AS in Kids and Teens

Reviewed by: HU Medical Review Board | Last reviewed: February 2019 | Last updated: October 2022

Ankylosing spondylitis (AS) is a chronic inflammatory arthritis that causes pain and stiffness in the joints. While most cases of AS are diagnosed in adults, approximately 10-20 percent of people begin to have symptoms before the age of 18. When AS occurs in children or adolescents, it is called juvenile-onset ankylosing spondylitis, or juvenile ankylosing spondylitis (JAS).1

What causes juvenile AS?

The exact cause of JAS remains unknown, although researchers have found some genetic clues and believe that environmental factors also play a role. AS tends to run in families and having a family history of the disease increases a person's risk of developing it. One genetic marker that has been identified as playing a role in the cause of AS is called HLA-B27. It is estimated that 90-95% of Caucasians with AS are HLA-B27 positive. However, not everyone with the HLA-B27 mutation develops AS, and some people with AS do not have the HLA-B27 marker. The link between the presence of HLA-B27 and AS varies greatly among different ethnic groups, with the highest rate of HLA-B27 occurring in Caucasians.2,3

Other genetic factors are also likely to play a role, as well as triggers from the environment. Some youth develop JAS after an infection of the intestines or urinary tract, although others do not have a history of infection.4

How is AS different in children or teens than in adults?

In adults, AS most often begins in the sacroiliac (SI) joints, which are located between the pelvis and the lower spine, causing low back pain and stiffness. However, in children and teens, AS more often begins with peripheral joint involvement, those joints in the arms or legs. AS can also cause inflammation at the points where ligaments and tendons attach to bones, called enthesitis.

In JAS, the enthesitis is more often in the peripheral joints, compared to those who develop AS as adults having more enthesitis along the spine. (Although some adults who develop AS also have peripheral joint involvement.) Younger people with AS are also more likely to have higher levels of C-reactive protein, an inflammatory marker in the blood. 5,6 People who develop AS as juveniles are also more likely to need hip replacement surgery than those who develop the disease as adults.7

What are common symptoms of juvenile AS?

While each person with AS can have different areas of the body that are affected, common symptoms of JAS include1:

  • Stiffness in the joints, particularly in the morning, that improves with activity
  • Pain in the back or buttocks that improves with movement
  • Pain in the knees, heels, or bottoms of the feet that gets worse with activity
  • Swelling in the joints, particularly in the large joints of the legs (hips, knees)

In addition to joint symptoms, children and teens with JAS may experience1:

  • Abdominal symptoms, such as diarrhea, pain, or weight loss
  • Eye pain, redness, or sensitivity to light (photophobia)
  • Fatigue

How is juvenile AS diagnosed?

Diagnosis for JAS begins with a thorough evaluation of symptoms through a medical history and physical exam. Imaging technology, such as x-ray, MRI, or ultrasound, may be used to view the joints and any inflammation that is present. Blood tests are commonly done to rule out other possible conditions that can cause similar symptoms.1 AS tends to take a long time to diagnose, as there is no simple blood test and different people with the condition can have different symptoms.

How is juvenile AS treated?

Treatment for JAS aims to reduce symptoms, prevent worsening of symptoms or joint damage, and improve or maintain quality of life as much as possible. Treatment is tailored to the individual and may include non-steroidal anti-inflammatory drugs (NSAIDs), short-term use of corticosteroids, disease-modifying anti-rheumatic drugs (DMARDs), biologic medications, regular exercise, and physical therapy.1

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