Osteochondromatosis, or multiple hereditary exostoses, is an autosomal dominant disorder consisting of multiple cartilaginous- capped exostoses (osteochondromas) arising from the metaphyses of bones formed from cartilage. Occasionally, a spontaneous mutation leads to the disorder and genes on chromosomes 8, 11, and 19 have been shown to produce the disease. The skull vault, formed from an intramembraneous process, is never involved. The exostoses start growing in infancy and increase in size during puberty, generally stopping once puberty is complete. Most are found around the knees, ankles, and wrists, and shoulders. The exostoses point away from the joint. The inciting factor is not known, but dysplasia at the growth plate starts the disease progression.

The exostoses themselves are usually asymptomatic, but may limit range of motion of the joint. In addition, they may impinge upon nearby structures including nerves and blood vessels. The most worrisome condition associated with multiple hereditary exostoses is sarcomatous degeneration of an osteochondroma. This occurs in 1 to 2 % of patients. The lesions most at risk are those  occurring near the pelvis, scapula, proximal humerus, proximal femur, and spine. 

Forty percent of patients have a small stature. Leg length discrepancy (asymmetric dwarfism) may need surgical correction. Osteochondromas about the ankle may give rise to a ankle valgus deformity, also requiring surgical correction.

REFERENCES

• Horton WA. Advances in the genetics of human chondrodysplasias. Pediatr Radiol. 1997 May;27(5):419-21
• McCormick C, Duncan G, Tufaro F. New perspectives on the molecular basis of hereditary bone tumours. Mol Med Today. 1999 Nov;5(11):481-6.

Click on an image below for additional information:

BACK