Enthesitisassociated Arthritis

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The term spondyloarthropathy does not refer to a specific disease. Meaning "arthritis involving the back," it describes a pattern of inflammation that may occur in children with a variety of underlying conditions. For many years, children with spondyloarthropathies were considered to have JA, but now these children are described as having enthesitis-associated arthritis. Although enthes-itis-associated arthritis is considered a subtype of juvenile arthritis, it is important to recognize that this is a very different disease from, for example, pauciarticular-onset arthritis. Remember, juvenile arthritis is being used as an umbrella term encompassing a large number of different conditions. In contrast to other types of arthritis, the spondyloarthropathies have a different pattern of joint involvement, a different prognosis, a different best medication, and a different cause.

The first widely recognized group of children with spondyloarthropathies were teenage boys with swollen knees and low back pain. They stood out because under the old nomenclature they were classified as pauciarticular-onset arthritis, even though typical pauciarticular-onset arthritis occurs in young girls. We now know that teenage boys with swollen knees have spondyloarthropathies. (The condition does occur in girls, but rarely in severe form.) Unlike young girls with pauciarticular-onset arthritis, who usually get better, the boys often have persistent chronic arthritis. The boys rarely are ANA-positive, and if they get eye disease, it is acute and painful, not the silent eye disease seen in younger children. In addition, their disease may start in the hip and is often associated with back pain.

When rheumatologists began to look more carefully at this group of teenage boys, they discovered that they often had inflammation in the tendons around the joint (enthesitis) as well as in the joint. Recognition that these boys were different was hastened by the discovery of HLA B27, a genetic marker that is found in about half of this group but only infrequently in young girls with arthritis. Once this group was recognized, pediatric rheumatologists realized that spondyloarthropathies with pain due to inflammation of the tendon insertions (often without obvious arthritis) are common in childhood.

Spondyloarthropathies typically begin in the early teenage years and are often mistaken for recurrent athletic injuries. Unlike typical pauciarticular-onset arthritis, in which it is uncommon for there to be another affected family member, other family members of children with spondyloarthropathies are frequently found to be symptomatic. The affected relatives have had chronic back or knee problems since they were teenagers that they attribute to injuries or other vague causes; they often are unaware that these are signs of a specific medical condition.

The significant findings in children with spondyloarthropathies often relate to tendon inflammation rather than arthritis. Enthesitis causes pain around the wrists, knees, ankles, or heels. Frequently, physicians are confused because the child is complaining of a lot of pain, but nothing is broken and the joint is not swollen. Careful palpation around the joint will often reveal the painful tendo-nitis. Sometimes the tendons are very swollen and easily noticed on examination. In other cases the tendonitis is obvious only when the tendons are compressed and the child says it hurts.

Pain around the joint (periarticular pain) is the hallmark of spondyloarthropathies. The key to recognizing that the child is not suffering from recurrent athletic injuries is that multiple tender joints are present (for example, it's not just the left ankle that hurts; the right ankle, heel, low back, and wrist may also be tender when examined). Another common finding is pain at the Achilles tendon insertion on the back of the heel or at the insertion of the plantar fascia on the bottom of the foot (see Fig. 7-1). This can be detected by percussion or deep palpation at either point. Discovering that there are similarly affected family members when taking the family history also may speed recognition of a spondyloarthropathy.

Dactylitis (sausage digit) may be the first manifestation of a spondyloarthropathy in both young children and teenagers. Instead of the joints, the entire finger or toe appears swollen, like a sausage. This is because of swelling around the inflamed tendons as well as the joint. At first, the child is complaining of only a single finger or toe and is initially thought to have injured it. However, on careful examination, periarticular involvement is often evident in multiple joints.

Heel Insertion
FIG 7-1 Pain in enthesitis-associatedarthritis commonly occurs at the back of the heel (Achilles tendon insertion) or bottom of the heel (plantar fascia insertion).

Often there is unrecognized inflammation in toes on the same side as the finger that can be found by careful examination. It is also common to find unsuspected wrist involvement on the affected side. These children may be ANA-positive and may have unsuspected eye inflammation. It is important that they be properly screened for eye disease (see Chapter 6).

In teenagers, difficulty bending forward to touch the toes is an additional finding that assists in making this diagnosis. Frequently, physical education instructors have noted that they are not flexible. Sacroiliac joint tenderness is another common finding.

Laboratory findings may not be helpful. Although severe cases may have an elevated sedimentation rate, all tests are often normal in children with mild spondyloarthropathies. HLA B27 is present in about one-half. Rheumatoid factor should never be present. ANA is present in some (see Chapter 22).

Once a child is diagnosed with a spondyloarthropathy, it is important to recognize that this pattern of joint involvement may be associated with a variety of other diseases (discussed later). Many children have a nonspecific spondyloarthropathy, meaning there is no associated condition. However, the associated condition may not become evident until years after the arthritis begins. It's important to be aware of these associations so that the child can be evaluated appropriately. This is particularly true of children who develop recurrent abdominal pain that might be inflammatory bowel disease (IBD); while most children with IBD develop arthritis after their bowel disease is recognized, this is not always the case.

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