Ankylosing Spondylitis
- IWBCA
- Feb 14
- 14 min read
Updated: Feb 18
Ankylosing spondylitis is a chronic inflammatory arthritis that primarily targets the spine and sacroiliac joints, causing inflammatory back pain, stiffness, and progressive loss of spinal mobility; it can also involve the hips, shoulders, eyes, skin, and gastrointestinal tract as part of a broader spondyloarthritis spectrum.
Overview
What is ankylosing spondylitis?
Ankylosing spondylitis is a form of inflammatory arthritis that mainly affects the axial skeleton, especially the joints in your spine and the sacroiliac joints, where the base of your spine meets your pelvis. Healthcare providers often classify it as axial spondyloarthritis, a term referring to inflammatory arthritis centered on the spine and sacroiliac joints.
The sacroiliac joints connect the sacrum, the triangular bone at the bottom of your spine, to the ilium, the upper and back part of your pelvis. These are among the largest weight-bearing joints in the body and are involved every time you walk, climb stairs, sit down, stand up, or shift your hips. In ankylosing spondylitis, these joints become chronically inflamed, which leads to pain, stiffness, and, over time, new bone formation that can reduce flexibility and fuse parts of the spine.
Although the spine and sacroiliac joints are the most common sites of disease, ankylosing spondylitis can also involve other large joints such as the hips, shoulders, and, less often, the knees. When these joints are affected, individuals may experience deep hip or shoulder pain, reduced range of motion, or difficulty with activities requiring bending, lifting, or reaching.
Ankylosing spondylitis is driven by inflammation, not simple “wear and tear.” Typical features include lower back pain and stiffness that are worse after rest or on waking and improve with movement, rather than pain that worsens with activity. In some people, it is part of a broader pattern of disease that includes gastrointestinal symptoms from inflammatory bowel disease, skin rashes such as psoriasis, eye inflammation such as acute anterior uveitis, fatigue, weight loss, or low-grade fevers.
Symptoms
What are the most common symptoms associated with ankylosing spondylitis?
Ankylosing spondylitis most often starts insidiously with back and hip symptoms that are easy to mistake for mechanical back strain. Over time, inflammation in the spine and sacroiliac joints can alter posture, limit flexibility, and cause pain in other joints and sites where tendons and ligaments insert into bone. Many people also experience fatigue and symptoms in other organs, such as the eyes, skin, and gastrointestinal tract.
Inflammatory Low Back Pain: Sacroiliitis is the hallmark of lower back pain. The pain is typically deep and aching rather than sharp, is worse first thing in the morning or after prolonged sitting, and improves with movement during the day. Many people notice night pain that wakes them in the second half of the night and eases when they get up and walk.
Pain That Radiates to Hips, Buttocks, and Spine: Back pain can radiate to the buttocks and hips, and sometimes to the back or sides of the thighs. Some people feel pain higher up in the spine or in the neck as inflammation gradually involves additional spinal levels. Deep buttock pain that alternates from one side to the other is especially suggestive of sacroiliac joint involvement.
Stiffness and Reduced Mobility: Stiffness in the lower back and hips, especially in the morning or after rest, is very common. People often describe feeling “locked up” on waking and needing time and movement to “loosen” their back. As ankylosing spondylitis progresses, forward bending, twisting, and looking over the shoulder may become more difficult, and posture may gradually change.
Pain and Stiffness in Other Joints: Although ankylosing spondylitis primarily affects the spine and sacroiliac joints, other large joints may also be involved. Hips and shoulders are most commonly affected, causing deep joint pain, reduced range of motion, and difficulty with walking, climbing stairs, dressing, or lifting. Knees, ankles, or other small joints may be involved in some people, typically more intermittently.
Enthesitis and Heel or Chest Wall Pain: Inflammation where tendons and ligaments attach to bone, called enthesitis, can cause focal pain at the heels, under the foot, along the back of the heel (Achilles tendon), around the kneecap, or at the front of the chest where the ribs meet the breastbone. Heel pain that is worse with the first steps in the morning and improves somewhat with movement is a common example.
Breathing Symptoms and Chest Tightness: Inflammation and stiffness of the joints between the ribs and spine can reduce chest wall expansion over time. Some people experience shortness of breath or chest tightness, particularly with exertion, not solely due to lung disease but because the chest cannot expand fully.
Fatigue and General Unwellness: Persistent fatigue is common and can be disproportionate to visible joint changes. Poor sleep from night pain, chronic inflammation, and the effort of coping with pain and stiffness all contribute. Some people notice low-grade fevers, a sense of “flu-like” malaise, or difficulty concentrating when the disease is active.
Weight Loss and Appetite Changes: Loss of appetite and unintentional weight loss can occur, particularly when inflammation is high or when ankylosing spondylitis is part of a broader inflammatory picture that includes the gut. These changes should always be discussed with a healthcare provider, especially if weight loss is rapid or unexplained.
Gastrointestinal Symptoms: Diarrhea, abdominal pain, or alternating bowel habits may indicate an association with inflammatory bowel disease in some individuals with ankylosing spondylitis. Even when full-blown inflammatory bowel disease is absent, milder gastrointestinal symptoms can occur within the spondyloarthritis spectrum and should be noted during evaluation.
Skin and Eye Manifestations: Skin rashes, including psoriasis, can coexist with ankylosing spondylitis in some individuals. Eye inflammation, such as acute anterior uveitis, can cause sudden eye pain, redness, light sensitivity, and blurred vision, and is an important extra-articular manifestation. Any new eye symptoms in someone with ankylosing spondylitis require urgent assessment.
Causes
What are the most common causes of ankylosing spondylitis?
Ankylosing spondylitis is an autoimmune, genetically influenced inflammatory disease. It occurs when the immune system mistakenly targets structures in and around the spine and sacroiliac joints, leading to chronic inflammation and new bone formation. Both inherited factors and environmental influences contribute; no single cause explains all cases.
Autoimmune and Autoinflammatory Immune Activity: In ankylosing spondylitis, parts of the immune system that normally defend against infections become inappropriately active against the body’s own tissues, particularly at entheses and in the sacroiliac joints and spine. This immune activity releases signaling molecules that drive chronic inflammation, pain, and eventual bony changes, including new bone formation and fusion.
Genetic Susceptibility and HLA-B27: Genetic factors are central. Many people with ankylosing spondylitis carry specific variants of immune genes, especially HLA-B27. HLA-B27 is a human leukocyte antigen that helps present protein fragments to immune cells. In certain forms, it appears to increase the likelihood of inappropriate immune activation. In some populations, more than 80 to 90 percent of people with ankylosing spondylitis have an HLA-B27 variant, and having an affected family member significantly increases risk.
Other Genetic Factors Beyond HLA-B27: HLA-B27 is not the only gene involved. Dozens of additional genes related to immune regulation, cytokine signaling, and barrier function in the gut and other tissues have been linked to ankylosing spondylitis. Each gene contributes a small amount, but together they shape the likelihood that someone with a susceptible background will develop the disease and the severity of the disease.
Family History and Shared Risk: Because multiple genes contribute, ankylosing spondylitis often clusters in families. A family history of ankylosing spondylitis, other spondyloarthritides, psoriasis, or inflammatory bowel disease increases the likelihood that back pain and stiffness reflect an underlying inflammatory disease rather than degenerative changes.
Environmental and Microbiome Triggers: Genetic susceptibility alone is not enough. Environmental factors, particularly the gut microbiome and, in some cases, prior infections, are thought to act as triggers in people who are already genetically at risk. Changes in the composition of gut bacteria or in immune responses to certain microbes may stimulate immune pathways that subsequently persist in the spine and sacroiliac joints.
Interaction of Genes, Immunity, and Lifestyle Factors: No single lifestyle factor “causes” ankylosing spondylitis; however, smoking, physical inactivity, and certain occupational demands can exacerbate symptoms or accelerate structural damage once disease is present. The core driver remains a genetically primed immune system interacting with environmental signals to produce chronic spinal and sacroiliac inflammation.
Understanding ankylosing spondylitis as an autoimmune, genetically influenced condition helps explain why one person with HLA-B27 may remain completely healthy while another develops progressive spinal arthritis, and why treatment focuses on calming the immune system rather than only masking pain.
Risk Factors
What are the most common risk factors associated with ankylosing spondylitis?
Anyone can develop ankylosing spondylitis, but certain characteristics and health patterns increase the likelihood that back pain and stiffness are due to this inflammatory disease rather than simple mechanical strain.
Younger Age: Ankylosing spondylitis typically begins in early adulthood. Most people are diagnosed before age 40, and a large proportion first notice symptoms around their late 20s or early 30s. Back pain that starts in this age range, especially when it behaves like inflammatory pain, is more concerning than new back pain that begins much later in life.
Male Sex: Ankylosing spondylitis affects people of all genders, but is diagnosed more often in males. Men tend to have more pronounced spinal changes on imaging and more classic axial symptom patterns, whereas women may have subtler imaging findings or more peripheral joint involvement, which can delay diagnosis.
Family History of Spondyloarthritis: Having a close biological relative with ankylosing spondylitis or another spondyloarthritis (e.g., psoriatic arthritis or inflammatory bowel disease–associated arthritis) significantly increases the risk of spondyloarthritis. A history of chronic back pain, “arthritis of the spine,” or unexplained uveitis in parents or siblings is a strong clue that a similar pattern in a younger family member may represent ankylosing spondylitis.
HLA-B27 Positivity: Carrying the HLA-B27 gene variant is one of the strongest known risk factors. Many individuals with ankylosing spondylitis are HLA-B27 positive, and the combination of HLA-B27 and inflammatory back pain makes the diagnosis more likely. At the same time, many people with HLA-B27 never develop the disease; thus, this gene increases risk but does not determine disease outcome in isolation.
Associated Immune-Mediated Conditions: Certain immune-mediated conditions cluster with ankylosing spondylitis. People with Crohn’s disease, ulcerative colitis, or psoriasis have a higher likelihood of developing axial spondyloarthritis. Recurrent anterior uveitis, dactylitis (“sausage digits”), and heel enthesitis are additional features that often share the same underlying immune pathways and should prompt evaluation for ankylosing spondylitis when present alongside back symptoms.
Smoking and Other Modifying Factors: Smoking does not cause ankylosing spondylitis by itself, but it is associated with more severe disease, faster radiographic progression, and worse functional outcomes in those who already have it. Physically demanding work, high-impact activities, or prolonged immobility can also exacerbate symptoms once the disease is established, even though they are not primary causes.
Complications
What are the most common complications associated with ankylosing spondylitis?
Without effective control, ankylosing spondylitis can change the structure and function of the spine, joints, and other organs over time. Complications arise from chronic inflammation, new bone formation, altered biomechanics, and associated immune and cardiovascular involvement.
Spinal Fractures: Inflammation and abnormal new bone formation can make the spine both stiff and fragile. The combination of reduced flexibility and underlying bone loss raises the risk of spinal fractures, sometimes from relatively minor trauma. Fractures of the rigid spine are often unstable and can compromise spinal cord function, making prevention and prompt recognition critical.
Fused Vertebrae and Spinal Rigidity: Progressive inflammation at the entheses and joints of the spine can lead to bony bridges between vertebrae. As vertebrae fuse, the spine loses its normal curves and the ability to flex or rotate. This fusion can lock the spine in a stooped or fixed position and significantly limit daily activities, including driving, lifting, and looking to the side.
Kyphosis and Postural Changes: Fusion and ligamentous ossification often produce an exaggerated forward curve in the thoracic spine (kyphosis). People may develop a forward-stooped posture, with difficulty standing fully upright or lifting the head to look straight ahead. This can strain neck muscles, alter balance, and increase the risk of falls.
Osteoporosis and Bone Fragility: Chronic inflammation, reduced mobility, and, in some cases, corticosteroid exposure contribute to decreased bone mineral density. Osteoporosis is more common in ankylosing spondylitis than in the general population and further increases the risk of vertebral and nonvertebral fractures.
Eye Inflammation and Vision Problems: Acute anterior uveitis is a well-recognized extra-articular complication. Flares cause eye pain, redness, light sensitivity, and blurred vision. Recurrent or inadequately treated uveitis can lead to complications such as cataracts, glaucoma, or macular edema; therefore, any new eye symptoms require urgent ophthalmologic evaluation.
Cardiovascular and Aortic Involvement: Ankylosing spondylitis can affect the heart and large vessels. Aortitis and aortic root dilation can lead to aortic valve insufficiency. Conduction system disturbances can cause arrhythmias or heart block. Over a lifetime, these changes contribute to an increased risk of cardiovascular morbidity, which makes routine cardiovascular risk assessment and management important.
Respiratory Restriction: Fusion of the costovertebral and sternocostal joints can limit chest wall expansion, thereby reducing lung volumes even when the lungs are otherwise healthy. People may notice breathlessness on exertion and have reduced tolerance for respiratory illness. Pulmonary apical fibrosis can develop in a subset of individuals with longstanding disease.
Nerve Involvement and Neurologic Complications: Spinal fractures, severe kyphosis, or spinal canal narrowing can compress nerve roots or, in rare cases, the spinal cord. This may cause radicular pain, numbness, weakness, or changes in coordination and balance. Atlantoaxial involvement in advanced disease can also pose neurologic risks and requires careful monitoring.
Functional Limitation and Psychosocial Impact: Chronic pain, stiffness, fatigue, and visible postural changes can limit work, recreation, and social activities. Over time, this may contribute to depression, anxiety, and reduced quality of life. Early diagnosis, effective control of inflammation, and ongoing physical therapy help reduce these burdens and maintain independence.
Diagnosis and Testing
How is ankylosing spondylitis diagnosed?
Diagnosis of ankylosing spondylitis relies on a combination of symptoms, physical examination, imaging findings, and selected laboratory tests. There is no single test that can confirm or exclude the condition. Clinicians look for a characteristic pattern of inflammatory back pain, reduced spinal mobility, and sacroiliac joint changes, while ruling out other causes of back pain and stiffness.
Initial Clinical Evaluation: A healthcare provider begins with a detailed history and physical examination. They ask when symptoms started, how long they last, whether back pain improves with movement or rest, and whether there is morning stiffness or night pain. They also ask about hip or shoulder pain, bowel symptoms, psoriasis, eye inflammation, and family history of spondyloarthritis. On examination, they assess spinal flexibility, chest expansion, posture, sacroiliac joint tenderness, and joint range of motion.
Referral to a Rheumatologist: If ankylosing spondylitis or axial spondyloarthritis is suspected, referral to a rheumatologist is often recommended. Rheumatologists specialize in inflammatory joint and spine disease and are best positioned to interpret subtle imaging changes, select appropriate blood tests, and apply formal classification criteria.
Imaging Studies: Imaging of the sacroiliac joints and spine is central to diagnosis. Plain X-rays of the sacroiliac joints can reveal characteristic changes, including erosions, subchondral sclerosis, joint space narrowing, and eventual ankylosis. These changes may take years to appear. Magnetic resonance imaging can detect earlier inflammatory changes, including bone marrow edema and active sacroiliitis, before structural damage is visible on X-ray. MRI is especially useful in younger patients with suggestive symptoms but normal radiographs.
Laboratory Tests: Blood tests support the diagnosis but do not define it. Testing for HLA-B27 helps identify a genetic susceptibility pattern; many individuals with ankylosing spondylitis are HLA-B27 positive, but some are not, and many HLA-B27–positive people never develop the disease. Inflammatory markers such as C-reactive protein and erythrocyte sedimentation rate may be elevated, although they can also be normal in active disease. Additional tests may be used to rule out other conditions, such as infections, rheumatoid arthritis, or metabolic bone disease.
Diagnostic Criteria and Exclusion of Other Causes: Formal classification frameworks combine clinical features, HLA-B27 status, and imaging findings to distinguish ankylosing spondylitis and axial spondyloarthritis from mechanical back pain and other illnesses. Diagnosing AS also requires excluding other explanations for symptoms, such as degenerative spine disease, spinal infection, malignancy, or inflammatory conditions with different patterns of joint involvement. A clear diagnosis guides appropriate treatment and long-term monitoring.
Management and Treatment
How is ankylosing spondylitis treated?
Treatment for ankylosing spondylitis focuses on controlling inflammation, relieving pain and stiffness, preserving spinal mobility and posture, and lowering the risk of long-term complications. Management typically combines structured exercise and physical therapy with medications tailored to the disease’s severity and pattern.
Treatment Goals: The main goals are to reduce pain, improve function, maintain the ability to work and perform daily activities, and prevent or delay structural damage in the spine and other affected joints. Because ankylosing spondylitis is chronic, treatment plans are designed for long-term use and are adjusted over time as needs change.
Exercise and Physical Therapy: Regular physical activity is a cornerstone of care. Movement reduces stiffness, helps maintain posture and spinal flexibility, and supports lung expansion. A physical therapist can design specific stretching and strengthening programs targeting the spine, hips, shoulders, and chest wall. Daily home exercises and attention to posture are often as important as medication in maintaining function.
Nonsteroidal Anti-Inflammatory Drugs: Nonsteroidal anti-inflammatory drugs such as ibuprofen and naproxen are commonly used as first-line medications. They reduce pain and stiffness by lowering inflammation in the spine and sacroiliac joints. Some individuals use these medications intermittently, whereas others require regular dosing. Long-term NSAID use requires monitoring for potential side effects, including stomach irritation, kidney effects, and cardiovascular risks.
Biologic Disease-Modifying Antirheumatic Drugs: Biologic DMARDs, particularly agents that block tumor necrosis factor alpha or interleukin-17 pathways, are used when symptoms remain active despite adequate trials of NSAIDs or when the disease is more severe. These medications can reduce inflammation, improve pain and function, and slow or prevent radiographic progression. They are prescription therapies given by injection or infusion and require regular follow-up and laboratory monitoring.
Other Medications and Local Corticosteroid Therapy: Local corticosteroid injections may be used for specific joints, such as the hip or shoulder, when focal inflammation does not respond to other measures. Systemic corticosteroids are not standard long-term therapy for axial disease but may be used briefly for certain extra-articular manifestations, such as severe uveitis, under specialist supervision.
Surgery and Interventional Options: Surgical intervention is uncommon but may be considered in selected situations. Hip replacement can be highly effective for advanced hip joint damage. Corrective spinal surgery is reserved for severe, fixed deformities that markedly interfere with function or vision. Decisions about surgery are made jointly by rheumatology, orthopedic surgery, and the patient after careful assessment of risks and benefits.
Self-Management and Lifestyle Measures: Stopping smoking, maintaining a healthy weight, optimizing bone health, and managing cardiovascular risk factors are all important. Attention to sleep, stress, and mental health can improve overall well-being and facilitate adherence to exercise and medication regimens. Regular follow-up with a rheumatologist enables ongoing therapy adjustments and early detection of complications.
Outlook and Prognosis
What can I expect if I have ankylosing spondylitis?
Ankylosing spondylitis is a lifelong condition, but its course is highly variable. Some individuals have mild disease with intermittent flares, while others develop more persistent symptoms and structural changes in the spine and hips. Modern therapies and early, consistent treatment have improved outcomes and reduced the likelihood of severe deformity for many people.
Long-Term Course and Symptom Patterns: AS typically follows a pattern of flares and periods of relative quiescence. Pain and stiffness may intensify for weeks or months and then subside, sometimes almost completely. Even during remission, inflammation can persist at low levels; therefore, regular follow-up is recommended. Over the years, some people develop increasing spinal rigidity, while others retain good flexibility and function.
Response to Treatment and Time to Improvement: Many people notice improvement within weeks of starting anti-inflammatory medications and structured exercise, although full benefit may take longer. Biologic therapies can lead to substantial symptom relief and improved function, but responses vary. Residual stiffness or fatigue is common even when pain is better controlled. Treatment plans are often adjusted over time to identify the combination that provides the optimal balance between benefits and adverse effects.
Impact on Daily Life and Work: With appropriate treatment, many individuals continue to work, care for family, and participate in preferred activities. Some may need to modify job tasks, adapt their work environment, or avoid repetitive heavy lifting. Early attention to posture, ergonomics, and regular movement during the day can reduce long-term strain on the spine.
Prognostic Factors and Complications: Risk of complications such as spinal fusion, kyphosis, osteoporosis, fractures, uveitis, and cardiovascular involvement varies. Factors associated with a more challenging course can include very early onset, high inflammatory markers, heavy smoking, and delayed diagnosis. Proactive management of bone health, cardiovascular risk, and eye symptoms helps reduce long-term impact.
Ankylosing Spondylitis Over Time: Although there is no cure, many people with ankylosing spondylitis lead full, active lives. Understanding the condition, staying engaged in care, reporting changes in symptoms, and working closely with a rheumatology team increase the likelihood that symptoms will remain manageable and that serious complications can be prevented or addressed early.
The IWBCA provides the information and materials on this site for educational and informational purposes only. The content is not a substitute for professional medical evaluation, diagnosis, or treatment. Always consult your physician or another qualified healthcare provider regarding any questions you may have about a medical condition, diagnosis, or course of treatment. Do not disregard, delay, or alter medical advice based on information obtained from this site. If you believe you are experiencing a medical emergency, call 911 or your local emergency services immediately.
Comments