The cause of ankylosing spondilitis is unknown, but genetic
factors seem to play a role. The disease starts with intermittent hip and/or lower-back
pain that is worse at night, in the morning, or after inactivity.
Back pain begins in the sacroiliac joint (between the pelvis and the spine) and may
progress to include the lumbosacral spine and the thoracic spine (chest portion of the
spine).
Pain may be eased by assuming a bent posture. Limited expansion of the chest occurs
because of the involvement of the joints between the ribs. The symptoms may worsen, go
into remission, or stop at any stage.
With progressive disease, deterioration of bone and cartilage can lead to fusion in the
spine or peripheral joints, affecting mobility. It can be extremely painful and crippling.
The heart, the lungs, and the eyes may also become affected.
The disease most frequently begins between age 20 and 40, but may begin before age 10.
It affects more males than females. Risk factors include a family history of ankylosing
spondylitis and male gender. About 0.21% of Americans over age 15 are affected.
Ankylosing spondylitis may be triggered by certain types of bacterial or viral
infections that activate an immune response that does not shut off after the infection is
healed. The immune system then attacks the body's own tissue. A disorder caused by the
body's own immune system is called an autoimmune disease.
Genetic markers are protein molecules found on the surfaces of cells. The HLA markers
enable the body's immune system to distinguish between "self" and
"other."
