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Dactylitis Ultrasound — SCE Rheumatology MCQ

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HardMusculoskeletal ImagingDactylitis UltrasoundSCE Rheumatology

A 48-year-old man with PsA has oligoarthritis with dactylitis of the 3rd toe. His rheumatologist performs an ultrasound of the dactylitic digit. What ultrasound finding is characteristic of dactylitis in PsA?

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Correct answer: D — Flexor tenosynovitis with diffuse digital soft-tissue inflammation

The best answer is “Flexor tenosynovitis with diffuse digital soft-tissue inflammation”. Ultrasound of a dactylitic digit in PsA characteristically shows flexor tenosynovitis (fluid and/or synovial thickening around the flexor tendon sheath) with surrounding soft tissue oedema and often adjacent joint synovitis and enthesitis. Dactylitis (sausage digit) is not simply joint swelling but a combination of synovitis tenosynovitis and soft tissue inflammation. Power Doppler signal indicates active inflammation. Understanding the composite pathology helps explain why dactylitis responds better to biologics (which address multiple inflammatory components) than to csDMARDs. The competing options represent related diagnoses, tests or treatments, but they do not match the decisive phenotype, safety constraint or management point in this stem.

Reference: OMERACT ultrasound definition of psoriatic dactylitis: https://pubmed.ncbi.nlm.nih.gov/18381777/