Ankylosing Spondylitis

Ankylosing spondylitis is an seronegative arthritis in which the sacroiliac joints and axial spine undergo a progressive ossification. Ankylosing spondylitis attacks the insertions points of ligaments, tendons, fascia, and fibrous joint capsules, (in contrast to rheumatoid arthritis, which attacks synovial membranes) and yields fibrosis and ossification of the insertions. Ligamentous attachments are collectively referred to as "entheses", hence "ensethopathy" is a common feature of ankylosing spondilitis.

The disease typically starts at the sacroiliac joint (SI joint is fused in the pelvic radiograph above), and spreads upwards, ossifying ligaments of the posterior facets of the spine and fusing vertebrae together, thus stiffening the spine and decreasing range of movement. Ossification within the anulus fibrosis (the fibro-cartilaginous ring that is wrapped around the outside of the intervertebral disk ) yields syndesmophytes (Spinal image above), radio-dense lines that connect vertebrae. With enough syndesmophyte formation, the whole spine has an undulating contour called "Bamboo Spine". A characteristic combination of bone erosion and formation occurs in this disease, such that the vertebrate become less concave and more 'square'. This squaring of the vertebral bodies is typical of ankylosing spondilitis.

Onset is typically in young people, usually in their late teens or twenties, and rarely after age of 35. Clinically, the disease is usually first noticed as a persistent backache which is not relieved by rest, and improves with exercise (unlike muscular back pain). It may also present as sciatica, peripheral joint pain, a painful sacroiliac joint or chest pain. Associated symptoms are anorexia, weight loss and a low grade fever. At its extreme, ankylosing spondylitis results in an ossification of the axial spine such that mobility is greatly reduced, and the spine becomes completely stiff and flexed, and the hips may be ankylosed as well, affecting gait. The spine is also at increased risk of fractures, further deforming the person's stance. However, only 20% of patients reach the extreme of a completely rigid spine.

Medical treatments include analgesia and an emphasis on posture and exercise to retain flexibility and range for as long as possible. Swimming is recommended.

Ankylosing spondylitis is associated with HLA-B27 in affected persons of European ancestry. However, only ca. 20% of people with HLA-B27 develop ankylosing spondylitis, so there are presumably other factors at work as well. Ethnic groups among whom HLA-B27 is rare also have a low incidence of ankylosing spondylitis