Ankylosing spondylitis and axial spondyloarthritis
An integral feature of the disease is inflammation involving ligament insertion sites and facet joints of the spine as well as the sacroiliac (SI) joints. The condition often affects HLA-B27 positive individuals and belongs to the group of seronegative spondyloarthropathies together with reactive enteroarthritis and uroarthritis, Reiter’s syndrome enthesitis-related arthritis (ERA), a subgroup of juvenile idiopathic arthritis psoriatic arthritis arthropathy associated with inflammatory bowel disease. Several of the above conditions may be encountered in members of the same family, and they may all lead to ankylosing spondylitis. The condition is termed idiopathic when it has become chronic and no causative agent has been detected, unlike in reactive arthritis.