Juvenile spondyloarthropathies: clinical manifestations and medical imaging.

The spondyloarthropathies comprise four distinct entities--ankylosing spondylitis, psoriatic arthritis, the arthritis associated with inflammatory bowel disease, and Reiter's syndrome and other related forms of reactive arthritis. Although these are distinct diseases, they have a number of clinical, radiologic, and genetic characteristics in common which permit them to be classified under the unifying term "spondyloarthropathy". They are diseases of young adults, and when they present in patients under 16 years of age we refer to them as the "juvenile" spondyloarthropathies. They must be distinguished from juvenile rheumatoid arthritis, which is a totally separate entity; however the distinction may not always be obvious. Involvement of peripheral and sacroiliac joints commonly occurs in the juvenile spondyloarthropathies. The peripheral arthritis may be erosive and associated with bone apposition at the joint margins. Axial involvement is usually a late finding. Dactylitis and tenosynovitis are frequently present early on. Enthesitis, a highly specific feature, occurs much more often in the juvenile spondyloarthropathies than in the adult forms and it may be the only presenting feature. The plain radiograph is the primary and most important imaging modality for the assessment of these diseases. However, an expanding role of magnetic resonance imaging is evident.