Ankylosing Spondylitis (ank-el-oh-sing spond-il-ite-is) (AS) is a type of progressive arthritis that leads to chronic inflammation of the spine and sacroiliac (sack-ro-ili-ack) (SI) joints. AS primarily affects the axial skeleton, including the ligaments and joints. Inflammation due to AS can also affect other joints and organs in the body, such as the eyes, lungs, kidneys, shoulders, knees, hips, heart, and ankles. AS is a true "systemic" disease, meaning the problem causes changes throughout the body.
One way to understand what AS does to the body is to look at the words "ankylosing" and "spondylitis." Ankylosing means stiffening. It comes from the Greek word "angkylos," which means bent. Spondylitis means inflammation of the spine. It comes from the Greek word "spondylos," which means spinal vertebrae. In essence, AS causes your spine to stiffen due to inflammation of the joints. This may cause the vertebrae to fuse together. It may also cause a kyphosis (kye-foh-sis) of the spine, which gives your spine a forward curve.
In its advanced stages, AS can be disabling, making it impossible to move.
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The origin of AS is still unknown. However, much is known about how AS progresses and why it causes spinal stiffening. When AS first appears, an inflammation of the bones (called osteitis [os-tee-ite-is]) occurs around the edges of the joints. In these areas, the number of special cells (called inflammatory cells) begins to increase. Inflammatory cells produce chemicals that damage the bone. This causes the bone to begin to dissolve and weaken around the edge of each joint.
As the bone becomes damaged, the body tries to repair the damage with scar tissue and new bone tissue. Eventually the bone becomes weaker and weaker. When the inflammation finally "burns out" and begins to disappear, the body attempts to heal the bone by depositing calcium around the area of the damage. For some unclear reason, as the bone heals itself, the calcium deposits spread to the ligaments and discs between the vertebrae. This causes the spine to fuse, which is sometimes called bony ankylosis.
AS primarily affects younger adult males. It is three times more common in males than females. Although AS can strike people of any age, race, or sex, the onset is most common in Caucasian men between the ages of 17 and 35. In women, the symptoms of AS often begin to appear during pregnancy.
AS appears to be genetic. A specific gene — the HLA-B27 gene — is present in 80% to 90% of people with AS. This does not mean that if you have the gene you will automatically get AS. About eight percent of Americans have the HLA-B27 gene, but only about one percent of those will actually develop AS.
The symptoms of AS are caused by the effects of inflammation. Initially the symptoms may come and go for weeks or months at a time.