Macrophage activation syndrome — SCE Rheumatology MCQ

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HardPaediatric RheumatologyMacrophage activation syndromeSCE Rheumatology

Eight days after a second rituximab infusion, a patient develops fever, urticarial rash, severe arthralgia and low C3/C4 without bronchospasm or hypotension. What is the most likely adverse reaction?

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Correct answer: C — Rituximab-associated immune-complex serum sickness

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

E is correct. The delayed timing, fever, rash, polyarthralgia and hypocomplementaemia are characteristic of immune-complex serum sickness after rituximab. Immediate anaphylaxis and cytokine-release reactions occur during or shortly after infusion and usually feature respiratory or haemodynamic change. Delayed neutropenia does not explain rash, arthralgia and complement consumption. Viral infection remains a differential but does not account for the classic post-re-exposure pattern. Treatment depends on severity, and future rituximab exposure needs careful risk review rather than routine rechallenge.

Reference: UK MabThera summary of product characteristics: https://www.medicines.org.uk/emc/product/3801/smpc