Ankylosing spondylitis is a type of arthritis of the spine.
It causes swelling between your vertebrae, which are the disks that make up your spine, and in the joints between your spine and pelvis. Ankylosing spondylitis is an immune disease. The disease is more common and more severe in men. It often runs in families.
Early symptoms include back pain and stiffness. These problems often start in late adolescence or early adulthood. Over time, ankylosing spondylitis can fuse your vertebrae together, limiting movement. Symptoms can worsen or improve or stop altogether. The disease has no cure, but medicines can relieve the pain, swelling and other symptoms. Exercise can also help.
Source: National Institute of Arthritis and Musculoskeletal and Skin Disease