a disorder of unknown cause characterized by excessive bone fomation at skeletal sites subject to normal or abnormal stresses, generally where tendons and ligaments attach to bone. The spine is the predominant site of involvement, although extraspinal sites may also be affected. Some patients may develop ossification after surgery or in response to coexistent diseases, such as rheumatoid arthritis. This disease is also known by other names, including spondylitis ossificans ligamentosa, spondylosis hyperostotica, senile ankylosing hyperostosis of the spine, Forestier's disease, spondylosis deformans and vertebral osteophytosis.
Three criteria are required to diagnosis spinal involvement in DISH:
flowing calcification and ossification along the anterolateral aspect of at least four contiguous vertebral bodies with or without pointed excrescences; relative preservation of intervertebral disc height and absence of extensive changes typical of degenerative disc disease; and absence of bone ankylosis of the apophyseal joints or of erosion, sclerosis, or intra-articular osseous fusion of the sacroiliac joints.Radiographic abnormalities of DISH are observed most commonly in the thoracic spine (Fig.1). Calcification and ossification may lead to the presence of a radiodense shield in front of the vertebral column. Generally the spine develops an irregular and bumpy contour, although occasionally a smooth pseudospondylitic pattern of ossification may be seen. In the cervical spine cortical hyperostosis is the earliest finding and, gradually, elongated bony outgrowths appear at the anterior margins of the vertebrae. Abnormalities occur in the lumbar spine almost as frequently as in the thoracic spine. Extraspinal abnormalities are typically bilateral and symmetrical pelvic changes consist of bone proliferation or "whiskering," calcification and ossification of ligaments, and para-articular osteophytes. Enthesophytes are frequently seen on the posterior and inferior surfaces of the calcaneus and on the dorsal surface of the talus, dorsal and medial regions of the tarsal navicular bone, posterior surface of the ulnar olecranon, and lateral and plantar aspects of the cuboid and base of the fifth metatarsal bone. In the knee, ligamentous ossification occurs within the quadriceps mechanism with anterior patellar hyperostosis and irregularities of the tibial tuberosity. Enthesophytes also are frequent in the elbow and may be of considerable size.
Excessive heterotopic ossification is sometimes seen after hip or knee surgery in some patients with DISH, supporting the view that the disorder may represent a bone-forming diathesis.
Rheumatoid arthritis and DISH (RA/DISH) can coexist in the same patient, in which case the radiographic abnormalities of rheumatoid arthritis may be modified (absence of osteoporosis and the presence of bone sclerosis and proliferation about erosions, osteophytes, and intra-articular bony ankylosis).
Ossification of the posterior longitudinal ligament also occurs with increased frequency in patients with DISH, as does compromise of the cervical cord as a result of hyperostosis or ossification of spinal ligaments. Similarly, acute fracture and pseudarthrosis of the spine may accompany this disorder.
