Ankylosing spondylitis is a spondyloarthritis characterized by inflammation of the spine, large joints, and fingers and toes, resulting in stiffness and pain.
Prolonged joint pain, back stiffness, and eye inflammation are common.
The diagnosis is based on symptoms, x-rays, and established criteria.
Nonsteroidal anti-inflammatory drugs and sometimes sulfasalazine or methotrexate can help relieve the arthritis in limbs.
Secukinumab and drugs that inhibit tumor necrosis factor are very effective for spine and limb arthritis.
Ankylosing spondylitis is a type of spondyloarthritis.
Ankylosing spondylitis is 3 times more common among men than women, developing most commonly between the ages of 20 and 40. The cause of ankylosing spondylitis 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. The HLA-B27 gene is present in 90% of people who have ankylosing spondylitis, but it is also present in up to 10% of the general population depending on ethnicity. 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 may alternate with periods of almost no symptoms.
The most common symptom is
Back pain varies in intensity from one episode to another and from one person to another. Pain is often worse during the 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 painful but sometimes 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 What Is the Cauda Equina Syndrome?).
Lung disorders such as cough, coughing up blood (hemoptysis), and shortness of breath (dyspnea) can rarely develop.
The diagnosis of ankylosing spondylitis is based on the pattern of symptoms, a family history of the disorder, and on x-rays of the spine, pelvis, and affected joints. X-rays usually, but not always, 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). In some people, sacroiliitis is not visible on x-rays but may be detected by MRI of the pelvis or spine.
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; the level of C-reactive protein; and sometimes the presence of the HLA-B27 gene. High levels of ESR and C-reactive protein indicate inflammation but may not indicate the severity of the disorder. People may have the HLA-B27 gene and not have spondylitis.
Doctors can also base the diagnosis on an established set of criteria, but there are several different sets of criteria and some of them are undergoing changes. According to one set, people who have sacroiliitis confirmed by x-rays and one of the following may have ankylosing spondylitis:
Other criteria have been established to help diagnose people earlier. For example, the following criteria are sometimes applied to people who have had back pain for more than 3 months and who are under 45 years of age when their symptoms start. People who have sacroiliitis confirmed by x-rays or MRI and one of the following may have ankylosing spondylitis:
Dactylitis (swelling of an entire finger or toe)
Painful inflammation of the heel
Family history of spondyloarthritis
History of inflammatory back pain
Presence of the HLA-B27 gene
Eye inflammation (uveitis)
A high level of C-reactive protein
Relief of pain and inflammation with nonsteroidal anti-inflammatory drugs (NSAIDs)
People who have the HLA-B27 gene plus two of the criteria in the list above may also have ankylosing spondylitis.
Back pain due to inflammation 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 or longer before they see a doctor.
Treatment of ankylosing spondylitis is focused on
Nonsteroidal anti-inflammatory drugs (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 relieve the pain in joints other than those of the back. The tumor necrosis factor inhibitors etanercept, adalimumab, infliximab, golimumab, and certolizumab pegol effectively relieve back pain and inflammation. Secukinumab, an interleukin-17A receptor antagonist, can also reduce inflammation and joint symptoms.
The long-range goals of ankylosing spondylitis 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.
Corticosteroid eye drops 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.
Because chest wall motion can be restricted, which impairs lung function, cigarette smoking, which also impairs lung function, is strongly discouraged.
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