What Is Ankylosing Spondylitis (AS)? Symptoms, Causes, Diagnosis, and Treatment
Ankylosing spondylitis is a form of chronic inflammatory arthritis that primarily affects the joints, ligaments, and tendons of the spine. Specifically, ankylosing spondylitis causes enthesitis — inflammation where the tendons, ligaments, and bones meet.
A hallmark of ankylosing spondylitis is inflammation of the sacroiliac joint, the joint between the sacrum, which is the bony structure at the base of the spine, and the bones of the pelvis.
In advanced cases, ankylosing spondylitis can cause new bone to grow in the inflamed areas and the vertebrae of the spine to fuse together.
This can lead to kyphosis, a type of spinal curvature that results in a forward-hunching posture.
People with ankylosing spondylitis may also have inflammation in other parts of their body, including the eyes — leading to a condition called uveitis.
Inflammation can additionally occur in the heel area as well as the knees, elbows, shoulders, and ribs.
The most common symptom of ankylosing spondylitis is low back pain that develops so gradually that it may go unnoticed in the early stages.
Other signs and symptoms of ankylosing spondylitis include:
Ankylosing spondylitis can also cause inflammation in other parts of the body, including the eyes, called uveitis, and the aortic valve and aorta, called aortitis.
Typically, symptoms worsen over time — gradually for some people and more rapidly for others.
Learn More About Signs and Symptoms of Ankylosing Spondylitis
People with ankylosing spondylitis often feel chronic pain, primarily in the spine, but sometimes also in other joints, including the:
Many people with AS have buttock pain, which is indicative of inflammation of the sacroiliac (SI) joints. The SI joints are located at the base of the spine, where the spine meets the pelvis.
The precise underlying cause of ankylosing spondylitis is unknown, but it is believed to have a strong genetic component, and possibly an environmental one.
Most individuals who have ankylosing spondylitis have a gene variation called HLA-B27.
Populations with a low frequency of the HLA-B27 gene variant have a correspondingly low occurrence of ankylosing spondylitis.
But most people with HLA-B27 do not develop ankylosing spondylitis, and it is not known how HLA-B27 increases AS risk.
Little is known about the environmental factors that trigger ankylosing spondylitis. Some researchers believe that bacterial infections may be a factor.
Whatever its trigger, ankylosing spondylitis is an “immune-mediated” disease, which means it results from abnormal activity of the body’s immune system. Immunologists disagree about whether it is an autoimmune disease.
In autoimmune diseases, the body mistakenly attacks a substance, called an antigen, that’s produced by the body. The blood proteins that attack the antigen are called autoantibodies, and they are detectable in a blood sample.
But research on the role of autoantibodies in ankylosing spondylitis is still evolving.
In recent years, scientists have begun to use the term “auto-inflammatory” to refer to inherited diseases that cause repeated episodes of inflammation in the absence of clear evidence of autoantibodies. In these diseases, it appears the immune system is reacting to something other than a self-antigen.
Because ankylosing spondylitis has some autoimmune characteristics and some auto-inflammatory characteristics, many experts believe it falls into both categories simultaneously.
There’s no single diagnostic test for ankylosing spondylitis. If your symptoms and medical history suggest you may have it, your doctor will likely do the following:
People with AS may be misdiagnosed with fibromyalgia, a chronic condition defined by pain and tenderness throughout the body that is often also associated with fatigue, anxiety, depression, sleep disturbances, and problems with memory or concentration.
But the pain of fibromyalgia is not associated with tissue inflammation the way AS pain is. Additionally, a key feature of fibromyalgia is that the pain and other symptoms are not explained by another rheumatic or systemic disorder.
Ankylosing spondylitis is a chronic disease that lasts a lifetime. But the effects of the disease and severity of symptoms vary from person to person. Some people have mild disease, with few symptoms, while others have chronic pain and stiffness that progress over time.
Effective treatment of ankylosing spondylitis can ease pain and stiffness, preserve physical functioning, and maximize quality of life. In some cases, treatment results in disease remission, meaning a person’s AS symptoms have little or no impact on their daily living, and their lab tests show low or no evidence of inflammation.
Ankylosing spondylitis is treated with a combination of medication and physical therapy.
The first drug your doctor prescribes will likely be a nonsteroidal anti-inflammatory drug (NSAID), such as naproxen (Aleve).
If an NSAID doesn’t provide enough relief, or if side effects become problematic, your doctor may prescribe a drug belonging to a category called tumor necrosis factor (TNF) alpha-blockers.
TNF alpha-blockers target the immune system and are used to treat rheumatoid arthritis and some other forms of inflammatory arthritis.
Other options include drugs called interleukin 17 (IL-17) inhibitors and Janus kinase (JAK) inhibitors. These drugs also target the immune system, but in different ways from TNF alpha-blockers. Because they dampen the immune system, taking these medicines may increase the risk of infection, heart complications, and some cancers.
Keeping physically active is key to living well with ankylosing spondylitis.
A physical therapist can teach you specialized exercises to encourage flexibility and strengthen your core so you can more easily maintain an upright posture when sitting and standing.
Your physical therapist may also be able to advise you on more comfortable sleeping positions.
Learn More About Treatment for Ankylosing Spondylitis: Medication, Exercise, and Surgery Options
Osteopenia and osteoporosis — both terms for low bone mass, or low bone mineral density — are common complications of ankylosing spondylitis, and both raise the risk of spinal fractures.
Other potential complications of ankylosing spondylitis include:
Some people with ankylosing spondylitis develop chronic inflammation at the base of the heart, around the aortic valve, and at the origin of the aorta, the main artery that carries blood away from the heart.
Years of chronic inflammation can lead to aortic regurgitation, a condition that occurs when the aortic valve doesn’t close properly, causing blood to flow backward.
In this particular study, aortic regurgitation was found in 18 percent of the participants with ankylosing spondylitis. In addition, aortic regurgitation was associated with both age and severity of ankylosing spondylitis.
The researchers suggested that routine care in ankylosing spondylitis should include monitoring with both echocardiography and electrocardiography. Once diagnosed, symptomatic aortic regurgitation can be treated with medication or by surgical repair or replacement.
Costochondritis is a condition that causes pain and tenderness in the chest. The pain happens in an area called the costosternal joints, where the ribs meet the breastbone.
Ankylosing spondylitis is a progressive disease. People with AS may initially have pain in the lower back, sacroiliac joints, or buttocks area that progresses to other areas, including the hips, shoulders, or neck.
Young to Middle Age Most people with ankylosing spondylitis have their first symptoms between the ages of 20 and 40, although about 10 to 20 percent have symptoms before age 18.
Race Ankylosing spondylitis occurs more frequently in white people, while African Americans usually have more severe disease.
Gender AS is more common in men than in women. Recent estimates suggest it occurs in 2 to 3 men for every woman with AS. There is some concern that women may be underdiagnosed because of different symptoms.
Genes Genetics appear to play a role in ankylosing spondylitis. Specifically, people who have a gene that produces a protein called HLA-B27 are at a significantly higher risk of being diagnosed, although only some with this gene actually get AS. Researchers believe that a combination of genetic and environmental factors are necessary to trigger ankylosing spondylitis. First-degree relatives (parents, siblings, and children) of an affected person have a higher risk than the general population.
Ankylosing spondylitis is one of a group of inflammatory rheumatic diseases known as spondylitis, spondyloarthropathy, or axial spondyloarthritis.
Other forms of spondylitis include nonradiographic axial spondylarthritis (nr-axSpA), a condition characterized by back pain and other symptoms but with no visible evidence of chronic inflammation on X-ray. In some cases, nr-axSpA later becomes ankylosing spondylitis.
Inflammatory back pain is another condition that causes back and buttock pain, similar to ankylosing spondylitis. It may or may not progress to another form of spondyloarthritis.
Decades ago, ankylosing spondylitis was treated with radiation to reduce inflammation in the spine. While the treatment had its desired effect, it also increased the risk of leukemia and aplastic anemia later in life.
While radiotherapy has since been replaced by drug therapy in the treatment of ankylosing spondylitis, researchers have continued to investigate whether modern treatments or the disease itself may be associated with a higher risk of cancer.
So far, study results have been mixed.
The best diet for people with ankylosing spondylitis is one that accomplishes the goals of maintaining a healthy weight, strong bones, and an active lifestyle.
A healthy weight is important to protect the joints and keep the immune system functioning well. Excess weight puts added stress on weight-bearing joints — primarily the knees, hips, and ankles, but also the lower back — and raises the risk of osteoarthritis in those joints.
Being underweight is associated with fatigue, anemia, osteoporosis, and a weakened immune system that cannot fight off illnesses effectively. Low body weight is also associated with infertility in women of childbearing age.
If you’re having trouble eating because of dental or digestive problems, have no appetite, or find you’re losing weight for no apparent reason, speak to your doctor.
Strong bones require adequate calcium and vitamin D. While calcium is relatively easy to get in food, vitamin D occurs naturally in only a few, including cold-water fish and egg yolks. To get enough, therefore, it may be necessary to consume foods fortified with vitamin D, such as milk and certain orange juices and cereals. Exposing your skin to sunlight is another way to raise your vitamin D level.
RELATED: 10 Vitamin D-Rich Foods to Add to Your Diet
Consuming too much alcohol also weakens the bones, so if you wish to drink, talk to your doctor about a safe amount.
Arthritis Foundation: Ankylosing Spondylitis and Nonradiographic Axial Spondyloarthritis
CreakyJoints: 12 Ankylosing Spondylitis Symptoms You Can’t Afford to Ignore
Cleveland Clinic: Strategies for Coping With Ankylosing Spondylitis
Spondylitis Association of America: Medications Used to Treat Ankylosing Spondylitis and Related Diseases
Arthritis National Research Foundation: Clinical Trials
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