Osteochondromatosis (HMOCE - Hereditary Multiple Osteo- Cartilagenous Exostoses - HME - Hereditary Multiple Exostoses)

HMOCE is a rare, autosomal dominant condition where an genetic error of bone growth results in the formation of multiple osteochondromas. The condition can range from a mild nuisance to a very severe, disabling, and even poentially deadly problem depending on the number and location of the lesions.

See basic information on osteochondromas here. See a clinical case of HMOCE here.

HMOCE is an autosomal dominant condition. The condition is genetically heterogeneous and it has been linked to three loci including 8q24.1 (EXT1), 11p11-12 (EXT2), and 19p (EXT3). EXT1 and EXT2 are proposed tumor supressor genes which may be lost in HMOCE, resulting in the growth of the lesions.

The condition can lead to both sessile and pedunculated lesions. The lesions may occur on different bones or on the same bone, and symptoms present in the first decade of life. There may be a few lesions, dozens, or hundreds. Patients may have short stature, limb-length discrepancies, valgus angulation of the knee and ankle, bowing of the radius with ulnar deviation of the wrist, and subluxation of the radiocapitellar joint. Joints adjacent to paired bones, such as the knee, ankle, and wrist, are affected by differential growth of the two involved bones which leads to angular deformities. The lesions cluster at the metaphyseal ends of the bones near the joint and may lead to loss of motion, hip dysplasia, joint subluxation, nerve compression, vascular pseudo-aneurysm, cord compression, and pain.

The risk of malignant transformation to chondrosarcoma in hereditary multiple osteochondromatosis is unknown, but may be 25-30% compared to approximately 1% for a solitary osteochondromas. The risk of malignant degeneration increases as the number and size of the osteochondromas increases. In general, a sessile lesion is more likely to degenerate into sarcoma than an exostosis. Cancer risk assessment should be performed by an orthopedic oncologist. The authors of this site pay particular attention to the large deep osteochondromas, often located on the pelvis or the spine, where malignant transformation may be more likely and much more difficult to treat.

Surgical removal of troublesome lesions or lesions which appear to possess malignant potential is associated with a good outcome. Significant angular deformities of the lower limb can be reduced or eliminated with re-alignment procedures, which should improve function and reduce pain. Early surgical corrections of deformities of the forearm has been advocated to improve function. However, the actual functional improvement has been questioned, and surgery may be safely delayed until after skeletal maturity. Complications occur in approximately 10-12% of cases following elective excision of osteochondromas, including nerve injury, arterial laceration, and fracture. For this reason, the lesions should not be removed just because they exist. Indications for surgical removal include persistant pain, functional impairment, joint subluxation, neuropraxia, and others.

The authors of this site recommend that patients with this disorder be evaluated by an orthopedic oncologist. An initial comprehensive evaluation is done, followed by regular scheduled follow-up exams as well as investigation of new problems or symptoms. In this way, necessary and helpful treatments are pursued and useless or dangerous procedures are avoided. Cancer risk can be assessed on an ongoing basis. The lifetime exposure to radiation for scans, radionucleotide studies, and surgical procedures needs to be managed to avoid secondary risks. Family members may need to be screened for orthopedic problems and cancer risk.

10/14/05 HD3

References:

Bridge, JA et al: Cancer. 1998 May 1;82(9):1657-63

Wirganowicz, PZ Journal of Pediatric Orthopedics. 17(4):455-459, July/August 1997

Steiber and Dormans, J Am Acad Orthop Surg. 2005 Mar-Apr;13(2):110-20

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