Juvenile arthritis, or JA, is a chronic inflammatory condition diagnosed in children, ages 16 and under, with an annual incidence of around three to six instances per 100,000 children. Enthesitis-related arthritis is a type of JA accounting for approximately 10 to 15 percent of all cases.  It is typically diagnosed between the ages of 8 to 15 and is more common in boys.

In addition to the joint swelling and inflammation associated with JA, patients with this specific type of JA also experience enthesitis—which is defined as the inflammation of the entheses, or the connective tissue joining tendons and ligaments to bone. Enthesitis-related JA is an autoimmune disease. Although the cause is unknown, genetics, environmental factors, and malfunction of the immune system are all believed to play a part.

How does enthesitis-related JA affect the body?

Enthesitis-related JA commonly causes inflammation and ethesitis, around the hip, knee, and ankle joints, and can occasionally affect the feet and toes as well. Symptoms of pain and swelling can be intermittent. Arthritis may also develop in the back and neck as the disease progresses.

Inflammation also occurs in the iris of the eye, termed acute anterior uveitis, in approximately 30 percent of patients. This type of uveitis causes redness, pain, and sensitivity to light and can result in lasting optical damage if not addressed. Psoriasis, or skin inflammation, and inflammatory bowel disease in the form of Crohn’s disease and ulcerative colitis are also know effects of enthesitis-related JA.

How is enthesitis-related JA diagnosed?

To assess a patient for enthesitis-related JA, a physician will complete a physical examination, specifically looking for joint inflammation and pain in the lower limbs, lower back, or buttocks. X-ray or magnetic resonance imaging (MRI) may be completed to confirm suspected soft tissue damage around affected joints.

The genetic marker HLA-B27 is generally correlated to the development of the disease, so physicians may request a blood test to determine the presence or absence of the marker. HLA-B27 is also associated with ankylosing spondylitis or inflammatory bowel disease, so a family history including either of these diseases can similarly be an indicator. Although HLA-B27 and enthesitis-related JA are linked, some patients who are negative for the genetic marker may have the disease, and, conversely, not all patients with enthesitis-related JA test positive for HLA-B27. A diagnosis should not be made based on the results of this test alone.

How is enthesitis-related JA treated?

Physicians will typically first try to treat the disease with nonsteroidal anti-inflammatory drugs (NSAIDs). Many rheumatologists prescribe Indocin-based NSAID therapies for enthesitis, however, not all of these medications are approved for children. If this appears to be ineffective, physicians may prescribe therapies including disease-modifying anti-rheumatic drugs (DMARDs) or biologics.