How inflammation occurs and persists in different organs and joints in ankylosing spondylitis is a subject of active research. Each individual tends to have their own unique pattern of presentation and activity of the illness. The initial inflammation may be a result of an activation of the body's immune system, perhaps by a preceding bacterial infection or a combination of infectious microbes. Once activated, the body's immune system becomes unable to turn itself off, even though the initial bacterial infection may have long subsided. Chronic tissue inflammation resulting from the continued activation of the body's own immune system in the absence of active infection is the hallmark of an inflammatory autoimmune disease
People with ankylosing spondylitis can also have arthritis in joints other than the spine. This feature occurs more commonly in women. Patients may notice pain, stiffness, heat, swelling, warmth, and/or redness in joints such as the hips, knees, and ankles. Occasionally, the small joints of the toes can become inflamed or "sausage" shaped. Inflammation can occur in the cartilage around the breastbone (costochondritis) as well as in the tendons where the muscles attach to the bone (tendinitis) and in ligament attachments to bone. Some people with this disease develop Achilles tendinitis, causing pain and stiffness in the back of the heel, especially when pushing off with the foot while walking upstairs. Inflammation of the tissues of the bottom of the foot, plantar fasciitis, occurs more frequently in people with ankylosing spondylitis.
Other areas of the body affected by ankylosing spondylitis include the eyes, heart, and kidneys. Patients with ankylosing spondylitis can develop inflammation of the iris (iritis), the colored portion of the eye. Iritis is characterized by redness and pain in the eye, especially when looking at bright lights. Recurrent attacks of iritis can affect either eye. In addition to the iris, the ciliary body and choroid of the eye can become inflamed; this is referred to as uveitis. Iritis and uveitis can be serious complications of ankylosing spondylitis that can damage the eye and impair vision and may require an eye specialist's (ophthalmologist) urgent care. Special treatments for serious eye inflammation are discussed in the treatment section below. (It should be noted that iritis and inflammation of the spine can occur in other forms of arthritis such as reactive arthritis [formerly known as Reiter's syndrome], psoriatic arthritis, and the arthritis of inflammatory bowel disease.)
A rare complication of ankylosing spondylitis involves scarring of the heart's electrical system, causing an abnormally slow heart rate (referred to as heart block). A heart pacemaker may be necessary in these patients to maintain adequate heart rate and output. In others, the part of the aorta closest to the heart can become inflamed, resulting in leakage of the aortic valve. In this case, patients can develop shortness of breath, dizziness, andheart failure.
Advanced spondylitis can lead to deposits of protein material called amyloid into the kidneys and result in kidney failure.