What is ankylosing spondylitis?

Ankylosing spondylitis (say "AN-kill-ose-ing spon-dill-EYE-tis") is a form of arthritis that is long-lasting (chronic) and most often affects the spine. It can cause pain, stiffness, swelling, and limited motion in the low back, middle back, and neck, and sometimes areas such as the hips, chest wall, and heels. Ankylosing spondylitis is more common in men than women.

Although there is no cure, treatment can usually control symptoms and prevent the condition from getting worse. Most people are able to do normal daily activities and continue to work. Complications of ankylosing spondylitis may include inflammation of the colored part of the eye (iris), called iritis, or trouble breathing due to curving of the upper body and stiffening of the chest wall.

What causes ankylosing spondylitis?

The cause of ankylosing spondylitis is unknown, but a tendency to develop the condition may be genetic (passed down from parents to children). Most people with this condition are born with a particular gene, HLA-B27.¹ But having the HLA-B27 gene does not mean that you will develop ankylosing spondylitis. Current research suggests that both the environment and bacterial infections may also have roles in triggering ankylosing spondylitis.¹

What are the symptoms of ankylosing spondylitis?

Ankylosing spondylitis causes mild to severe back and buttock pain that is often worse in the early morning hours. This pain usually gets better with activity. It most often begins in the teens through the 30s and develops gradually.

In time, continued inflammation of the ligaments, tendons, joint capsules (soft tissues surrounding the joint), and joints of the spine will cause the spine to fuse together (ankylose), leading to less motion in the neck and low back. As the spine fuses, or stiffens, the neck and low back lose their normal curve, the mid-back curves outward (kyphosis), and a fixed bent-forward position can result, leading to significant disability. Inflammation of the small joints joining the ribs and collarbone to the breastbone can cause less expansion of the chest wall with breathing. The inflammation of ankylosing spondylitis can affect other parts of the body, most commonly other joints and the eyes, but sometimes the lungs, heart valves, and the major blood vessel called the aorta.

How is it diagnosed?

If your doctor suspects ankylosing spondylitis based on your history and symptoms, he or she can use a blood test for the HLA-B27 gene, an X-ray, or MRI of the sacroiliac joints to help make the diagnosis. The early signs of ankylosing spondylitis-dull low back and buttock pain and stiffness-are fairly common. If you have these symptoms for a period of time and they slowly increase, your doctor will ask about your pattern of symptoms and whether you have a family history of ankylosing spondylitis or similar joint disease.