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What is Diffuse idiopathic skeletal hyperostosis and explain in detail?
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 of 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 vertebrae. 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.

Signs and symptoms
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 osteophytes may affect the esophagus or the larynx and cause pain, difficulty swallowing or even dyspnea. 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.DISH can be a complicating factor when suffering from trauma involving the spine. It increases the risk of unstable fractures involving the intervertebral disc and the calcified/ossified ligaments which influences the need for surgical treatment.

Cause
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