A 35-year-old woman has relapsing-remitting MS. She is starting natalizumab. Which investigation MUST be done before initiation to stratify risk of a potentially fatal complication?
- A Anti-aquaporin-4 antibody
- B JC virus antibody index ✓
- C CSF oligoclonal bands
- D T-SPOT.TB (latent tuberculosis)
Correct answer: B. JC virus antibody index
Explanation
Natalizumab (anti-α4-integrin) carries a risk of progressive multifocal leukoencephalopathy (PML) caused by JC virus reactivation. Risk stratification using the anti-JCV antibody index is mandatory before and during treatment; high index (>0.9), prior immunosuppressant use, and prolonged natalizumab exposure (>2 years) all increase PML risk. Patients with high JCV index and extended treatment may be switched to safer alternatives. Anti-AQP4 is for NMOSD diagnosis; oligoclonal bands confirm MS diagnosis; TB screening is relevant for anti-TNF agents.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.