What is Ankylosing Spondylitis?

Ankylosing spondylitis (AS) is a type of arthritis that causes inflammation (swelling) and pain in and around the spine, hip joints, chest wall, and places where ligaments and tendons join to bone. The name of this condition comes from the Greek words angkylos (bent) and spondylos (spinal vertebrae).¹

The exact cause of AS is not known, but it is considered to be an "autoimmune" disease — that is, a disease in which the immune system attacks other parts of the body. In this case, the immune system attacks the spine and causes the joints, tendons and ligaments to work less efficiently, usually beginning with inflammation where the spine meets the pelvis, in a place called the sacroiliac joint. For almost everyone, AS will cause a cycle of very painful periods of time (flares) followed by periods when the symptoms disappear (remission).^1,2,3

AS affects everyone differently, with some people having back pain and stiffness that comes and goes, while others suffer more severe pain that leads to varying degrees of spinal stiffness as the disease progresses. When the spine becomes more damaged by AS, the body makes repairs with tissue that slowly turns to bone. This can lead to the bones in the spine becoming fused or attached. If AS is not properly treated, it can be a very painful and debilitating condition. Some people will end up with a completely inflexible spine, like a single bone, leading to very limited movement of the back and neck.^1,2