Ankylosing spondylitis (AS; previously known as Bechterew's disease, Bechterew syndrome, Marie Strümpell disease (from Greek ankylos, bent; spondylos, vertebrae), a form of Spondyloarthritis, is a chronic, inflammatory arthritis. It affects joints in the spine and the sacroilium in the pelvis, causing eventual fusion of the spine.

It is a member of the group of the spondyloarthropathies with a strong genetic predisposition. Complete fusion results in a complete rigidity of the spine, a condition known as bamboo spine.

Signs and symptoms

The typical patient is young, aged 18-30, with chronic pain and stiffness in the lower part of the spine, often with pain referred to one or other buttock or back of thigh from the sacroiliac joint early on. Pain is often severe on rest, and improves with physical activity. Men are affected more than women by a ratio about of 3:1. In 40% of cases, ankylosing spondylitis is associated with an inflammation of the white of the eye (iridocyclitis), causing eye pain and photophobia. Another common symptom is generalised fatigue. Less commonly aortitis, apical lung fibrosis and ectasia of the sacral nerve root sheaths may occur. As with all the seronegative spondarthropathies, lifting of the nails (onycholysis) may occur.

When the condition presents before the age of 18 it is relatively likely to cause pain and swelling of large limb joints, particularly the knee. The spine may be affected later on.

AS is one of a cluster of conditions known as seronegative spondarthropathies in which the characteristic pathological lesion is an inflammation of the enthesis (the insertion of tensile connective tissue into bone). Other forms of spondarthropathy are associated with ulcerative colitis, Crohn's disease, psoriasis, and Reiter's syndrome.

Pathophysiology

The association of AS with HLA-B27 suggests that the condition involves CD8 T cells, which interact with HLA-B. It is not proven that this interaction involves a self antigen and at least in the related Reiter's syndrome, which follows infections, the antigens involved are likely to be derived from intracellular microorganisms. There is, however, a possibility that CD4 T cells are involved in an aberrant way, since HLA-B27 appears to have a number of unusual properties, including possibly an ability to interact with T cell receptors in association with CD4.

There has been a longstanding claim that AS arises from a cross-reaction between HLA-B27 and antigens of the Klebsiella bacterial strain (Tiwana et al. 2001).The problem with this idea is that no such cross reactivity with B27 has been found (I.e. although antibody responses to klebsiella may be increased, there is no antibody response to B27, so there seems to be no cross reactivity.) Particular authorities argue that elimination of the prime nutrients of Klebsiella (starches) would decrease antigenemia and improve the musculoskeletal symptoms. However, as Khan (2002) argues, evidence for a correlation between Klebsiella and AS is circumstantial so far, and that the efficacy of low-starch diets has not yet been scientifically evaluated. Similarly, Toivanen (1999) found no support for the role of klebsiella in the etiology of primary AS.