Ankylosing spondylitis causes chronic pain in the joints, usually starting in the back and buttocks.

No single test can diagnose ankylosing spondylitis (AS), but a range of questions and techniques can help confirm or rule out a diagnosis.

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The doctor will start by asking the person about their symptoms and health history. A few specific signs and symptoms may point to the early signs of AS.

Is there a family history of AS?

If there is a history of AS in a person’s family, they are more likely to have it, although this is not always true.

The doctor will still need to carry out thorough exams before making a diagnosis.

Is there unexplained pain that appears gradually?

AS often appears before the age of 45 years. Unexplained pain and stiffness is less common in younger people.

A doctor may consider AS if a young person has pain, especially back pain and pain in the buttocks that have no known cause.

For example, if the person has not had an injury or put undue strain on their back, they may have AS.

The pain often develops over several weeks or months. It may start as a slight stiffness and gradually grow into aching, stiff joints and reduced mobility in the spine.

A history of back pain lasting for 3 months or more may be a key factor in diagnosis.

Is pain worse when sleeping or prone?

With many conditions, chronic back pain improves when resting. The opposite is true with AS.

People with AS will experience more pain when resting. It can worsen during the night, and be the most pronounced upon awakening. It may ease as the person moves around throughout the day.

Some people with AS have pain that comes and goes, but others have severe and persistent pain.

Does pain improve with physical motion?

The pain caused by AS is also different from other types of back pain because exercise makes it better, not worse.

Exercise and stretching can irritate other people with back pain, but someone with back pain caused by AS will feel relief after stretching or doing other forms of exercise.

Do NSAIDs treat the pain?

In the early stages of AS, over-the-counter drugs such as ibuprofen or prescription non-steroidal anti-inflammatory drugs (NSAIDs) will ease the pain. They are usually not enough to deal with the disorder over time.

However, if a person’s symptoms initially get better with NSAIDs, they may have AS.

Is chest expansion reduced?

Some individuals with AS will also experience chest pain and stiffness. The ribcage may feel tight and not expand as much as the doctor would expect. This can make it hard to breathe and can lead to an increase in lung infections.

Are there signs of inflammation?

Others may have stiff joints, pain in their ankles or heels, or inflammation in their wrists. Inflammation of the sacroiliac joints, which connect the base of the spine to the pelvis, is a sign of AS.

Some people may experience these symptoms, which can also be signs of inflammation:

  • a fever (not common)
  • tiredness
  • hot, red joints

Are there other symptoms?

Other symptoms associated with AS include:

  • inflammation of the eye and vision changes
  • abdominal pain and bowel changes
  • general tiredness
  • skin rashes, particularly on the soles of the feet
  • psoriasis, if a person has the psoriatic arthritis form of spondyloarthritis
  • low appetite and weight loss

Knowing if a person has any of these symptoms helps a doctor decide whether they have AS.

Doctors will often ask these questions to find out if they should continue to the next step of diagnosing AS, which is usually a physical exam.

No single test can show that a person has AS. Doctors use a range of methods to help make the diagnosis.

Genetic tests

One test is specific to AS. It is the HLA-B27 test, which can detects the HLA-B27 gene. A doctor will take a blood sample to carry out this test.

This genetic factor is present in many people who have AS, and those who have the gene may be more likely to develop the condition.

However, this is not always the case. Around 80% of people who inherit the genetic feature from a parent will not develop AS, and the risk also varies with ethnic background.

Blood tests for inflammation

A blood test can also detect signs of inflammation in the body. Those tests include an erythrocyte sedimentation rate (ESR) test or the C-reactive protein (CRP) test.

While these tests can spot common signs of inflammation in the body, they will not specify that the inflammation is due to AS.

Physical exam

During the physical exam, the doctor will usually check for signs of inflammation in the person’s body.

Typically, a doctor will look at the back, chest, pelvic bones, sacroiliac joints near the bottom of the spine, and the heels. They may press gently into these areas and ask about any pain and tenderness.

The doctor will also check the range of motion of the spine. They may ask the person to do some mobility tests to see if there is any restriction of movement.

They may also assess how far the chest expands and how easy it is to breathe, and the range of motion of the cervical spine (neck).

Imaging and scans

After looking for signs in the blood, doctors will often use X-rays or MRIs.

X-rays may show if joints are damaged or fused. The X-ray may focus on the sacroiliac joints, where AS often appears.

An MRI scan or ultrasound can reveal changes that do not show up on an X-ray, such as inflammation without joint damage. Signs of inflammation include a widening or thinning space between bones, or increased blood flow, which equates to inflammation.

Imaging can help confirm the presence of AS and help people make treatment decisions. It can also help track changes over time.

No single test can diagnose AS, but a doctor will use findings from tests and the information a person gives about key symptoms to decide whether AS is likely to be present. They will consider factors such as:

  • swollen and painful joints, especially around the spine
  • fatigue
  • whether pain occurs on awakening, and how long it lasts

They may use a scoring system to assess levels of pain and disease activity.

A doctor may confirm that a person has the condition if they have inflammation of the sacroiliac joint and one or more of the following:

  • have had back pain for 3 months or longer that improves with exercise but not with rest
  • have limited movement in the lower back
  • have limited chest expansion for their age and sex

If a person has all three features but not inflammation of the sacroiliac joint, or if they only have inflammation of the sacroiliac joint, a doctor may diagnose probable AS.

Treatment aims to reduce the symptoms, slow the progression of AS and improve a person’s functionality.

Treatment plans will typically include:

  • NSAIDs to manage pain and inflammation
  • TNF-a inhibitors and other biologic drugs that can slow the progression of AS
  • physical therapy, exercise, and techniques to manage posture and improve the flexibility of the spine and other affected joints
  • breathing exercises to help expand the chest

A doctor may recommend low-impact activities that provide a full-body workout, such as swimming and cycling.

People should see a doctor if they have pain in the lower back, hips, or buttocks, especially if the pain is severe, persists or worsens over time, or primarily occurs upon awakening.

They should also seek medical advice if they experience any other symptoms or complications of AS, or if those symptoms worsen.

Slowing the progression of AS and managing symptoms is often possible with medical treatment.

No single test can diagnose AS, but doctors will look at a range of factors.

These include symptoms, personal and family medical history, and the results of imaging tests, blood tests, and possibly genetic tests.

Getting an early diagnosis can help a person access suitable treatment. This will increase their chances of managing the condition, maintaining a good quality of life, and preventing disease progression.