Ankylosing spondylitis is a type of arthritis. It often begins in the area where the spine meets the pelvis and particularly in the sacroiliac joints. It causes pain and stiffness and may affect the shape of the spine and mobility.

Symptoms and physical findings of ankylosing spondylitis (AS) can be present in other parts of the body, as well as structures in close proximity to the spine. For instance, in time, the bones in the spine and the chest can fuse together, leading to difficulties moving and breathing.

Early diagnosis and treatment can help manage the symptoms and reduce the risk of spinal deformity and other complications.

MRI of suspected ankylosing spondylitisShare on Pinterest
Design by MNT; Photography by Weber et al., CC BY 2.0, via Wikimedia Commons

AS mainly causes pain and swelling in the joints of the lower back, where the spine meets the pelvis, but it can also affect other joints.

The main symptoms are:

  • pain in the lower back, hips, and buttocks that can take several weeks or months to develop
  • pain, swelling, redness, and warmth in the toes, heels, ankles, knees, ribs, upper spine, shoulders, and neck
  • stiffness on waking or after resting for some time
  • back pain during the night
  • back pain that lasts longer than 30 minutes after waking up
  • fatigue
  • a loss of appetite

Back pain may improve after activity.

According to the Spondylitis Association of America, symptoms usually start between the ages of 17 and 45 years, but they can appear in children and older adults as well.

Symptoms can vary widely between individuals. In females, for example, symptoms may appear in areas other than the lower back, such as the knees and ankles.

Around 1 in 10 people with the condition experience symptoms so severe that they are at risk of long-term disability.

Some common early signs and symptoms include:

  • pain in the lower back, hips, and buttocks
  • stiffness in the lower back, hips, and buttocks
  • neck pain
  • ligament and tendon pain where these structures attach to the bones
  • tiredness
  • night sweats
  • mild fever
  • appetite loss
  • general discomfort

These symptoms may:

  • develop gradually over several weeks or months
  • be more prominent in the morning or during the night
  • be worse after periods of inactivity
  • improve after light exercise or a warm shower
  • appear or intensify at irregular intervals
  • affect one or both sides of the body

AS is a chronic condition, which means that it is present all the time or constantly recurs. However, symptoms may improve at times and then worsen again during a flare.

When AS flares up, a person may notice the following:

  • fatigue
  • a fever
  • worsening joint pain
  • back pain and stiffness
  • enthesitis, a type of inflammation of the connective tissue where tendons and ligaments meet the bone
  • emotional symptoms, such as anger and depression

Flares can be localized, where pain mostly affects a specific area of the body, but they can also be general, causing flu-like symptoms and discomfort throughout the body, as well as hot, burning joints, muscle spasms, and increased sensitivity.

Flares are common. According to a 2010 study, around 70% of people with AS reported a flare in any given week. In another study, people with AS said that they had around one flare a month and that each flare lasted around 2 weeks.

While it is unclear what causes a flare, physical or emotional stress may play a role.

There are links between AS and inflammatory bowel disease (IBD), which includes Crohn’s disease and ulcerative colitis. According to one source, 7% of people with AS will develop IBD.

Symptoms of IBD include:

Anterior uveitis, or iritis, is an eye condition that may affect up to 33% of people with AS at some time in their life. Uveitis involves inflammation between the cornea, at the front of the eye, and the lens.

Symptoms usually start suddenly and include:

  • eye pain
  • sensitivity to light
  • red and sore eyes
  • blurred vision

Uveitis can last several weeks, but it should not last longer than 3 months. This symptom can recur following resolution.

Anyone who may have symptoms of uveitis should seek medical attention within 24 hours to get treatment as soon as possible and reduce the risk of complications.

Complications and less common symptoms include:

Fusing of joints

Inflammation in the bone and joints can eventually cause new bone tissue to form and bones to fuse together, especially at the base of the spine. This can lead to stiffness and difficulty moving.

Chest and lung problems

Inflammation in the joints of the rib cage can lead to pain and stiffness in the chest, which may feel like angina or a lung problem. Over time, it can become harder for the rib cage to expand, and this can affect breathing.

Less commonly, scarring can occur at the top of the lungs. This can affect the way the lungs work, and make it harder to recover from colds and other respiratory diseases.


Enthesitis is inflammation that occurs where the ligaments attach to the bone, leading to swelling and tenderness. It often affects the heel, but it can also occur throughout the body.


People with AS and other types of chronic inflammation have a higher risk of anemia. Symptoms include fatigue. Anemia can have a significant impact on a person’s quality of life.

Heart inflammation

Inflammation of the aorta, the body’s largest artery, can occur in those with AS. The aorta carries blood from the heart to the other areas of the body. When the aorta becomes inflamed, this can affect its functioning.

Osteoporosis and spinal problems

Chronic inflammation can lead to a weakening of the bones and osteoporosis. The risk of low bone mineral density and spinal fracture may be seven times higher in people with AS than in those without it.

This increases the risk of spinal compression fracture. It can also affect posture and increase the risk of injury to the spinal cord and nerves.

Neurological complications

In rare cases, AS may cause scarring on the nerves at the base of the spine, resulting in cauda equina syndrome. It can affect bowel and bladder control and sexual function, and there may be weakness in the legs.

AS is a type of arthritis that often starts in the area where the spine meets the pelvis. However, it can also affect joints throughout the body. It also increases the risk of other conditions, such as IBD and uveitis.