Imaging techniques, such as X-rays and MRI scans, can play key roles in monitoring ankylosing spondylitis (AS).

Imaging helps doctors recognize signs of ankylosing spondylitis (AS) and recommend treatment. It also helps them monitor changes over time and adjust the treatment plan.

AS is a chronic inflammatory disorder. It can affect many parts of the body and most commonly affects the back and sacroiliac joints. These are the sacrum and the ilium, and they form the back of the pelvis.

It is important for doctors to monitor AS as it changes over time. To do so, they use imaging technology, specifically X-rays and MRI scans.

Here, learn more about how doctors diagnose AS.

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Treatments can help manage the stiffness, pain, and other symptoms of AS, and these tend to worsen over time. A doctor needs to keep track of any changes that occur and adjust the treatment accordingly.

Anyone with AS needs to attend regular appointments so that a doctor can check for:

  • alterations in disease activity, including inflammation and bone changes
  • the impact of AS on breathing and other functions
  • mobility, especially of the spine
  • any adverse effects of medications
  • complications, such as bowel, eye, cardiac, or skin problems
  • the effect of current treatment

A doctor will advise each person about how often they should attend these checkups.

Contact the doctor about any new or worsening symptoms or if any treatment is ineffective.

X-rays are important for doctors who are diagnosing or monitoring AS.

The technology produces high-energy light that can penetrate objects. The waves of light can pass through hair and skin, but bones block them. This is how X-rays show bones.

A doctor uses these images to check for AS-related changes to the bones. They can reveal the following types of damage:

  • erosion and joint damage indicating inflammation
  • osteoporosis
  • hardening or thickening of the bone
  • new bone formation
  • ankylosis, or the fusing of bones

A doctor may recommend an X-ray of:

  • the spine
  • the sacroiliac joints, which connect the spine and the pelvis
  • the rib cage
  • other areas with pain or stiffness

AS can cause the sacroiliac joints to narrow or widen. Bones and joints may change shape, thicken, fuse, or wear away. As the condition progresses, an X-ray can reveal these types of changes.

The spine may also develop small bony spurs called syndesmophytes. These are thin projections of bone that stick out from the corners of the vertebrae.

Pros and cons of X-rays for AS

X-rays have been the gold standard for diagnosing and monitoring AS for many years. They are also less expensive than MRI or CT scans.

One disadvantage is that an X-ray does not show damage to tissues. Inflammation is a common feature of AS, and it can damage joints and connective tissues. X-rays cannot show whether inflammation is present, while MRI scans can.

In addition, it may take 7–10 years for damage to the sacroiliac joints to show up on an X-ray.

Finally, X-rays of the spine and pelvis involve a relatively high dose of radioactivity to produce a clear image. Repeated exposure over many years may increase the risk of cancer, making X-rays less suitable, particularly for younger people, according to experts.

MRI technology uses a magnetic field and radio waves to take pictures of the inside of the body. No radioactivity is involved.

MRI is the most sensitive form of imaging available for AS. It can reveal:

  • the same bone changes that X-rays can show
  • disk herniation, better known as slipped disks
  • inflammation of the bone and soft tissues
  • damage to soft tissues

These scans may be especially useful for a doctor making a diagnosis, as they can detect early AS symptoms and changes — allowing a person to begin treatment in the early stages. MRI scans can also help doctors monitor the progression of the disease.

The disadvantages: MRI scans take longer and cost more than X-rays.

Imaging alone cannot show whether a person has AS or how it is progressing.

Doctors use a range of approaches for diagnosis and monitoring, including:

  • asking detailed questions about symptoms and any limiting of activities
  • testing mobility
  • checking for complications

Experts are currently looking for new ways to measure the progression of AS. By measuring biomarkers, they may be able to detect changes in inflammation and other activity. However, more research is needed before doctors can use these methods.

As part of a wider set of tools, imaging techniques can help doctors detect and monitor AS. X-rays can show changes to bones, and MRI scans can show changes to bones and soft tissues, as well as the presence of inflammation.

An MRI scan is more expensive and time-consuming than an X-ray, but it shows the presence and progression of the disease earlier and in more detail.

Both techniques can provide valuable information, helping the doctor manage the progression of the disease and treat its symptoms.