Ankylosing spondylitis (pronounced ank-kih-low-sing spon-dill-eye-tiss), or AS, is a form of arthritis that primarily affects the spine, although other joints can become involved. It causes inflammation of the spinal joints (vertebrae) that can lead to severe, chronic pain and discomfort. In the most advanced cases (but not in all cases), this inflammation can lead to new bone formation on the spine, causing the spine to fuse in a fixed, immobile position, sometimes creating a forward-stooped posture. This forward curvature of the spine is called kyphosis. More information on kyphosis and fusion can be found in the Complications section.
AS can also cause inflammation, pain, and stiffness in other areas of the body such as the shoulders, hips, ribs, heels, and small joints of the hands and feet. Sometimes the eyes can become involved (known as iritis or uveitis,) and, rarely, the lungs and heart can be affected.
The hallmark feature of ankylosing spondylitis is the involvement of the sacroiliac (SI) joints during the progression of the disease. The SI joints are located at the base of the spine, where the spine joins the pelvis.
SAA receives no government funding and relies on the
generous donations from individuals to create and maintain the programs and
services aimed at improving the futures of the 2.7 million Americans affected
by spondylitis and its family of related diseases.
Currently, there is no known cure for AS, but there are treatments and medications available to reduce symptoms and manage pain. Recent studies show that the newer biologic medications can potentially slow disease progression in some people. Note that different people respond to different medications with varying levels of effectiveness. Thus, it may take time to find the most effective course of treatment.
Although the exact cause of AS is unknown, we do know that genetics play a key role in the disease. Most individuals who have AS also have a gene that produces a "genetic marker," a protein called HLA-B27. This marker is found in more than 95 percent of people in the Caucasian population with AS (the association between ankylosing spondylitis and HLA-B27 varies greatly between ethnic and racial groups; see the Diagnosis section for more information). It is important to note, however, that one does not have to be HLA-B27 positive to have AS. Also, a majority of people with this marker never develop ankylosing spondylitis.
Scientists suspect that other genes--along with a triggering environmental factor such as a bacterial infection, for example--are needed to activate AS in susceptible people. HLA-B27 likely accounts for about 30 percent of the overall risk, but there are numerous other genes working in concert with HLA-B27. Researchers have identified more than 60 genes that are associated with AS and related diseases. Among the newer key genes identified are ERAP 1, IL-12, IL-17, and IL-23.
One classic hypothesis has been that AS may start when the defenses of the intestines break down and certain bacteria pass into the bloodstream, triggering changes in the immune response.
The risk factors that predispose a person to AS include:
Unlike other forms of arthritis and rheumatic diseases, general onset of AS commonly occurs in younger people, between the ages of 17 and 45. However, it can also affect children and those who are much older.
The severity of AS varies greatly from person to person, and not everyone will experience the most serious complications or have spinal fusion. Some may experience only intermittent back pain and discomfort, while others may experience severe pain and stiffness over multiple areas of the body for long periods of time. AS can be debilitating and, in some cases, lead to disability.
Almost all cases of AS are characterized by acute, painful episodes (also known as "flares"), which are followed by temporary periods of remission when symptoms subside.
It is important to know that ankylosing spondylitis is a chronic, or lifelong, disease and that the severity of AS has nothing to do with age or gender. It can be just as severe in women and children as in men.
Remember that even if you have AS and are experiencing only mild symptoms, which you are able to manage well, it is important to see your rheumatologist once a year in order to detect and treat any underlying complications.
The Centers for Disease Control and Prevention's NHANES study now estimates that at least 2.7 million adults in the United States have axial spondyloarthritis.
Learn More About This Estimate
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