Ankylosing spondylitis: A form of chronic inflammation of the spine and the sacroiliac joints. Chronic inflammation in these areas causes pain and stiffness in and around the spine. Over time, chronic spinal inflammation (spondylitis) can lead to a complete cementing together (fusion) of the vertebrae, a process called ankylosis. Ankylosing spondylitis can sometimes be seen in patients with psoriasis and inflammatory bowel disease (ulcerative and Crohn's colitis).
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