Spondyloarthropathies of childhood.

The spondyloarthropathies of childhood present a diagnostic and therapeutic challenge. It is important to differentiate this group of arthritides from JRA because the nature and frequency of extra-articular complications are quite different, as is the prognosis and the therapeutic approach. JAS is the prototype of the spondyloarthropathies and probably accounts for greater than 75 per cent of all children with diseases included in this category. Unlike adult-onset ankylosing spondylitis, axial skeleton disease (sacroiliac, lumbar spine) is infrequent at onset of JAS and may not develop for months or years after the onset of arthritis in peripheral joints (particularly those of the lower extremity). Enthesitis, the inflammation of the insertion of tendon, capsule, ligament, or fascia to bone, is an important clinical diagnostic feature of this group of diseases. Extra-articular disease, such as rash in psoriatic arthritis, erythema nodosum, weight loss of abdominal pain (in the arthropathies of inflammatory bowel disease), urethritis, conjunctivitis, or Reiter's syndrome help to differentiate these spondyloarthropathies from JAS. Laboratory studies are of little assistance in differentiating JRA from the spondyloarthropathies except that in the latter group, RF is absent and HLA-B27 is frequently present. The high frequency of ANA in JRA contrasts with its corresponding low frequency in JAS. The long-term follow-up of chronic arthritis in childhood has demonstrated the variable and evolving nature of these conditions, and stresses the importance of continually questioning the accuracy of the diagnosis.