Spondyloarthropathies.

The spondyloarthropathies include ankylosing spondylitis, reactive arthritis (including Reiter's syndrome), psoriatic arthritis, inflammatory bowel disease-associated spondyloarthropathy, and undifferentiated spondyloarthropathy. These diseases are linked by their association with the HLA-B27 gene and by the presence of enthesitis as the basic pathologic lesion. Additional clinical features include inflammatory back pain, dactylitis, and extra-articular manifestations such as uveitis and skin rash.