Radiologic case study. Seronegative spondyloarthropathy associated with Crohn's disease.

Seronegative arthropathies are a heterogeneous group of arthropathic disorders with negative rheumatoid factors and varying association with the HLA-B27 phenotype. The distribution of involvement and pattern of presentation within this group is variable. However, these disorders share common features of aggressive erosions, bone density preservation, and proliferative bony response to inflammation. These features along with asymmetric involvement of the appendicular skeleton, sacroiliitis, and spine abnormalities usually allow differentiation from rheumatoid arthritis and other inflammatory arthritides based on imaging studies.