3.6 - Heterotopic calcification and ossification

Abstract

Heterotopic, also called ectopic, calcification is a condition in which calcium phosphate crystals deposit in sites that are normally not calcified. If the calcification occurs in the form of osseous or osseous-like tissue, the condition is called heterotopic ossification. Ectopic calcification can occur in various tissues. The mechanism is not understood, except when it occurs during hypercalcemia or in the case of urinary stones. In these cases, precipitation occurs because of the supersaturation of the fluid in calcium and phosphate. Local disturbances of nucleators or of inhibitors of calcium phosphate crystal formation have been proposed as possible mechanisms. The cause of heterotopic ossification is unknown. Heterotopic ossification is common after hip operations with implantation of prosthesis, after paraplegia, and after cerebral trauma. Manifestations are numerous, and depend on the localization of the calcium phosphate deposit. In case of heterotopic calcification, the most frequent location is in the walls of blood vessels, especially the arteries. Many therapies have been tried in heterotopic calcification, but none has proven totally successful. In heterotopic ossification, for example, after hip replacement, the treatments most often used are nonsteroidal anti-inflammatory agents and irradiation. Etidronate, the only bisphosphonate investigated so far in ectopic calcification and ossification, appears to be useful for partial prevention of heterotopic ossifications in some instances. However, the effective dose is the same as that inhibiting normal mineralization, which makes its use difficult.