10 Facts About Ankylosing Spondylitis

Ankylosing spondylitis is pronounced ank-kih-low-sing spon-dill-eye-tiss. It is often referred to simply as AS. Ankylosis means “fusion” and spondylitis means “inflammation of the spine.” Here are the basic facts about this form of chronic autoimmune arthritis.

What is AS?

In autoimmune diseases, the immune system malfunctions and attacks healthy tissue. AS primarily affects the spine, causing inflammation of the vertebrae and spinal joints, such as the sacroiliac (SI) joint located where the spine connects to the pelvis. AS can also affect other joints in the body, as well as the eyes, and internal organs.


Genetics play a role in AS, particularly the HLA-B27 gene. Many people have this gene, but only 2 percent of those develop AS. The current theory is that an environmental trigger, e.g., a bacterial infection, starts the immune response leading to the development of AS in those who are susceptible.


AS typically develops between the ages of 15 and 30, although it can also happen at other ages. The first symptoms usually start in the sacroiliac joint. You may feel lower back pain that comes and goes, as well as pain and stiffness in the morning or after a period of inactivity. Other symptoms include pain and stiffness in other parts of the body, especially the Achilles tendon, the outside of the hips, and along the breastbone.


It can be difficult to diagnose AS and many people live with a mild form of the disease for years without knowing it. An in-depth discussion with your doctor about your symptoms, as well as a physical exam, testing inflammation markers in the blood (CRP and ESR), and imaging tests, can lead to a diagnosis.

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