Your Health A-Z

Ankylosing spondylitis

Ankylosing spondylitis is a disorder that results in inflammation of the axial skeleton. The axial skeleton is the part of the skeleton that provides the main support for the body


  • Ankylosing spondylitis is a disease of unknown cause, which results in inflammation of certain joints, in particular the spine, sacro-iliac and hip joints.
  • The disease can also affect other peripheral joints, the eyes and the heart.
  • Ankylosing spondylitis is strongly associated with the presence in the body of an antigen called HLAB27.The main symptom of the disease is back pain with early morning stiffness, which is relieved by activity.
  • Treatment is through structured exercise and pain relief.
  • The disease is more common in men.

What is ankylosing spondylitis?

Ankylosing spondylitis is a disorder that results in inflammation of the axial skeleton. The axial skeleton is the part of the skeleton that provides the main support for the body, including the spine and pelvic joints. Other joints may also be involved – usually large joints of the arms and legs.

Ankylosing spondylitis can also affect the eyes and the heart through an immune process. These are known as extra-articular (occurring outside the joint) symptoms.

What causes ankylosing spondylitis?

The actual cause of the disease is not known. However, there is an association between ankylosing spondylitis and the presence of an antigen called HLA-B27. (An antigen is a substance regarded by the body as foreign or potentially dangerous against which it produces antibodies.) 

Ankylosing spondylitis occurs throughout the world in proportion to the presence of HLA-B27. In people of European descent, the prevalence of HLA-B27 is 7 percent and in people of African descent it is 4 percent. Of people with ankylosing spondylitis, over 90 percent are HLA-B27-positive. There is no relationship between disease severity and the presence of HLA-B27.

Who gets ankylosing spondylitis and who is at risk?

The disease usually begins between the ages of 20 and 40. It is about three times more common in men.

Ankylosing spondylitis is 10 times more common in first-degree relatives of someone with the disease.

The risk of developing ankylosing spondylitis if you are HLA-B27 positive is about 20%.

What are the symptoms and signs of ankylosing spondylitis?

The symptoms are usually noticed in the late teenage or early adult years. Onset after the age of 40 is unusual.

In most patients, the first symptom is dull pain, which starts slowly and gradually and is felt deep in the lower back or buttocks. This is usually accompanied by low-back morning stiffness, which lasts for a few hours and improves with activity. This stiffness may return with prolonged periods of inactivity.

Within a few months of onset, back pain becomes persistent and is generally worse at night. Some people even get up and walk around at night to alleviate it.

In some people, bony tenderness may accompany the back pain, while in others pain is the main complaint. Common sites of tenderness are the attachment of the ribs to the breastbone, along the spine, over the front of the pelvis, the top of the shins and the heels.

Arthritis of the hips and shoulders occurs at some stage in 25-35 percent of all patients. Arthritis of the peripheral joints other than the hips and shoulders is seen in 30 percent of patients and can occur at any stage of the disease.

Neck pain and stiffness are usually relatively late signs.

Some people with ankylosing spondylitis, usually those who develop the disease in their teens, may also complain of fever, fatigue, loss of appetite, weight loss or night sweats.

Ankylosing spondylitis may affect other organs too. A disorder of the eye, called acute anterior uveitis, is the most common. Attacks usually affect only one eye and can recur. The signs are pain and redness of the eye, difficulty coping with light (photophobia) and increased tearing of the eye (lacrimation).

A small number of patients develop problems with the aortic valve of the heart; this can occur early in the course of the disease.

The most specific things found on physical examination involve loss of mobility of the spine and limitation of chest expansion. Pain in the sacro-iliac joints of the pelvis may be reproduced when the doctor examines the patient either with direct pressure or with manoeuvres which stress the joints. There is often muscle spasm around the joints of the spine.

How is ankylosing spondylitis diagnosed?

The diagnosis of early ankylosing spondylitis before the development of irreversible deformity can be difficult.

Diagnosis generally depends on the presence of the following features:

  • a history of inflammatory back pain
  • limitation of motion of the lumbar spine in extension, flexion and bending from side to the side
  • limited chest expansion relative to standard values for age and sex
  • definite signs of inflamed sacro-iliac joints on an X-ray

These are known as the modified New York criteria and are used to make a diagnosis.

However, several studies have identified significant numbers of people who are positive for the HLA-B27 antigen and who have symptoms suggestive of ankylosing spondylitis, but show no changes on an X-ray. Most of these patients, when followed over time, eventually show X-ray changes.

Ankylosing spondylitis needs to be differentiated from other causes of low back pain and the following five features are used to do this:

  • age of onset below 40
  • a slow and gradual onset
  • pain present for more than three months before the patient sought medical attention
  • morning stiffness
  • improvement in the pain with exercise or activity

Can ankylosing spondylitis be prevented?

There is no known prevention of this disease.

How is ankylosing spondylitis treated?

There is no specific or definitive treatment for ankylosing spondylitis. The main goal of management is to engage the patient in a conscious programme of exercise designed to maintain a straight spine and preserve the full range of motion of any involved joints.

Many patients require anti-inflammatory medication to relieve the pain sufficiently to allow them to exercise.

Surgery is generally only used in patients with ankylosing spondylitis when they have severe arthritis of the hip joints. A small number of patients may benefit from surgical correction of extreme spinal deformities.

What is the outcome of ankylosing spondylitis?

The course of the disease is extremely variable, ranging from mild stiffness and evidence that the disease is confined to the sacro-iliac joints, to the other end of the spectrum:a totally fused spine (bamboo spine) and severe arthritis of both hips.

Pain tends to be persistent early in the disease and then becomes intermittent, with alternating exacerbations and quiet periods.

Onset of the disease in the teenage years correlates with both a worse outlook and more severe hip involvement.

The disease in women tends to be milder with less frequent progression to total spinal fusion (ankylosis). But it appears that women may suffer more from peripheral arthritis and may get late neck problems if they have the disease.

The most serious complication of the spinal disease is spinal fracture, which can occur with even minor trauma. Progressive lung problems are a rare complication of long-standing ankylosing spondylitis.

Heart valve problems and problems with the electrical conduction system of the heart increase with prolonged disease.

However, most patients with ankylosing spondylitis do not experience disabling symptoms and are able to lead a normal life.

When to call the doctor

  • If you have a family history of ankylosing spondylitis and have persistent back or joint pain.
  • If you have low back pain and a painful red eye.
  •  If you know you have the disease and experience a painful red eye, and/or an exacerbation of pain and stiffness.

Reviewed by Dr Pradeep Makan, orthopaedic surgeon, Melomed Gatesville and Life Vincent Pallotti Hospital in Cape Town and part-time lecturer in the department of orthopaedic surgery at the University of Cape Town, 2010.