Hereditary multiple exostoses (HME or MHE), also known as Diaphyseal aclasis, is a rare medical condition in which multiple bony spurs or lumps (also known as exostoses, or osteochondromas) develop on the bones of a child. HME is synonymous with Multiple hereditary exostoses and Multiple osteochondromatosis, which is the preferred term used by the World Health Organization.
- Bone lumps
- Bowed arms
- Bowed legs
- Short stature
- Impaired range of joint motion
HMO is caused by mutations in the EXT1 and EXT2 genes. It is inherited in an autosomal dominant pattern, which means that one copy of the altered gene in each cell is sufficient to cause this condition. In most cases, an affected individual inherits the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the condition in their family.
Most affected individuals (96%) that have inherited a gene mutation from their parent show signs and symptoms of this condition. However, the family history may appear negative because of the failure to recognize the disorder in family members and/or reduced penetrance. Reports have suggested that some females may not show clinical features of HMO but still have the gene mutation that causes this condition.
Diagnosis is mostly clinical and radiological. Technetium skeletal scintigrams are occasionally used to determine number of exostoses.
Prognosis and long-term survival can vary greatly from person to person. Generally, the prognosis for a person with HMO is favorable. Most often, osteochondromas stop growing at skeletal maturity.Most individuals with HMO have at least one surgery and many have multiple surgeries. Painful osteochondromas that do not affect the surrounding bone can simply be removed. Complete removal can help to avoid recurrence of the tumor and abnormal bone growth. Osteochondromas that affect the surrounding bone, tissues, and/or nerves may be more difficult to remove and the outcome of surgery depends on the extent of the disease, the size and location of the tumor, and the tumor’s response to therapy. If an osteochondroma becomes a cancerous tumor (osteosarcoma), the outcome is also less certain. Prompt medical attention and aggressive therapy are important for the best prognosis. Continuous follow-up care is essential for a person diagnosed with multiple osteochondromas.
Although the estimated risk of malignant transformation in HME has varied within studies, the majority of researchers agree the lifetime risk is between 1-2%.
The average age for a malignant transformation to occur is between 28-35 years old. Malignant transformation is very rare in children, but the risk increases with age, especially after the age of 30.
Surgical excision is performed when exostoses lead to growth disturbances or lead to disability. Knee osteotomies are associated with high incidence of peroneal nerve paralysis.
Surgery, physical therapy and pain management are currently the only options available to HME patients, but success varies from patient to patient and many struggle with pain, fatigue and mobility problems throughout their lives. It is not uncommon for HME patients to undergo numerous surgical procedures throughout their lives to remove painful or deforming exostoses, correct limb length discrepancies or improve range of motion. Usually the treatment can be problematic. The osteochondromas can return in the same places and may be more painful