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Ankylosing spondylitis
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Ankylosing spondylitis

Ankylosing spondylitis is a chronic inflammatory arthritis primarily affecting the spine, causing progressive pain, stiffness, and eventual fusion of vertebrae, with symptoms typically beginning between ages 15 and 30.

Overview

Ankylosing spondylitis is a form of painful, ongoing joint inflammation (chronic inflammatory arthritis) that primarily affects the spine. Early symptoms of ankylosing spondylitis typically begin between the ages of 15 and 30. Most commonly, affected individuals first experience chronic back pain and stiffness. This pain worsens with rest or inactivity, and tends to be relieved with physical activity or exercise.

Pain in ankylosing spondylitis results from inflammation of the joints between the pelvic bones (the ilia) and the base of the spine (the sacrum). These joints are called sacroiliac joints, and inflammation of these joints is known as sacroiliitis. The inflammation gradually spreads to the joints between the vertebrae, eventually involving the whole spine, causing a condition called spondylitis. Over time, back movement gradually becomes limited as the bones of the spine (vertebrae) fuse together. This progressive bony fusion is called ankylosis. These fused bones are prone to fracture.

Ankylosing spondylitis can involve other joints as well, including the shoulders, hips, and, less often, the knees. As the disease progresses, it can affect the joints between the spine and ribs, restricting movement of the chest and making it difficult to breathe deeply.

Ankylosing spondylitis affects the eyes in more than 30 percent of cases, leading to episodes of eye inflammation called acute iritis. Acute iritis typically affects one eye at a time and causes eye pain and increased sensitivity to light (photophobia). Rarely, ankylosing spondylitis can also cause serious complications involving the heart, lungs, and nervous system. Six to 10 percent of people with ankylosing spondylitis have additional inflammatory disorders such as psoriasis, which affects the skin, or ulcerative colitis or Crohn's disease, which both affect the digestive tract.

Frequency

Ankylosing spondylitis is part of a group of related diseases known as spondyloarthritis. In the United States, spondyloarthritis affect 3.5 to 13 per 1,000 people. Ankylosing spondylitis appears to be more common in certain indigenous populations in North America, Europe, and Asia.

Causes & Risk Factors

Ankylosing spondylitis is likely caused by a combination of genetic and environmental factors, most of which have not been identified. However, researchers have found variations in several genes that influence the risk of developing this disorder.

The HLA-B gene provides instructions for making a protein that plays an important role in the immune system. The HLA-B gene is part of a family of genes called the major histocompatibility complex (MHC). The HLA complex helps the immune system distinguish the body's own proteins from proteins made by foreign invaders (such as viruses and bacteria). The HLA-B gene has many different normal variations, allowing each person's immune system to react to a wide range of foreign proteins. A normal variant of the HLA-B gene called HLA-B27 significantly increases the risk of developing ankylosing spondylitis. Although some people with ankylosing spondylitis have the HLA-B27 variant, most people with this version of the HLA-B gene never develop the disorder. (Conversely, this condition can occur in people without the HLA-B27 gene variant.) It is not fully known how HLA-B27 increases the risk of developing ankylosing spondylitis.

Variations in several additional genes, including ERAP1 gene, IL1A gene, and IL23R gene, have also been associated with ankylosing spondylitis. Although many of these genes play critical roles in the immune system, it is not fully known how variations in these genes affect a person's risk of developing ankylosing spondylitis. Changes in genes that have not yet been identified also likely affect the chances of developing ankylosing spondylitis and influence the progression of the disorder. Researchers are working to identify these genes and clarify their role in ankylosing spondylitis.

Genes Associated with Ankylosing Spondylitis

  • CARD9
  • ERAP1
  • HLA-B
  • IL1A
  • IL23R
  • STAT3

Additional Information from NCBI Gene:

  • ERAP2
  • IL12B
  • IL17A
  • IL1R1
  • IL1R2
  • IL27
  • IL6R
  • PTGER4
  • TYK2

Inheritance

Although ankylosing spondylitis can occur in more than one person in a family, it is not a purely genetic disease. Multiple genetic and environmental factors likely play a part in determining the risk of developing this disorder. As a result, inheriting a genetic variation linked with ankylosing spondylitis does not mean that a person will develop the condition, even in families in which more than one family member has the disorder. For example, studies show that about 75 percent of children who inherit HLA-B27 from a parent with ankylosing spondylitis do not develop the disorder.

Other Names

  • axial spondylarthritis
  • Bechterew disease
  • Marie-Struempell disease
  • SpA
  • Spondylarthritis ankylopoietica
  • Spondylitis ankylopoietica
  • spondyloarthritis
  • Spondyloarthritis ankylopoietica

Frequently Asked Questions

Unlike typical mechanical back pain, which often improves with rest and worsens with activity, ankylosing spondylitis (AS) pain characteristically worsens with rest or inactivity, especially in the morning or after prolonged sitting. It tends to improve with physical activity and exercise. AS pain is also often accompanied by stiffness that lasts for more than 30 minutes in the morning and can involve the buttocks or hips, not just the lower back.
Regular exercise, particularly activities that promote spinal mobility and strength like swimming, yoga, or Pilates, is essential to combat stiffness and maintain flexibility. Avoiding smoking is crucial as it can worsen disease activity and progression. While no specific diet cures AS, some individuals find that an anti-inflammatory diet (rich in fruits, vegetables, lean proteins, and healthy fats, while limiting processed foods and refined sugars) can help manage symptoms. Maintaining a healthy weight also reduces stress on joints.
Diagnosis involves a combination of clinical evaluation, imaging, and blood tests. A doctor will assess symptoms, particularly chronic inflammatory back pain and stiffness. Imaging tests like X-rays of the sacroiliac joints are crucial to look for signs of inflammation or fusion. MRI scans can detect earlier signs of inflammation not visible on X-rays. Blood tests may check for inflammatory markers (like C-reactive protein and ESR) and the presence of the HLA-B27 gene, which is common in people with AS, though not everyone with the gene develops the condition.
Treatment aims to reduce inflammation, relieve pain, prevent spinal damage, and maintain mobility. Beyond over-the-counter pain relievers, nonsteroidal anti-inflammatory drugs (NSAIDs) are often the first-line treatment. For more severe or progressive disease, biologic medications, such as TNF inhibitors or IL-17 inhibitors, are highly effective in slowing disease progression and reducing inflammation. Regular physical therapy and exercise are also critical to maintain spinal flexibility and posture.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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