMDAR-antibody encephalitis 1
• Begin immunotherapy as soon as basic CSF results exclude infection (based on cell count patterns), without waiting for antibody confirmation 1
• For severe presentations (new-onset refractory status epilepticus, severe dysautonomia, or ICU admission), initiate combination therapy immediately with corticosteroids plus IVIG or corticosteroids plus plasma exchange 1

Alternative First-Line Options

• IVIG is preferred over plasma exchange in agitated patients and those with bleeding disorders 1
• Plasma exchange (5-10 sessions every other day) is preferred in patients with severe hyponatremia, high thromboembolic risk (including cancer), or associated demyelination 1
• Plasma exchange combined with corticosteroids showed better modified Rankin Scale improvement than corticosteroids alone in retrospective data 1

Sequential First-Line Escalation

• If no clinical, radiological, or electrophysiological improvement occurs by the end of the initial treatment cycle, add IVIG or plasma exchange to corticosteroids 1
• 62% of expert clinicians add a different first-line therapy if the initial agent fails, while only 26% proceed directly to second-line agents 1

Tumor Screening

Initial Screening Protocol

• Perform CT chest, abdomen, and pelvis with contrast in all NMDAR-antibody encephalitis patients as initial cancer screening 1
• Young and middle-aged adults with typical NMDAR-antibody encephalitis presentation require transvaginal or transabdominal pelvic ultrasound (or testicular ultrasound in males) to screen for teratoma 1

Additional Screening When Initial CT is Negative

• Mammogram (and breast MRI if high suspicion) for female patients, particularly those not up-to-date with screening or with strong family history 1
• Whole body FDG-PET scan when initial CT is negative but cancer suspicion remains high based on demographics (smoking history, advanced age) or if CT contrast is contraindicated 1
• Pelvic MRI if ultrasound is equivocal for teratoma detection 1

Second-Line Treatment

Timing and Indications

• Initiate second-line agents 2-4 weeks after completion of combined first-line therapy if no meaningful clinical or radiological improvement occurs 1, 2
• Some clinicians may choose earlier initiation (around 2 weeks after first-line initiation) for severe or refractory cases 1, 2

Agent Selection

• Rituximab is the preferred second-line agent for NMDAR-antibody encephalitis (chosen by 80% of expert clinicians), as it is less toxic than cyclophosphamide and specifically targets antibody-mediated autoimmunity 1
• Common rituximab dosing: 375 mg/m² weekly for 4 weeks, or two doses of 1000 mg given 2 weeks apart 1
• Cyclophosphamide (600-1000 mg/m²) is reserved for cell-mediated autoimmunity (classical paraneoplastic syndromes with intracellular antibodies) 1
• Rituximab use has increased from 13.5% (2007-2013) to 28.3% (2013-2019), concurrent with falling relapse rates from 22% to 10.9% 3

Refractory Disease Options

• If no improvement with conventional second-line therapies, consider tocilizumab (IL-6 inhibitor) or bortezomib (proteasome inhibitor), though evidence is limited 1
• Alternating or repeated use of both rituximab and cyclophosphamide may be required in some refractory cases 4

Bridging and Maintenance Therapy

• Start bridging therapy with gradual oral prednisone taper, monthly IVIG, or monthly IV methylprednisolone after acute treatment 1
• Maintenance immunosuppression beyond 6 months (rituximab redosing or mycophenolate mofetil) is generally not required except for patients with severe courses, prolonged impairments, or relapsing disease 2
• Maintenance IVIG for 6 months or more is associated with reduced relapse risk but paradoxically associated with poor functional outcome, likely reflecting selection bias toward more severe cases 3

Prognostic Factors and Pitfalls

Predictors of Good Outcome

• Early treatment initiation (within 30 days of symptom onset) is the strongest modifiable predictor of good functional outcome 3, 5
• Adolescent age at onset (versus extremes: <2 years or ≥65 years) 3
• Avoiding ICU admission correlates with better outcomes, though this reflects disease severity 3, 5

Predictors of Poor Outcome

• Age younger than 2 years or 65 years or older at onset 3
• Extreme delta brush pattern on EEG 3
• Lack of immunotherapy within first 30 days 3
• ICU admission requirement 3, 5

Common Pitfalls

• Do not delay immunotherapy waiting for antibody confirmation—clinical suspicion alone warrants treatment initiation 1
• Do not use maintenance IVIG routinely—it is associated with worse outcomes except in specific high-risk scenarios 3
• Recovery may take up to 18 months; do not prematurely conclude treatment failure 5
• Relapses occur in 12% within 2 years but are typically less severe than initial episodes (67% of relapses) 5
• Second-line immunotherapy significantly improves outcomes (OR 2.69) when first-line fails—do not withhold escalation 5