A 32-year-old woman with relapsing-remitting MS is on natalizumab for 3 years. Her JC virus antibody index rises to 3.6 (high). She has experienced no PML. What is the most important risk management decision?
- A Switch to a different high-efficacy therapy (e.g., ocrelizumab) to avoid PML risk ✓
- B Continue natalizumab; JC index does not affect management unless symptoms develop
- C Add IVIG to cover against JC virus infection
- D Perform lumbar puncture and start prophylactic antiviral therapy
Correct answer: A. Switch to a different high-efficacy therapy (e.g., ocrelizumab) to avoid PML risk
Explanation
JC virus antibody index >1.5 combined with natalizumab use >24 months and prior immunosuppressive therapy gives PML risk of >1:100. At index >3.0 and duration >2 years, the PML risk becomes prohibitively high and natalizumab should be discontinued. Switching to an alternate high-efficacy therapy (ocrelizumab, alemtuzumab, or cladribine) preserves disease control while eliminating PML risk. There is no approved antiviral prophylaxis for PML. MRI surveillance every 3 months may detect early asymptomatic PML.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.