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Behcet Disease — SCE Rheumatology MCQ

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EasyVasculitisBehcet DiseaseSCE Rheumatology

A 38-year-old woman with recurrent oral and genital ulceration undergoes a sterile needle-prick pathergy test during assessment for Behçet disease. At 48 hours, there is a 3 mm erythematous, indurated papule at the puncture site. Which local reaction is conventionally classified as a positive pathergy test?

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Correct answer: A — An erythematous induration or sterile papulopustule at least 2 mm in diameter at 48 hours

Option A is correct. A positive pathergy response is conventionally an erythematous induration or sterile papule/pustule measuring at least 2 mm when read at 48 hours after sterile needle trauma. The 3 mm indurated papule in this patient therefore represents a positive result. Pathergy supports Behçet classification but is not independently diagnostic, and its sensitivity varies with geography, disease activity and testing technique. A large pustule or 10 mm reaction is not required, while erythema alone is insufficient under the stated size-based criterion. Ulceration is not required. Although the forearm is commonly used, anatomical site alone does not determine positivity. The original answer label remains correct, but the threshold has been repaired from greater than 2 mm to at least 2 mm and the timing standardised to 48 hours.

Reference: Deniz R et al. Improved sensitivity of the skin pathergy test with polysaccharide pneumococcal vaccine antigens in the diagnosis of Behçet disease. Rheumatology (Oxford). 2023;62:1903–1909. https://pubmed.ncbi.nlm.nih.gov/36171681/