Ankylosing spondylitis is a spondyloarthritis characterized by inflammation of the spine, large joints, and fingers and toes, resulting in stiffness and pain.
Ankylosing spondylitis is a type of spondyloarthritis (see Spondyloarthritis).
Ankylosing spondylitis is 3 times more common among men than women, developing most commonly between the ages of 20 and 40. Its cause is not known, but the disease tends to run in families, indicating that genetics plays a role. Ankylosing spondylitis is 10 to 20 times more common among people whose parents or siblings have it. However, only 50% of identical twins both have the disorder, which suggests that unknown environmental factors also may be involved.
Mild to moderate flare-ups of inflammation generally alternate with periods of almost no symptoms.
The most common symptom is back pain, which varies in intensity from one episode to another and from one person to another. Pain is often worse at night and in the morning. Early morning stiffness that is relieved by activity is also very common. Pain in the lower back and the associated muscle spasms are often relieved by bending forward. Therefore, people often assume a stooped posture, which can lead to a permanent bent-over position. In others, the spine becomes noticeably straight and stiff.
Loss of appetite, low-grade fever, weight loss, excessive fatigue, and anemia can accompany the back pain. If the joints connecting the ribs to the spine are inflamed, the pain may limit the ability to expand the chest to take a deep breath. Stiffness (fusion) of the spine can restrict the ability to expand the chest wall as well. Occasionally, pain starts in large joints, such as the hips, knees, and shoulders.
One third of the people have recurring attacks of mild eye inflammation (uveitis), which usually does not impair vision if treated promptly. In a few people, inflammation of a heart valve results in a permanently damaged valve, or other problems can affect the heart or aorta. If damaged vertebrae press against nerves or the spinal cord, numbness, weakness, or pain can develop in the area supplied by the affected nerves. Cauda equina (horse's tail) syndrome is an occasional complication (see see Sidebar 4: What Is the Cauda Equina Syndrome?). Lung disorders such as cough, coughing up blood (hemoptysis), and shortness of breath (dyspnea) can rarely develop. Achilles and patellar tendinitis can develop.
The diagnosis is based on the pattern of symptoms, a family history of the disorder, and on x-rays of the spine and affected joints. X-rays show a wearing away (erosion) of the joint between the spine and the hip bone (sacroiliac joint) and the formation of bony bridges between the vertebrae, making the spine stiff (sacroiliitis). Blood tests are done to determine the erythrocyte sedimentation rate (ESR), a test that measures the rate at which red blood cells settle to the bottom of a test tube containing blood, and the level of C-reactive protein. High levels indicate inflammation.
Doctors can also base the diagnosis on an established set of criteria. People who have sacroiliitis and one of the following are diagnosed with ankylosing spondylitis:
Inflammatory back pain usually begins gradually when a person is 40 or younger. People have stiffness in the morning that is relieved by movement.
People typically have symptoms for about 3 months before they see a doctor.
Most people develop some disabilities but can still lead normal, productive lives. In some people, the disease is more progressive, causing severe deformities. The prognosis is discouraging for people who develop extreme stiffness of the spine.
Treatment focuses on relieving back and joint pain, maintaining range of motion in the joints, preventing damage in other organs, and preventing or correcting spinal deformities. NSAIDs can reduce pain and inflammation, thus enabling people to do important exercises to retain posture, including stretching and deep breathing. In some people, sulfasalazine or methotrexate may help the pain in joints other than those of the back. The TNF inhibitors etanercept, adalimumab, or infliximab effectively relieve back pain and inflammation.
Corticosteroid and dilating eye drops may help in the short-term treatment of inflammation of the eyes, and an occasional corticosteroid injection may be helpful for 1 or 2 joints other than the spine. Muscle relaxants and opioid analgesics are occasionally used, but for only brief periods to relieve severe pain and muscle spasms. If the hips become eroded or fixed in a bent position, surgical treatment to replace the joint can relieve pain and restore function.
The long-range goals of treatment are to maintain proper posture and develop strong back muscles. Daily exercises strengthen the muscles that oppose the tendency to bend and stoop. It has been suggested that people spend some time each day—often while reading—lying on their stomach propped up on their elbows because this position extends the back and helps to keep the back flexible. Because chest wall motion can be restricted, which impairs lung function, cigarette smoking, which also impairs lung function, is strongly discouraged.
Last full review/revision May 2013 by Roy D. Altman, MD