This condition does not meet the definition of a rare disease in the U.S. (fewer than 200,000 Americans). There may be forms of this condition that are rare. NORD posts this report because limited information is available about this condition and it may be underdiagnosed.
Última actualización:
11/20/2025
Años publicados: 1986, 1987, 1988, 1991, 1994, 1997, 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2025
NORD gratefully acknowledges Gioconda Alyea, MD (FMG), MS, National Organization for Rare Disorders, for assistance in the preparation of this report.
Summary
Ankylosing spondylitis (AS) is a chronic (long-term) inflammatory condition that primarily affects the joints that connect the base of the spine to the pelvis (the sacroiliac joints). The condition typically begins in young adulthood and is marked by persistent back pain and stiffness that gradually worsens over time. As the condition progresses, it can lead to reduced spinal mobility, changes in posture, and, in some cases, the bones of the spine may even fuse together (fusion of the spinal vertebrae).
AS does not only affect the joints within the spinal column of the lower back (lumbar spine). It can also affect the upper back (thoracic spine), neck (cervical spine) and sometimes joints in the arms or legs – especially the hips. Many affected people develop lower back and hip pain that may be more severe at night and after rest. In addition, there is often associated stiffness in affected regions in the morning. In some cases, if the joints where the ribs meet the spine (costovertebral joints) become inflamed, it can make it harder to expand the chest to take a deep breath.
Other associated findings may include recurrent (frequent) inflammation of the colored region of the eyes (acute iritis), which causes redness, pain, and/or sensitivity to light. In some cases, AS can affect the heart through leakage of the aortic valve resulting in a backflow of blood into the lower left chamber (ventricle) of the heart (aortic insufficiency or regurgitation), and/or other abnormalities.
The exact cause of AS is not known. However, researchers suggest that genetics, the immune system (immunology), and/or environmental factors may play some role.
Though AS is a lifelong condition, treatment can significantly reduce symptoms and help people with AS maintain a good quality of life.
Ankylosing spondylitis (AS) is in a family of disorders called spondyloarthritis (SpA). Early descriptions of the condition date back to ancient times. Galen provided the earliest accounts, but it was not until the 19th century that reports from Pierre Marie, Adolph Strümpell, and Vladimir Bekhterev allowed for a precise diagnosis of the illness.
The most common symptom of AS is chronic back pain, which often starts before 40 years of age and develops gradually. Unlike typical back pain, the pain associated with AS tends to improve with physical activity and worsen during periods of rest. Many people also report stiffness in the back, particularly in the morning or after being inactive for a while. As the disease progresses, movement in the spine may become more limited.
Other signs and symptoms may include:
In addition to these musculoskeletal symptoms, people with AS may have Inflammation in other parts of the body:
The exact cause of ankylosing spondylitis (AS) is still not known, but research suggests that both genetic and the immune system play important roles in the development of the disease.
One of the strongest known risk factors is a gene called HLA-B27. About 80-95% of people with AS have this gene. However, not everyone who carries HLA-B27 will develop AS. In fact, many people with this gene never experience any symptoms. Still, having HLA-B27 increases the likelihood of developing AS, especially when combined with other factors. The gene appears to affect how the immune system responds to certain triggers, which may lead to long-term inflammation in the joints and other tissues.
In addition to the HLA-B27 gene, researchers have found 113 other genetic factors that may play a role in ankylosing spondylitis (AS). Some of the newer genes identified are ERAP 1, IL-12, IL-17, and IL-23. These genes together help explain about 10% of the chances that someone might inherit AS from their family. This means AS is influenced by many genes plus other factors.
HLAs (human leukocyte antigens) are proteins that help the immune system recognize what belongs in the body and what doesn’t. The cluster of genes that determine and regulate production of such proteins is called the major histocompatibility complex (MHC). The MHC has been mapped to a region on the short arm (p) of chromosome 6 (The region is called 6p21.3.). Researchers suggest that certain genes on other chromosomes may also possibly be a factor in genetically predisposing to ankylosing spondylitis in some cases.
Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Humans have 23 pair of chromosomes. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as “p” and a long arm identified by the letter “q.” Chromosomes are further subdivided into bands that are numbered. Therefore, for example, 6p21.3 refers to band 21.3 on the short arm of chromosome 6.
Scientists believe that AS may be triggered when a person with the right genetic background (a genetically susceptible person) is exposed to certain environmental or microbial factors, such as infections, that activate the immune system abnormally. Once triggered, the immune system may mistakenly attack the body’s own joints, particularly where tendons and ligaments attach to bone, causing ongoing inflammation.
It is also possible that gut health plays a role in some cases. There is growing evidence that certain bacteria in the digestive system may influence immune activity in people with AS, particularly in those who also have inflammatory bowel disease. However, no single bacteria or environmental factor has been definitively proven to cause AS.
Estimates of how many Americans have ankylosing spondylitis (AS) vary widely. Some sources suggest at least 1.7 million adults have AS, while others report close to 3 million Americans have it. Another source estimates that around 300,000 Americans have AS, although this is less than one percent of the adult population. The higher numbers likely include cases of axial spondyloarthritis (axSpA), which is a broader category that includes AS.
AS usually develops in individuals under the age of 40, and most patients notice symptoms in their late teens to early thirties. The condition is more common in men than in women and often runs in families. Among individuals who are HLA-B27 positive, the prevalence of AS is approximately 5% to 20%. In the United States, the prevalence of HLA-B27 varies among ethnic groups.
Diagnosing AS usually involves several steps: a detailed medical history, a physical examination, imaging tests, and blood work.
Doctors often suspect AS when a person has inflammatory back pain – pain that improves with activity, does not get better with rest, and may be worse at night.
Imaging tests of the sacroiliac joints (where the spine meets the pelvis) and spine are very important in confirming the diagnosis. X-rays may reveal changes such as joint erosion (loss of bone), sclerosis (bone thickening), and in advanced cases, fusion of the spine that can look like a “bamboo spine.” Magnetic resonance imaging (MRI) can detect inflammation in the early stages before changes become visible on X-ray. This can help diagnose AS in its early stages.
Blood tests may show elevated markers of inflammation, such as erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP). However, some people with AS have normal blood tests. Doctors may also check for the HLA-B27 gene, which increases the likelihood of AS but does not confirm it on its own.
Treatment
The primary goals of treatment are to relieve pain and stiffness, preserve spinal mobility (keep the spine flexible), maintain daily function, and prevent complications. A combination of medication and physical therapy is usually recommended.
People affected by AS usually need to be seen and followed by several specialists, who should work together as a team in a coordinated way, for the best management. A rheumatologist (a doctor who specializes in arthritis and autoimmune diseases) typically oversees treatment and monitoring. Depending on the patient’s specific symptoms, other healthcare providers may be involved, including ophthalmologists for eye inflammation, gastroenterologists for inflammatory bowel disease, dermatologists for skin involvement, and physical therapists for movement and rehabilitation support.
Non-steroidal anti-inflammatory drugs (NSAIDs) are typically the first line of treatment and are often effective in reducing pain and inflammation. If NSAIDs do not control symptoms, biologic medications may be introduced, particularly tumor necrosis factor inhibitors (TNF inhibitors) such as adalimumab, infliximab, or etanercept. These biologic agents have been shown to significantly reduce inflammation and slow disease progression. Treatment response is generally assessed after several weeks because it can take several weeks to see results.
Systemic corticosteroids are generally not used to treat AS but may be considered in the form of localized injections for specific areas of inflammation.
The Spondylitis Association of America keeps an updated list of medications used in ankylosing spondylitis.
It is also important for affected people to engage in regular exercise, as physical activity is one of the most effective non-drug therapies for AS. Physical therapy can help maintain posture, flexibility, and chest expansion.
Exercises may be prescribed under a doctor’s supervision stressing back movements, deep breathing, straightening of the chest portion of the spine, deep-bending exercises, and a full range of motion of the spine in all directions. Bending (flexion) postures should not be maintained for long periods of time. To avoid flexion of the neck and upper back, affected individuals should sleep on their backs with a firm mattress and use no pillow or a very flat pillow. The chest muscles can be stretched and the upper back straightened by locking the fingers behind the head and pushing the elbows as far back as possible.
Water-based exercises and structured rehabilitation programs have been shown to improve function and reduce symptoms. Swimming is also excellent exercise for people with this disorder. Prior to exercise, hot baths or warm showers may be helpful to relax muscles and to attain better range of motion.
These exercises and physical therapy can be administered immediately upon diagnosis to retain as normal an upright posture as possible and reduce the potential for physical deformity. This is particularly important for people who are diagnosed early in life.
People with AS should have ample rest each day and avoid exhaustion, but long periods of inactivity can make symptoms worse.
Smoking cessation is strongly encouraged, especially given the potential impact of AS on lung function.
Sometimes, people with AS need surgery to help with pain or movement problems. The different surgeries may include:
With appropriate treatment, most people with AS are able to maintain their independence and continue participating in daily activities. Severe disability is relatively uncommon. Long-term complications can include increased risk of cardiovascular disease and, in rare cases, nerve compression syndromes such as cauda equina syndrome (a medical emergency that happens when an injury or herniated disk compresses nerve roots at the bottom of your spinal cord).
Potential complications of AS include chronic pain, decreased spinal mobility, spinal fractures, heart valve problems, lung fibrosis (a disease that causes scarring of the lung tissue, making it stiff and less able to transfer oxygen to the blood), and, occasionally, mood disorders related to chronic illness. These complications can significantly impact quality of life if not identified and managed early.
Patients should understand that AS is a chronic, manageable condition that requires long-term care. Being informed about the disease and actively participating in treatment decisions can improve outcomes. Patients should be aware of the benefits and potential side effects of medications, understand the importance of regular physical activity, and seek support when needed. Early engagement in treatment and routine follow-up with healthcare providers can help prevent complications and maintain functionality.
References
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JOURNAL ARTICLES
Proft F, Poddubnyy D. Ankylosing spondylitis and axial spondyloarthritis: recent insights and impact of new classification criteria. Ther Adv Musculoskelet Dis. 2018;10(5-6):129-139. doi:10.1177/1759720X18773726
Bridgewood C, Watad A, Cuthbert RJ, McGonagle D. Spondyloarthritis: new insights into clinical aspects, translational immunology and therapeutics. Curr Opin Rheumatol. 2018;30(5):526-532. doi:10.1097/BOR.0000000000000529
Watad A, Cuthbert RJ, Amital H, McGonagle D. Enthesitis: Much More Than Focal Insertion Point Inflammation. Curr Rheumatol Rep. 2018;20(7):41. Published 2018 May 30. doi:10.1007/s11926-018-0751-3
Kucybała I, Urbanik A, Wojciechowski W. Radiologic approach to axial spondyloarthritis: where are we now and where are we heading?. Rheumatol Int. 2018;38(10):1753-1762. doi:10.1007/s00296-018-4130-1
Agrawal P, Tote S, Sapkale B. Diagnosis and Treatment of Ankylosing Spondylitis. Cureus. 2024;16(1):e52559. Published 2024 Jan 19. doi:10.7759/cureus.52559
Kivitz AJ, Wagner U, Dokoupilova E, et al. Efficacy and Safety of Secukinumab 150 mg with and Without Loading Regimen in Ankylosing Spondylitis: 104-week Results from MEASURE 4 Study. Rheumatol Ther. 2018;5(2):447-462. doi:10.1007/s40744-018-0123-5
Curtis JR, Winthrop K, Bohn RL, et al. The Annual Diagnostic Prevalence of Ankylosing Spondylitis and Axial Spondyloarthritis in the United States Using Medicare and MarketScan Databases. ACR Open Rheumatol. 2021;3(11):743-752. doi:10.1002/acr2.11316
Hanson A, Brown MA. Genetics and the Causes of Ankylosing Spondylitis. Rheum Dis Clin North Am. 2017;43(3):401-414. doi:10.1016/j.rdc.2017.04.006
Braun WE. HLA molecules in autoimmune diseases. Clin Biochem. 1992;25:187-91.
Moreland LW, et al. Infection as a cause of reactive arthritis, ankylosing spondylitis, and rheumatic fever. Curr Opin Rheumatol. 1992;4:534-42.
Buxbaum J. Therapy for the seronegative spondyloarthropathies. Curr Opin Rheumatol. 1992;4:500-6.
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FROM THE INTERNET
Brent LH. Ankylosing Spondylitis and Undifferentiated Spondyloarthropathy Treatment & Management. Medscape Reference. October 16, 2024. Available at: https://emedicine.medscape.com/article/332945-treatment Accessed on 11/6/2025.
Tubergen AV. Treatment of axial spondyloarthritis (ankylosing spondylitis and nonradiographic axial spondyloarthritis) in adults. UpToDate. May 05, 2025. Available at: https://www.uptodate.com/contents/treatment-of-axial-spondyloarthritis-ankylosing-spondylitis-and-nonradiographic-axial-spondyloarthritis-in-adults Accessed on 11/6/2025.
Wenker KJ, Quint JM. Ankylosing Spondylitis. [Updated 2023 Jun 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470173/
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