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CPPD diagnosis — SCE Rheumatology MCQ

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EasyMusculoskeletal investigationsCPPD diagnosisSCE Rheumatology

An 83-year-old woman develops acute wrist pain and swelling two days after abdominal surgery. Examination shows a hot, tender wrist with an effusion. A radiograph demonstrates chondrocalcinosis of the triangular fibrocartilage. Which investigation is most appropriate to confirm the suspected diagnosis while addressing the principal urgent differential diagnosis?

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Correct answer: C — Synovial fluid microscopy for crystals, with Gram stain and culture

Urgent joint aspiration is the most appropriate investigation. Identification of positively birefringent, rhomboid calcium pyrophosphate crystals supports acute CPP crystal arthritis, for which advanced age, surgery and triangular fibrocartilage chondrocalcinosis are characteristic clues. Because this is an acutely hot, swollen joint following surgery, synovial fluid must also be sent for Gram stain and culture to investigate septic arthritis; finding crystals does not by itself exclude concomitant infection. HLA-B51 supports assessment for Behçet disease, nerve conduction studies investigate neuropathy, and anti-dsDNA is used when systemic lupus erythematosus is suspected. Serum urate neither diagnoses CPPD nor safely distinguishes crystal arthritis from infection.

Reference: Zhang W et al. European League Against Rheumatism recommendations for calcium pyrophosphate deposition. Part I: terminology and diagnosis. Ann Rheum Dis. 2011;70:563–570. https://pubmed.ncbi.nlm.nih.gov/21216817/