A 42-year-old man presents with inflammatory low back pain for 2 years that improves with exercise and worsens with rest. He reports alternating buttock pain. Schober test is 3 cm. X-ray pelvis shows bilateral sacroiliitis (grade 3). Which additional finding most strongly supports a diagnosis of ankylosing spondylitis over other causes of sacroiliitis?

• A Positive rheumatoid factor
• B History of recent genitourinary infection
• C Elevated serum uric acid
• D Presence of HLA-B27 ✓

Explanation

HLA-B27 is present in approximately 90% of patients with ankylosing spondylitis and is a major classification criterion. Rheumatoid factor is negative in AS (seronegative spondyloarthropathy). Recent GU infection suggests reactive arthritis. Elevated uric acid is unrelated to sacroiliitis. The modified New York criteria require radiographic sacroiliitis plus clinical criteria (inflammatory back pain, limited lumbar motion, or reduced chest expansion).

Reference: Kelley and Firestein's Textbook of Rheumatology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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