19th January 2024

Background

Definition

Axial spondylitis is classified as a chronic seronegative spondyloarthropathy, primarily involving the axial skeleton. The hallmark clinical features are inflammatory back pain and spinal stiffness, which tend to respond well to non-steroidal anti-inflammatory drugs (NSAIDS). Ankylosing spondylitis (AS) is the name given to the radiological changes in the spine and sacroiliac joints, which can result from the progressive inflammatory changes. Further progression of the disease can result in spinal fusion and subsequent severe disability. HLA-B27 is found in 90% of patients with AS. It occurs most commonly between the ages of 20 and 30 years, and is more common in men than women.

Causes and pathophysiology

The aetiology of AS is unknown, but is thought to be a result of interaction between genetic and environmental factors. The heritability is estimated at 97%. The pathophysiological processes underlying AS include inflammation, erosion, and subsequent repair of cartilage. An increased number of osteoclasts are found in the axial skeleton of patients with AS.