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MS – Early PML Detection — SCE Neurology MCQ

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HardMultiple Sclerosis & CNS InflammationMS – Early PML DetectionSCE Neurology

A 48-year-old woman with RRMS who has been seizure-free for 2 years on natalizumab develops a new, subtle right arm clumsiness and mild cognitive slowing over 3 weeks. Her JCV antibody index is 2.8. MRI brain shows a new, non-enhancing lesion in the left frontal subcortical white matter with high signal on DWI extending beyond the T2 lesion margin. What is the most concerning diagnosis?

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Correct answer: D — Progressive multifocal leukoencephalopathy

In a natalizumab-treated patient with a high JCV antibody index (>1.5), subacute cognitive/motor decline with a new lesion showing DWI signal extending beyond the T2 margin (the so-called 'DWI rim') without gadolinium enhancement is highly suspicious for PML. PML lesions typically involve the subcortical U-fibres, are non-enhancing initially, and show progressive enlargement. A: MS relapses typically enhance with gadolinium. C: Stroke is acute and would show restricted diffusion confined to a vascular territory. D: CNS lymphoma typically enhances intensely. E: Tumefactive demyelination usually has ring enhancement.

Reference: ABN MS Guidelines (2022); Wattjes et al. PML MRI Consensus (2015)