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Rheumatoid arthritis flare versus infection — SCE Rheumatology MCQ

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ModerateInflammatory ArthritisRheumatoid arthritis flare versus infectionSCE Rheumatology

A 69-year-old man with rheumatoid arthritis on abatacept develops an acutely swollen right knee. He is afebrile but CRP is 112 mg/L and the knee is very painful with restricted movement. He had a steroid injection into the same knee 3 months earlier. There are no other swollen joints. What is the most appropriate investigation?

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

Reveal the answer and explanation

Correct answer: A — Urgent joint aspiration for microscopy, culture and crystals

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

Urgent joint aspiration for microscopy, culture and crystals is best because monoarthritis in an immunosuppressed patient requires aspiration to exclude septic arthritis and crystal disease. A is less suitable because anti-CCP confirms RA phenotype but not the cause of the hot joint; B is less suitable because increasing abatacept would worsen untreated infection risk; C is less suitable because prednisolone before aspiration may mask infection; E is less suitable because delayed MRI is not appropriate for acute suspected septic arthritis. Clinical pearl: culture and crystal analysis are both needed because crystal arthritis and infection can coexist.

Reference: BSR hot swollen joint guideline; BSR bDMARD safety guideline 2019