Ankylosing hyperostosis

Diffuse idiopathic skeletal hyperostosis (DISH) is a condition characterized by abnormal calcification/bone formation ('hyperostosis') of the soft tissues surrounding the joints of the spine, and also the peripheral or appendicular skeleton. In the spine, there is bone formation along the anterior longitudinal ligament and sometimes the posterior longitudinal ligament, which may lead to partial or complete fusion of adjacent spinal levels. The facet and sacroiliac joints tend to be uninvolved. The thoracic spine is the most common level involved. In the peripheral skeleton, DISH manifests as a calcific enthesopathy, with pathologic bone formation at sites where ligaments and tendons attach to bone. The majority of people with DISH are not symptomatic, and the findings are an incidental imaging abnormality. In some, the x-ray findings may correspond to symptoms of back stiffness with flexion/extension or with mild back pain. Back pain or stiffness may be worse in the morning. Rarely, large anterior cervical spine osteophyte may affect the esophagus or the larynx and cause pain, difficulty swallowing or even dysnea. Similar calcification and ossification may be seen at peripheral entheseal sites, including the shoulder, iliac crest, ischial tuberosity, trochanters of the hip, tibial tuberosities, patellae, and bones of the hands and/or feet. The exact cause is unknown. Mechanical, dietary factors and use of some medications (e.g. isotretinoin, etretinate, acitretin and other vitamin A derivatives) may be of significance. There is a correlation between these factors but not a cause or effect. The distinctive radiological feature of DISH is the continuous linear calcification along the antero-medial aspect of the thoracic spine. DISH is usually found in people in their 60s and above, and is extremely rare in people in their 30s and 40s. The disease can spread to any joint of the body, affecting the neck, shoulders, ribs, hips, pelvis, knees, ankles, and hands. The disease is not fatal, however some associated complications can lead to death. Complications include paralysis, dysphagia (difficulty swallowing), and lung infections. Although DISH manifests in a similar manner to ankylosing spondylitis, they are separate diseases. Ankylosing spondylitis is a genetic disease with identifiable marks, tends to start showing signs in adolescence or young adulthood, is more likely to affect the lumbar spine, and affects organs. DISH has no indication of a genetic link, and does not affect organs other than the lungs, which is only indirect due to the fusion of the rib cage. Long term treatment of acne with vitamin derived retinoids, such as etretinate and acitretin, have been associated with extraspinal hyperostosis. DISH is diagnosed by findings on x-ray studies. Radiographs of the spine will show abnormal bone formation (ossification) along the anterior spinal ligament. The disc spaces, facet and sacroiliac joints remain unaffected. Diagnosis requires confluent ossification of at least four contiguous vertebral bodies. Classically, advanced disease may have 'melted candle wax' appearance along the spine on radiographic studies. In some cases, DISH may be manifested as ossification of enthesis in other parts of the skeleton. The calcification and ossification is most common on the right side of the spine. In people with dextrocardia and situs inversus this calcification occurs on the left side.