Psoriatic arthritis — SCE Rheumatology MCQ

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EasySpondyloarthropathiesPsoriatic arthritisSCE Rheumatology

A 45-year-old man with scalp psoriasis develops a swollen left knee, dactylitis of the second toe and pain at the Achilles insertion. RF and anti-CCP are negative. Nail examination shows pitting and onycholysis. Knee aspiration is sterile with inflammatory fluid. What is the most likely diagnosis?

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Reveal the answer and explanation

Correct answer: D — Psoriatic arthritis

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

Psoriatic arthritis is best because psoriasis with dactylitis, enthesitis, nail disease and seronegative inflammatory arthritis is typical of psoriatic arthritis. A is less suitable because gout can affect knees but would require urate crystals and would not explain nail psoriasis/dactylitis; B is less suitable because osteoarthritis is non-inflammatory and does not cause dactylitis; C is less suitable because septic arthritis should be excluded but sterile inflammatory fluid and multi-domain psoriatic features support PsA; D is less suitable because RA usually causes symmetric small-joint synovitis and anti-CCP may be positive. Clinical pearl: dactylitis is a high-value clue for peripheral spondyloarthritis.

Reference: BSR psoriatic arthritis biologic guideline 2022; NICE NG65