Ankylosing spondylitis, also known as axial spondyloarthritis, is an inflammatory disease that, over time, can cause some of the bones in the spine, called vertebrae, to fuse. This fusing makes the spine less flexible and can result in a hunched posture. If ribs are affected, it can be difficult to breathe deeply.
Axial spondyloarthritis has two types. When the condition is found on X-ray, it is called ankylosing spondylitis, also known as axial spondyloarthritis. When the condition can't be seen on X-ray but is found based on symptoms, blood tests and other imaging tests, it is called nonradiographic axial spondyloarthritis.
Symptoms typically begin in early adulthood. Inflammation also can occur in other parts of the body — most commonly, the eyes.
There is no cure for ankylosing spondylitis, but treatments can lessen symptoms and possibly slow progression of the disease.
Early symptoms of ankylosing spondylitis might include back pain and stiffness in the lower back and hips, especially in the morning and after periods of inactivity. Neck pain and fatigue also are common. Over time, symptoms might worsen, improve or stop at irregular intervals.
The areas most commonly affected are:
- The joint between the base of the spine and the pelvis.
- The vertebrae in the lower back.
- The places where tendons and ligaments attach to bones, mainly in the spine, but sometimes along the back of the heel.
- The cartilage between the breastbone and the ribs.
- The hip and shoulder joints.
When to see a doctor
Seek medical attention if you have low back or buttock pain that came on slowly, is worse in the morning or awakens you from your sleep in the second half of the night — particularly if this pain improves with exercise and worsens with rest. See an eye specialist immediately if you develop a painful red eye, severe light sensitivity or blurred vision.
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 a greatly increased risk of developing ankylosing spondylitis. However, only some people with the gene develop the condition.
Onset generally occurs in late adolescence or early adulthood. Most people who have ankylosing spondylitis have the HLA-B27 gene. But many people who have this gene never develop ankylosing spondylitis.
In severe ankylosing spondylitis, new bone forms as part of the body's attempt to heal. This new bone gradually bridges the gap between vertebrae and eventually fuses sections of vertebrae. Those parts of the spine become stiff and inflexible. Fusion also can stiffen the rib cage, restricting lung capacity and function.
Other complications might include:
- Eye inflammation, called uveitis. One of the most common complications of ankylosing spondylitis, uveitis can cause rapid-onset eye pain, sensitivity to light and blurred vision. See your health care provider right away if you develop these symptoms.
- Compression fractures. Some people's bones weaken during the early stages of ankylosing spondylitis. Weakened vertebrae can crumple, increasing the severity of a stooped posture. Vertebral fractures can put pressure on and possibly injure the spinal cord and the nerves that pass through the spine.
- Heart problems. Ankylosing spondylitis can cause problems with the aorta, the largest artery in the body. The inflamed aorta can enlarge to the point that it distorts the shape of the aortic valve in the heart, which impairs its function. The inflammation associated with ankylosing spondylitis increases the risk of heart disease in general.