Ankylosing spondylitis (AS)


Ankylosing spondylitis (AS) (also called Bechterew's disease) is one of many forms of inflammatory arthritis, the most common of which is rheumatoid arthritis. Ankylosing spondylitis primarily causes inflammation of the joints between the vertebrae of your spine and the joints between your spine and pelvis (sacroiliac joints). However, ankylosing spondylitis may also cause inflammation and pain in other parts of your body:

  • Where your tendons and ligaments attach to bones
  • Joints between your ribs and spine
  • Joints in your hips, shoulders, knees and feet
  • Your eyes

As ankylosing spondylitis worsens and the inflammation persists, new bone forms as a part of the body's attempt to heal. Your vertebrae begin to grow together, forming vertical bony outgrowths (syndesmophytes) and becoming stiff and inflexible. Fusion can also stiffen your rib cage, restricting lung capacity and function.

Also called spondylitis or rheumatoid spondylitis, ankylosing spondylitis is a chronic condition. Treatments can decrease your pain and lessen your symptoms. Effective treatment may also help prevent complications and physical deformities.


Your condition may change over time, with symptoms getting worse, improving or completely stopping at any point. Early signs and symptoms may include pain and stiffness in your lower back and hips – which is often worse in the morning, at night and after periods of inactivity. Over time, the pain and stiffness may progress up your spine and to other joints, such as those in your hips, shoulders, knees and feet.

In advanced stages, the following signs and symptoms may develop:

  • Restricted expansion of your chest
  • Chronic stooping
  • Stiff, inflexible spine
  • Fatigue
  • Loss of appetite
  • Weight loss
  • Eye inflammation (iritis)
  • Bowel inflammation


Ankylosing spondylitis has no known specific cause, though genetic factors seem to be involved. In particular, people who have a gene called HLA-B27 are at significantly increased risk of developing ankylosing spondylitis.

Risk factors

Genetics may play a role in the development of ankylosing spondylitis. In fact, the majority of people with this condition have the HLA-B27 gene. Having this gene doesn't mean that you'll acquire ankylosing spondylitis – no more than 2 percent of people with this gene develop the condition – but it may make you more susceptible to the disease.

If you test positive for the HLA-B27 gene, are younger than 40 and have a family member with ankylosing spondylitis, you have about a one in five chance of developing the condition. However, if you're older than 40, your chances of acquiring ankylosing spondylitis are low. If you have ankylosing spondylitis, you have about a 50 percent chance of passing the HLA-B27 gene on to your children if you have the gene.

Ankylosing spondylitis affects males more often, and its onset generally occurs between the ages of 16 and 40. In the United States, ankylosing spondylitis is most common among some American Indian tribes.