Ankylosing spondylitis: X-ray and imaging techniques
Imaging helps doctors recognize signs of ankylosing spondylitis and to recommend treatment.
There are a few different methods that are used in the process. There may also be some risks for people to consider.
Ankylosing spondylitis (AS) is a chronic inflammatory disorder that most commonly affects the back and sacroiliac joints. These joints are made up of the bones near the hips and lower back called the sacrum and ilium.
AS causes stiffness and pain that can get progressively worse. As the condition progresses, ankylosis can occur.
Ankylosis is the process of a joint becoming stiff or fixed, or of bones fusing together.
In cases of progressing AS, it is normal for one or more bones in the spine to fuse together. The sacroiliac joints may fuse together completely.
There are other occurrences of ankylosis in AS. However, these types of fusing are just two of the signs doctors look out for when using X-rays or other imaging techniques to check for AS.
Use of radiography in diagnosing AS
X-rays produce high-energy light that can penetrate through objects that normal light cannot. The waves of light given off by X-rays can pass through hair and skin, but are blocked by bones.
When a part of the body is scanned with an X-ray, an image of the inside of the body is produced. X-rays are commonly used in medical fields to monitor teeth and bones. The process of taking these images is called radiography.
X-rays and radiography are very important in diagnosing and monitoring AS.
When a doctor or rheumatologist suspects a person has AS, they will usually take some blood tests and order X-rays of the spine and sacroiliac joints.
Problems in the sacroiliac joints are hallmarks of AS, meaning that any symptoms appearing in the sacroiliac joints are strong indicators that someone has AS.
Typical signs include a widening or thinning of the sacroiliac joint. In a person who has AS that has progressed, the joint may appear very thin or not visible at all.
Doctors also take images of the spine to help them with a diagnosis. The hallmarks of spinal problems in AS are small bony spurs called syndesmophytes, which are thin projections of bone that stick out from the corners of the vertebrae.
Inflammation caused by AS can continue moving up the spine as the condition progresses. Doctors will use X-rays to look out for these signs. The joints on each bone in the spine can become inflamed, eventually leading to two or more bones fusing together.
In those who have difficulty breathing, doctors will take an image of the joints where the ribs connect to the spine. The joints here can become fused and severely limit the breathing and lung capacity of the patient. This will often affect posture as well.
Doctors use these X-rays to help them diagnose AS, but they are also helpful if a person already knows they have AS. The images allow doctors to see how far the disorder has progressed. This can help with creating a treatment plan, especially in cases where drug options are being considered.
Other imaging techniques
X-rays are the most common way for doctors to get a look at the bones, but they are not the only imaging techniques used for diagnosing AS. A few other techniques that may be valuable for rheumatologists and people with AS alike include CT scans, MRIs, and ultrasonography.
In some cases, doctors may request a computed tomography scan, or CT scan. A CT scan takes a series of X-rays and puts them together to get a better look at the bones and tissues inside the body. CT scans are more reliable, and they create more high-resolution images than X-rays do.
CT scans can provide a more complete picture in cases where X-rays images are inconclusive or appear normal. Certain signs of AS may be more apparent on a CT scan as well, such as eroding joints or areas where ankylosis is occurring.
The primary use for CT scans in AS is to see and define where bones and joints have worn away and to look for any fractures.
The use of CT scans is still somewhat limited for cases of AS, however. This is because CT scans require a heavier dose of radiation than X-rays and MRIs, and they can give an incomplete picture.
Furthermore, CT scans are not as good at detecting soft tissues, so any damage being done to soft tissue may go unnoticed until it causes structural damage in the body.
MRI stands for magnetic resonance imaging. MRI uses a magnetic field and radio waves to take pictures of the inside of the body.
MRI machines are very sensitive and can provide better soft-tissue contrast in images than other options. This makes them ideal for taking images of organs or other soft tissues.
MRI is the most sensitive form of imaging available for cases of AS. The sensitivity of MRI allows doctors to detect or track inflammation in the bones or other soft tissues.
It is the easiest imaging technique for spotting early symptoms in the spine and sacroiliac joints, including those that are missed by X-ray and CT scans.
Ultrasonography (US) has limited use in diagnosing ankylosing spondylitis. US may be used by a rheumatologist to find other complications associated with the disorder, but the other imaging techniques described here will be used for the symptoms of AS itself.
Some people may be concerned about using X-rays and CT scans because of the radiation they emit.
People experience radiation every day from X-rays in our environment. But X-rays and CT scans can expose the body to a higher level of radiation than normal. This radiation can cause mutations in human DNA that may lead to cancer later in life.
Consequently, X-rays and CT scans are deemed to have the potential to cause cancer. However, the actual increased health risk associated with radiation exposure from normal X-ray or CT scans appears to be low, according to the United States Food and Drug Administration.
With normal exposure to X-ray and CT scan radiation, there seems to be very little increased risk for developing cancer at a later stage.