There are conditions that fall under the SpA grouping. These include:
- Enthesitis-related arthritis
- Juvenile ankylosing spondylitis (JAS)
- Reactive arthritis
- Arthritis associated with inflammatory bowel disease (IBD) and psoriasis (see table 1 below)
Each will be looked at on its own, as they differ in crucial ways.
Enthesitis-Related Arthritis (ERA)
In many children and adolescents, ERA starts as arthritis in the large joints of the lower extremities, mainly the hips and knees. It is also common to have pain and feel tender due to inflammation where tendons or ligaments attach to bones. This is called “enthesitis.” Common sites for this inflammation are at the heel, the top and bottom of the kneecap (patella), the ball of the foot and bottom of the foot at the heel (plantar fascia). Also, in some patients with ERA, inflammation in the joints of the foot, mainly in the mid-foot zone (tarsitis), is seen. It is not common for arthritis to occur in the elbows and wrists, but it does occur in the shoulders. Sometimes patients with ERA will have inflammation in other parts of their body. Eye inflammation (anterior uveitis) occurs in approximately half of patients. Unlike the inflammation in the eyes seen in other types of arthritis, the uveitis seen in ERA almost always causes pain and redness.
Juvenile Ankylosing Spondylitis (JAS)
JAS is a more fully developed form of SpA in children where the child needs to have developed arthritis in the lower back in either the spinal joints or the sacroiliac joints (sacroiliitis).
Diagnosing JAS can be hard if the spine and/or lower back are not involved when other symptoms start. Since the back concerns may not occur for many years after other symptoms have begun, in this case the child is said to have ERA. In studies looking at children who developed JAS at some point but at first had arthritis that looked just like ERA, it was found that they were more likely to have had lower extremity arthritis and pain and tender feeling where tendons or ligaments attach to bones during the first year of their illness, and often including of the foot (tarsitis).
Thus when many of the symptoms are present but the child has yet to have back pain (sacroiliitis), we most often call it ERA. Some studies suggest that as many as 50 percent of these children will have complete JAS with time either in the late teen years or as an adult. This depends on genetic factors though, and we are not yet able to predict with certainty who with ERA will or will not get JAS.
Reactive Arthritis (ReA)
Reactive arthritis (ReA) most often occurs two to four weeks after an infection in some other part of the body like the GI tract, urinary tract or the genitals. GI infections most often involve diarrhea, belly pain and cramping, and are caused by bacteria like salmonella. Infection in the urinary track or genitals may not be associated with specific symptoms (chiefly in females). The inflamed joints do not have these bacteria, but are still the site where many inflammatory cells collect and cause symptoms for reasons that are unknown. Like other forms of SpA, getting ReA is much more common in people with the genetic marker HLA-B27. This is a gene that is there in about 70 percent to 90 percent of patients with arthritis that affects the spine. ReA in children can be short-lived with full resolution of symptoms, or may continue with a more chronic course. Some patients may go on to develop complete JAS over several years, but again this is hard to predict.
Arthritis Associated with Inflammatory Bowel Disease (IBD) or Psoriasis
Arthritis can happen with either type of IBD − Crohn's disease or ulcerative colitis. The arthritis can involve joints in the arms or legs and/or spinal joints and the sacroiliac (SI). When the spine or SI joints are involved it is most often linked to the HLA-B27 gene. Arthritis is also seen in some but not all people who have the skin disease psoriasis.