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MS – Fingolimod and PML Risk — SCE Neurology MCQ

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ModerateMultiple Sclerosis & CNS InflammationMS – Fingolimod and PML RiskSCE Neurology

A 40-year-old woman with RRMS on fingolimod presents with acute onset left-sided weakness and expressive aphasia. MRI brain shows a new large enhancing lesion in the right frontal lobe consistent with tumefactive demyelination. She has been on fingolimod for 5 years. Her lymphocyte count is 0.4 × 10⁹/L. What is the most important differential to exclude with this presentation?

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Correct answer: D — PML

Explanation lettering: C = shown as A · E = shown as C · A = shown as D · D = shown as E

In a patient on fingolimod (an S1P receptor modulator causing lymphopenia) with a new large lesion, PML must be excluded urgently. Although PML is rare with fingolimod, cases have been reported. CSF JC virus PCR should be performed. Tumefactive MS and PML can look similar on MRI, but PML lesions tend to be subcortical, non-enhancing, and involve U-fibres. The sustained lymphopenia increases the risk. B/C/D: These are differentials but PML is the most important to exclude given the immunosuppression. E: Stroke would not cause a ring-enhancing lesion.

Reference: Fingolimod SmPC; NICE TA254; ABN MS Guidelines (2022)