Melorheostosis is a rare skeletal abnormality that causes abnormal growth of new bone tissue on top of existing bones. Signs and symptoms typically appear by late childhood or adolescence. Signs and symptoms may include deformity, contracture, chronic pain, stiffness, and limited range of motion. In some cases, the overlying skin and soft tissue may show thickening, shininess, reddening or darkening, linear scleroderma, and/or swelling. The condition typically affects the long bones, and the legs are affected more often than the arms. Sometimes the small bones of the hand or foot are affected, and rarely, bones of the skull or trunk are affected. The condition is sometimes associated with other bone or connective tissue abnormalities. The diagnosis is based on a combination of clinical and radiological features, which are used to distinguish melorheostosis from other bone disorders.
Isolated melorheostosis (with no other associated disorders) is typically sporadic, occurring in people with no family history of the condition. Around half of cases of isolated melorheostosis are due to acquired, somatic mutations in the MAP2K1 gene; these mutations are not inherited from a parent and occur randomly during a person’s lifetime. In the remainder of cases, the cause is not yet known. Somatic mutations in other, unidentified genes may also cause the disorder. Some people with melorheostosis associated with other bone disorders (specifically osteopoikilosis and Buschke–Ollendorff syndrome) have heritable mutations in the LEMD3 gene, but mutations in this gene are not thought to be responsible for isolated melorheostosis.
Management depends on the severity and symptoms in each person and aims to relieve pain, correct deformity, and restore movement. Management options may include medications, physical therapy, occupational therapy, and/or orthopedic surgery. Melorheostosis is not life-threatening, but chronic pain can greatly impact quality of life.
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