Diffuse idiopathic skeletal hyperostosis (DISH) is a spondyloarthropathy

Spondyloarthropathy

Spondyloarthropathy is any joint disease of the vertebral column. Spondyloarthropathy with inflammation is called spondylarthritis. In contrast, spondylopathy is a disease of the vertebra itself, but many conditions involve both spondylopathy and spondyloarthropathy...

 also known as Forestier's disease and ankylosing Hyperostosis.
It is a noninflammatory disease, with the principal manifestation being calcification and ossification of spinal ligaments and the regions where tendons and ligaments attach to bone (entheses). the most common abnormality is bilateral calcification seen on both side of the thoracic spine

Etiology

The exact cause is unknown. Mechanical factors, dietary and long term use of some antidepressants may be of significance. There is a correlation between these factors but NOT a cause or affect. It also is a cause of "bamboo spine," a fusion of the vertebral column causing the spine to curve forward. The distinctive radiological feature of DISH is the continuous linear calcification along the antero-medial aspect of the thoracic spine. the disease is usually found in people in their 60's and up and is extremely rare in people in their 40's and 30's. the disease can spread to any joint of the body affecting neck, shoulders, ribs, hips, pelvis, knees, ankles , hands. the disease is not fatal , how ever some of the complications due to the progression can be. Complications are as follows, paralysis , disphagia (the inability to swallow), and pulmonary infections. although Forestier's disease acts extremely similarly to that of ankylosing spondylitis, these two are totally separate diseases. A.S is a genetic disease with identifiable marks, and affects organs. Forestier's disease has no indication of a genetic link, and does not affect organs other than the lungs which is only indirectly due to the fusion of the rib cage.
information was gathered from DR. DANIAL SCIUBBA ,Neurology dept. at Johns Hopkins hospital, DR. ANTHONY REGINATO, rheumatologist from Mass General HOSPITAL. DR DE ASLA also at MASS GENERAL HOSPITAL. other links are wrongdiagnoses.com. NIH, NORD.

Forestier, J., Lagier, R.; Ankylosing hyperostosis of the spine. Clin. Orthop. 1971; 74:65
Treatment of acne with vitamin derived retinoids was noticed to be associated with similar manifestations in some patients especially with Etretinate

Etretinate

Etretinate is a medication developed by Hoffmann–La Roche that was approved by the FDA in 1986 to treat severe psoriasis...

  which is no longer available for clinical use. other retinoids, like acitretin

Acitretin

Acitretin is a second generation retinoid. It is taken orally, and is typically used for psoriasis....

may cause extraspinal hyperostosis.

Symptoms

It can be present as a radiological abnormality, mentioned above, without any symptoms. The usual complaint is with thoracic spine pain. This occurs in around 80% of patients. Morning stiffness is also noticed in almost two thirds of patients. increased incidence of dysphagia is also reported in some series of cases.
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.

Treatment

As areas of the spine and tendons can become inflamed NSAIDs such as ibuprofen and Naproxen can be helpful in both relieving pain and inflammation of DISH. It is hoped that by minimizing inflammation in these areas, further calcification of tendons and ligaments of the spine leading to calcific bony outgrowths (osteophytes) will be prevented. Physiotherapy to increase the spines range of motion may be beneficial.