A 29-year-old man notes burning pain on urination with a urethral discharge that has persisted for 3 days. A sample of the exudate is positive by ELISA for Chlamydia trachomatis. The man has increasing stiffness of the knees and ankles and lower back pain 3 weeks later. A radiograph of the lumbar spine shows narrowing with sclerosis of the sacroiliac joints. One month later, he develops painful erythema of the glans penis, and the conjunctivae are red. A follow-up examination shows a slightly irregular heart rate and a murmur suggestive of aortic regurgitation. The back pain continues off and on for 5 more months. Which of the following test results is most likely to be positive in this man?
The combination of nongonococcal urethritis, arthritis, and conjunctivitis suggests reactive arthritis, one of the spondyloarthropathies; the changes in the spine can resemble ankylosing spondylitis and can be equally debilitating. ANCA is indicative of various forms of vasculitis, such as granulomatous vasculitis and microscopic polyangiitis. The ANA test result is positive in many autoimmune diseases, such as systemic lupus erythematosus (SLE), but it is not a feature of spondyloarthropathies. Lyme disease can include large joint arthritis, but not urethritis or conjunctivitis. Rapid plasma reagin (RPR) is a screening test for syphilis, which can include arthritis of large joints (Charcot joint) in the tertiary form, but it takes decades to develop. Rheumatoid factor is a feature of rheumatoid arthritis, which initially manifests more commonly in small joints of the hands and feet. U1-RNP is a marker for mixed connective tissue disease, which has features of rheumatoid arthritis, scleroderma, polymyositis, and SLE; arthralgias are not accompanied by joint destruction or deformity.
ANCA
ANA
HLA-B27 genotype
Anti-Borrelia antibodies
Misc.