Multiple osteochondromas

Multiple osteochondromas (MO), also known as hereditary multiple exostoses (HME) or diaphyseal aclasis, is a genetic skeletal disorder characterized by the development of multiple benign cartilage-capped bone tumors (osteochondromas) that grow outward from the surfaces of bones, particularly near the growth plates of long bones. The condition primarily affects the skeletal system, with osteochondromas most commonly arising on the long bones of the limbs (femur, tibia, fibula, humerus, radius, and ulna), as well as the pelvis, scapula, and ribs. The growths typically become apparent in childhood and continue to develop until skeletal maturity. Key clinical features include palpable bony lumps near joints, skeletal deformities such as shortening of the forearm with bowing of the radius, valgus deformity of the knee and ankle, limb-length discrepancy, short stature, restricted range of motion, and chronic pain. Compression of adjacent nerves, blood vessels, or tendons by the osteochondromas can cause additional complications. One of the most significant concerns is the risk of malignant transformation of an osteochondroma into a secondary peripheral chondrosarcoma, estimated to occur in approximately 2–5% of affected individuals, typically in adulthood. Multiple osteochondromas is caused by loss-of-function mutations in the EXT1 gene (chromosome 8q24.11) or the EXT2 gene (chromosome 11p11.2), both of which encode glycosyltransferases involved in heparan sulfate biosynthesis. Mutations in EXT1 account for approximately 60–70% of cases and are generally associated with a more severe phenotype. There is currently no cure for the condition. Treatment is primarily surgical and is directed at removing symptomatic osteochondromas that cause pain, functional impairment, nerve or vascular compression, or cosmetic concerns. Orthopedic interventions may also be needed to correct skeletal deformities and limb-length discrepancies. Lifelong surveillance is recommended to monitor for malignant transformation, with attention to any rapid growth of a lesion, new onset of pain, or changes in imaging characteristics in adulthood.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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