PML on Natalizumab – Diagnosis — SCE Neurology MCQ

Instant feedback + full explanation. One question, done properly.

HardMultiple Sclerosis & CNS InflammationPML on Natalizumab – DiagnosisSCE Neurology

A 40-year-old woman with MS on natalizumab develops progressive cognitive decline and a subtle left-sided weakness over 2 weeks. MRI brain shows a new large white matter lesion in the right frontal lobe that does NOT enhance with gadolinium but shows restricted diffusion on DWI. JCV DNA is detected in CSF by PCR. What is the diagnosis?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Progressive multifocal leukoencephalopathy (PML) — confirmed by CSF JCV PCR positivity

PML is caused by JCV reactivation in immunosuppressed patients. Key MRI differences from MS: PML lesions are typically large, affecting subcortical U-fibres, do NOT enhance with gadolinium (unlike MS which typically enhances), show restricted diffusion on DWI, and are progressive. CSF JCV DNA PCR confirms the diagnosis. Management: stop natalizumab immediately, plasma exchange (to accelerate natalizumab clearance), and supportive care. Immune reconstitution inflammatory syndrome (IRIS) may occur as the immune system recovers. A: The non-enhancing pattern with DWI restriction and JCV DNA confirms PML, not MS. C: Not stroke (progressive course). D: Not tumour. E: ADEM is monophasic.

Reference: ABN MS Guidelines; McGuigan et al. PML in Natalizumab