Seronegative arthritis: Clinical

Seronegative arthritis refers to a group of four chronic diseases - ankylosing spondylitis, psoriatic arthritis, reactive arthritis, and enteropathic arthritis.

All of them are negative for rheumatoid factor, they’re all positive for HLA-B27, and they typically all run in families.

Another feature they share is that they usually affect the bones in the spine and nearby joints. That’s why they’re sometimes called seronegative spondyloarthritides, where spondylo means vertebra.

Other features include inflammatory back pain that causes morning stiffness which improves after 30 minutes of movement.

These diseases also cause peripheral arthritis that’s generally asymmetric, and axial arthritis like sacroiliitis and spondylitis, affecting the sacroiliac and vertebral joints, respectively.

Individuals also present enthesitis – meaning inflammation at the sites where tendons or ligaments insert into the bone and dactylitis, also known as sausage fingers.

They also cause extra-articular symptoms like involvement of the eyes with anterior uveitis, skin with psoriasis, the heart with aortic regurgitation or pericarditis, genitourinary involvement due to nerve compression at the spinal cord, and gastrointestinal involvement with inflammatory bowel disease - both Crohn's disease or ulcerative colitis.

Seronegative spondyloarthritides typically have a good response to NSAIDs and an elevated CRP in blood tests.

To meet the diagnostic criteria for seronegative spondyloarthritis, an individual has to have evidence of sacroiliitis on imaging plus one of these spondyloarthritis features, or HLA-B27 positivity plus two additional spondyloarthritis features.