How do the seronegative spondyloarthropathies differ from Rhemuatoid Arthritis?
Ankylosing spondylitis (AS), psoriatic arthritis (PA), reactive arthritis (Reiter syndrome), and enteropathic arthritis (associated with inflammatory bowel disease) are major types of seronegative spondyloarthropathy. Patients with seronegative spondyloarthropathy usually lack presence of rheumatoid factor (RF) on blood tests (hence the term seronegative ), whereas RF is characteristically present in RA. The HLA-B27 antigen is frequently present on blood tests in seronegative spondyloarthropathy. In seronegative spondyloarthropathies, involvement of the DIP joints, sacroiliac joints, and spine (with syndesmophyte formation in AS or parasyndesmophyte formation in PA and reactive arthritis) is common, often in association with productive bony changes and enthesopathy. These imaging features are uncommonly seen in RA. With long-standing disease, any patient with seronegative spondyloarthropathy may develop ankylosis of the sacroiliac joints and spine, which is classically associated with AS