Ankylosing Spondylitis

About Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a type of arthritis that mainly affects the spine. The joints of the spine and the joints between the spine and pelvis become inflamed. This results in pain and stiffness in the neck and back.

Spondylitis is the medical term for inflammation of the joints of the spine.

Ankylosis is the medical term for the stiffening caused by the inflammation.

One in 2000 people in the UK have AS. It is more common and often more severe in men than in women, and usually begins between the ages of 16 and 40 years


  • The cause of AS is not known, but the condition may be partly hereditary (passed down from parents to children).
  • There is a strong association between ankylosing spondylitis and a gene called HLA-B27.
  • It is thought that HLA-B27 causes the body’s immune system to attack the joints of the spine, which is what causes the inflammation.
  • Therefore ankylosing spondylitis is often thought of as an autoimmune disease – a disease in which the person’s own immune system attacks their body.
  • However, not everyone with the HLA-B27 gene develops ankylosing spondylitis.

The spine

  • The spine is made up of 24 bones called vertebrae, plus the sacrum and coccyx. These are linked with joints.
  • There are three main sections of vertebral spine: cervical (neck), thoracic (chest) and lumbar (lower back).
  • In the thoracic section, each vertebrae also has joints with 12 pairs of ribs.
  • Below the lumbar spine is the sacrum, which is actually five vertebrae fused into one bone. This forms a joint with the pelvis (hip bone) on either side, called the sacroiliac joint.

Any of these joints in the spine may be affected by AS.

How inflammation occurs and persists in different organs and joints in ankylosing spondylitis is a subject of active research

Each individual tends to have their own unique pattern of presentation and activity of the illness.

The initial inflammation may be a result of an activation of the body’s immune system by a bacterial infection or a combination of infectious microbes. Once activated, the body’s immune system becomes unable to turn itself off, even though the initial bacterial infection may have long subsided.

Chronic tissue inflammation resulting from the continued activation of the body’s own immune system in the absence of active infection is the hallmark of an inflammatory autoimmune disease


Typically, the symptoms of ankylosing spondylitis come and go. AS often starts at the sacroiliac joint causing lower back pain, which is usually worse at night and in the morning, and relieved by gentle activity. There may also be pain in the buttocks or down the backs of the thighs. Typically, the back is stiff in the mornings.

In up to one quarter of people with AS, other joints are affected. These include the hips, knees and shoulders, and occasionally the smaller joints in the hands and feet. This may cause aching and swelling.

The symptoms of AS vary in different people. Some people may only get a few mild aches and pains, which come and go over a period of a few months. Others get periods of active AS (flare-ups), when symptoms become more severe and widespread. Other symptoms can include:

  • · loss of appetite
  • · general feeling of being unwell
  • · occasional inflammation of the eye (iritis)

When AS has been present for a few months, the back may stiffen, usually in the lower back. This happens when the inflammation reduces and healing takes place. Bone then grows out from both sides of the spine, joining the vertebrae together. Some people may stoop, whereas others develop a straight, stiff spine. In time, the inflammation can lead to permanent stiffness, but as the spine becomes more rigid, the pain may decrease. In some people the disease then disappears.

As the spine becomes more rigid, it is more prone to fractures (breaks).

If the joints where the ribs meet the spine are affected, breathing can become difficult and painful. However, only a minority of people who have ankylosing spondylitis develop a rigid spine and chest.


  • Doctors can often diagnose AS simply from a description of the symptoms and a physical examination.
  • Blood tests are performed to look for signs of inflammation. Blood may also be tested for HLA-B27. If this is present, it shows an increased risk of AS but does not prove the diagnosis.

X-rays are carried out to look for typical changes of AS, such as inflammation of the sacroiliac joints and damage to the joints in the spine.


The treatment of ankylosing spondylitis involves:

  • Medications to reduce inflammation and/or suppress immunity
  • Physical therapy
  • Exercise.

Medications decrease inflammation in the spine, and other joints and organs. Physical therapy and exercise help improve posture, spine mobility and lung capacity.