Ankylosing spondylitis (AS) is a form of arthritis that mainly affects the spine, lower back, and sacroiliac joints. Early signs include pain and stiffness in the lower back, the hip area, or both. The pain may last for several weeks or months.

AS is an inflammatory condition. Characteristic symptoms include joint pain, stiffness, and a loss of mobility in the spine and pelvis.

The condition involves inflammation where the ligament and tendons attach to the bones of the spine and the bones of the peripheral joints, known as the entheses.

This inflammation increases bone formation in the spine, leading to bone fusion. In advanced cases, this can also lead to spinal deformity.

This article explains AS, including its symptoms, treatments, causes, complications, and associated exercises.

A diagram showing the differences between a regular spine and the spine of a person with ankylosing spondylitis (AS). In AS, the vertebrae are inflamed and fused together. The natural curvature of the spine is also affected. Share on Pinterest
A diagram showing the differences between a regular spine and the spine of a person with ankylosing spondylitis (AS). In AS, the vertebrae are inflamed and fused. The natural curvature of the spine is also affected. Infographic by Jason Hoffman.

AS is a type of arthritis. It mainly affects the lower part of the spine and where the spine joins to the hips, known as the sacroiliac joints.

AS can be challenging to diagnose, but it has a particular pattern of pain symptoms, and the changes are often visible in X-ray and MRI scans.

Males may be more likely to have severe inflammatory disease, though females with AS may be underdiagnosed. According to the Spondylitis Association of America (SAA), symptoms usually begin between ages 17 and 45.

However, symptoms can also develop in children and people who are much older.

There is no cure for AS, but certain drugs can help manage pain and inflammation. Physical therapy can relieve pain and prevent or delay limitations and decreased mobility.

The most common early symptoms of AS are frequent pain and stiffness in the lower back, the hip area, or both. These symptoms may occur over several weeks or months.

Over time, these symptoms may spread to other areas of the spine and can affect the neck’s spinal joints.

AS can cause symptoms that include:

  • spine and midback pain
  • spine and midback stiffness
  • a loss of mobility
  • pain that worsens with rest and during the night
  • pain that improves with movement
  • pain that affects other joints
  • fatigue, which refers to a feeling of being tired and lacking energy
  • appetite loss
  • vision changes
  • abdominal pain and diarrhea
  • trouble taking deep breaths

Some people have mild pain that comes and goes, while others have severe, prolonged pain. Everyone with AS is likely to experience flares — when the symptoms worsen — and periods of remission where symptoms improve.

Learn more about the early signs of AS.

AS can also affect other parts of the body. These include the areas around other joints, such as the:

  • ribs
  • shoulders
  • knees
  • ankles, feet, and tendon insertions at the heel
  • top of the shin bone in the lower leg
  • Achilles tendon
  • sternum

Learn more about how to recognize symptoms of AS.

The exact cause of AS remains unclear, but the early symptoms result from inflammation in parts of the pelvis.

AS may have genetic and environmental components. Researchers believe that people with specific genes may develop AS after exposure to a trigger, such as a virus or bacteria.

About 90% of people with AS have the HLA-B27 gene. AS often runs in families.

Risk factors can include:

  • being age 45 or under
  • having a family history of AS
  • having health conditions that include Crohn’s disease, ulcerative colitis, or psoriasis

To diagnose AS, a doctor typically asks about the person’s symptoms, performs a physical examination, and arranges for tests when necessary.

If inflammatory back pain has certain features, it may indicate AS.

These features include:

  • pain that does not improve with rest
  • pain that causes sleep disturbance
  • back pain that starts gradually, between the ages of 17 and 45 years, and is not due to injury
  • symptoms that persist for several months
  • spinal stiffness in the mornings, which seems to improve with exercise and motion
  • pain that improves with a warm shower

Imaging tests for AS may confirm the diagnosis, but changes may not be immediately visible on such tests. This can delay diagnosis.

The section below examines blood and imaging tests in more detail.

Learn more about the diagnostic criteria for AS.

Blood tests

No blood test can confirm AS, but some tests can rule out other causes of the person’s symptoms.

A reported 90% of people with AS have a genetic marker called HLA-B27. Doctors may order a blood test for this as a part of the initial workup.

The tests for inflammation may include:

Imaging tests

These may include:

  • X-rays, which can reveal both early and more advanced changes to the spine and pelvis
  • MRI scans of the sacroiliac joints, which can reveal early signs of AS
  • ultrasound, which can show peripheral joint and tendon inflammation

There is currently no cure for AS. However, treatment can help relieve symptoms and manage the condition’s progression.

Treatment options include:

  • physical therapy, occupational therapy, and exercises
  • certain drugs
  • surgery, in rare cases, as surgery can increase bone formation

People with a diagnosis of AS typically need to consult a doctor known as a rheumatologist. They may require several visits as the condition progresses slowly, and consistent medical care allows better monitoring and treatment.

Doctors only recommend surgery to correct severe deformities, such as excessive posture changes due to inflammation and ankylosing of the spine, or replace a hip or other joint. This typically requires collaboration between a rheumatologist and an orthopedic surgeon.

Drug treatment

The main medications that people use to ease the pain and inflammation of AS are nonsteroidal anti-inflammatory drugs (NSAIDs). Some examples include:

Some NSAIDs compromise bone health by reducing the creation of new bone, so doctors do not usually recommend NSAIDs after surgery for people with bone fusion problems. However, they may benefit people with AS who have hypertrophic bone formation.

Some other drug options include:

AS can affect the whole body, and a person may need coordination of care by several specialists, including:

Learn more about the drug treatments for AS.

A common complication of AS is inflammation of the eyes, causing pain and redness. This inflammation, known as iritis or uveitis, can impair vision without treatment.

In severe cases, AS can cause the vertebrate of the spine to fuse, or “ankylose.” This can make performing everyday tasks challenging. Fusion of the bones can also lead to curvature of the spine, although this is far less common now due to advances in treatment.

Sometimes, AS can also restrict chest movement and make breathing difficult.

AS can increase a person’s risk of osteoporosis and fractures. If a person has had AS for a long time or the bones have fused, they may also be at risk of fracturing bones in their back.

About 15% of people with AS experience jaw inflammation, making it difficult to open their mouths to eat. At the same time, around 6–14% of people experience inflammatory bowel disease (IBD).

Learn more about the effects of AS on the body.

Other rarer complications of the condition may include:

  • aortic regurgitation,where the heart’s aortic valve does not close tightly
  • pulmonary fibrosis, a type of lung disease where the tissue is damaged or scared
  • cauda equina syndrome, where the nerves in the back become severely compressed

Chronic pain and AS symptoms can cause people to experience depression and other mood disorders.

Learn more about the possible complications of AS.

Although living with AS can present challenges, people can adapt to living with the condition.

Lifestyle

According to the National Institute of Arthritis and Musculoskeletal Diseases (NIAMS), research shows that people involved in their care report less pain and enjoy a better quality of life.

People can practice self-care by:

  • learning about the disease and its treatments
  • seeking support for the physical and mental effects of AS
  • communicating with health teams to enable the best care for their condition

People can also try numerous lifestyle changes and activities to improve function and increase their understanding of and autonomy over their condition. These include:

The SSA offers further resources and support for people living with AS, including support groups, educational resources, and community forums.

Exercises

Physical therapy and exercises can help treat the symptoms and prevent or delay mobility limitations.

A physical therapist can design a program to help a person maintain good posture and joint motion.

This might consist of:

  • daily exercises
  • special training to address areas of involvement
  • therapeutic exercises

Physical therapy exercises are known as strengthening exercises and range-of-motion exercises.

The SSA notes that an ideal exercise program includes the following four elements:

  • Stretching: Stretching can improve flexibility and reduce muscle stiffness, swelling, and pain. It can also minimize the risk of joint fusion.
  • Cardiovascular exercises: These exercises include swimming and walking. They can improve lung and heart function and reduce pain and fatigue.
  • Muscle exercises: These help strengthen the core and back muscles, which help support the spine. Having strong muscles can improve posture and movement, as well as reduce pain.
  • Balance training: This can help improve stability and reduce the risk of falls.

Some doctors may also recommend swimming or water exercises if a person has access to a pool. They can help individuals maintain flexibility while minimizing the injury risk during exercise.

Learn more about specific exercises for AS.

Diet

Doctors might also recommend specific diets, foods, or nutrients to help a person manage the symptoms of AS.

This may include:

  • an anti-inflammatory diet based on whole foods, such as the Mediterranean diet
  • weight loss, if needed, to reduce stress on the bones and joints
  • avoiding foods that promote inflammation, such as ultra-processed foods

More research is needed on the benefits of following a specific eating plan for AS.

Learn more about diet and AS.

The outlook for AS is difficult to predict because it varies widely from person to person, and the progression is often not constant. Important factors for measuring outlook include levels of functional ability, spinal mobility, and joint damage.

Some people experience severe functional loss, while others hardly notice their symptoms. In contrast, some people may have life threatening complications that affect the heart, lungs, or nervous system.

Smoking can lead to poorer outcomes.

AS is a type of arthritis that affects the spine and lower back. It tends to appear in late adolescence or early adulthood.

Although there is no cure for AS, many treatments can help slow or stop the progression. Daily management, such as an exercise program, can help people control their symptoms.