Ankylosing spondylitis is a progressive inflammatory disease that typically becomes evident during early to mid adulthood. The disease is characterized by inflammation (arthritis), stiffness, and pain of various joints of the spine and potential loss of spinal mobility. It may involve joints between the spine and the pelvis, known as the sacroiliac joints; joints within the spinal column of the lower back (lumbar spine), the upper back (thoracic spine), and the neck (cervical spine) to varying degrees; as well as joints of the limbs, particularly the legs. Progression may spontaneously subside at any stage of involvement; however, in some individuals, all regions of the spinal column may eventually become involved.
Many affected individuals develop lower back and hip pain that may be more severe at night and after rest. In addition, there is often associated stiffness of affected regions in the morning. In some cases, those with involvement of joints joining the ribs with the spine (costovertebral joints) may have a limited ability to expand the chest to take a deep breath. In addition, in some affected individuals, other associated findings may include recurrent inflammation of the colored region of the eyes (acute iritis), leakage of the aortic valve resulting in a backflow of blood into the lower left chamber (ventricle) of the heart (aortic insufficiency or regurgitation), and/or other abnormalities.
The exact cause of ankylosing spondylitis is not known. However, researchers suggest that genetic, immunologic, and/or environmental factors may play some role.