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The term “spondyloarthritis” is used to describe an overlapping group of diseases that are characterized by inflammation of the sacroiliac joints (sacroiliitis); axial spine (spondylitis); tendon, fascia, and ligament insertion sites (enthesitis); and, in some patients, an oligoarthritis, rash, or inflammatory eye disease (uveitis). This group of diseases has also been referred to as seronegative spondyloarthritis based on the absence of rheumatoid factor. These diseases include ankylosing spondylitis, psoriatic arthritis, the arthritis of inflammatory bowel disease, and reactive arthritis. Although these conditions share common features, each one has distinct clinical and epidemiologic characteristics (Table 17–1). However, in some patients, especially early in the disease presentation, the diagnosis is not clear; these patients are considered to have undifferentiated spondyloarthritis. The overall prevalence of these conditions has been estimated to be between 0.5% and 1.5%.
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The entheses are an important site of inflammation and subsequent pathology in spondyloarthritis. These are locations where tendons, fascia, and ligaments insert into bone. Clinical manifestations include heel pain with involvement of the Achilles tendon, foot pain at the site of insertion of the plantar aponeurosis, or swelling of an entire digit (dactylitis or sausage digit) due to inflammation of the flexor and extensor tendons of the fingers or toes.
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Histologically, the synovial inflammation in spondyloarthritis is characterized by chronic inflammatory infiltrates that are nonspecific and indistinguishable from that of rheumatoid arthritis. While erosive bone disease does occur, unlike the rheumatoid process, this inflammatory process is also accompanied by new bone formation across previous articulations. This ossification of the articular and ligamentous structures of the spine leads to syndesmophyte formation and may result in eventual fusion and characteristic radiographic findings.
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The dominant clinical problems that bring the patient with spondyloarthritis to a clinician and require careful management over many years are axial pain, limitation of motion, and deformity of the spine. In all forms of spondyloarthritis, the same principles of diagnosis and management of the axial problem apply ...