Hereditary multiple exostoses (HME), also known as diaphyseal aclasis, is a rare genetic disorder characterized by multiple bony growths (exostoses) on the long bones. These exostoses are covered in cartilage and usually grow until after puberty, sometimes causing deformities or limiting movement. While the exostoses are generally benign, rare malignant transformation can occur in 1% of cases. Treatment may include surgical removal of symptomatic exostoses to relieve pain or correct deformities.

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Diaphyseal Aclasis
Definition
Hereditary multiple exostoses,
Also known as..
Diaphyseal Aclasis
External Chondromatosis Syndrome
Multiple Cartilaginous Exostoses
Multiple Exostoses
Multiple Exostoses Syndrome
Multiple Osteochondromatosis
Radiographic Appearance
Due to the widespread nature of the disease a limited skeletal survey may need to be
performed with additional modalities eg CT of areas with severe symptoms.
Pathology
Hereditary Multiple Exostoses (HME) is a rare skeletal disorder that is inherited in an
autosomal dominant fashion. As the name suggests, this disorder is characterized by multiple
bony growths or tumors (exostoses), often on the growing end (epiphysis) of the long bones
of the legs, arms, and digits. These bony growths are covered by cartilage and usually
continue to grow until shortly after puberty. They may cause deformities, especially of the
ankle, knee, and wrist
Although any bone can be affected, the long bones (legs, arms, fingers, toes), pelvis and
shoulder blades are the most common, while the face and skull are generally unaffected.
Boys and girls can both be affected. Older literature claimed that boys were more severely
troubled by MHE, but bigger series of patients studied recently do not support this theory
MHE can be troublesome. Because the exostoses grow near the growth centers of the bone,
they can make the growth center grow poorly, or only part of it grow poorly. This makes a lot
of people with MHE somewhat shorter than average or have bowed arms or legs. Often, the
forearm will bow out toward the lime finger, or the legs can become knock kneed. This is
frequently concerning, but function is often normal though cosmetically, the bowing can be
very troubling. Sometimes folks with MHE get stiff, especially in the elbows and hips,
usually because their exostoses block some of their motion. While children are growing,
exostoses can be painful. They seem to be very sensitive to getting bumped. Kids often
develop exostoses on the inside of their knees and these can hit together when they run,
which hurts!
Sometimes exostoses grow near nerves or tendons and press on them. In these cases, they
often need to be removed so they won't damage the structure laying over them.
The most frightening complication of MHE is also one of the most uncommon. Rarely (less
than 1% of the time), the benign exostoses of MHE can become a malignant tumor called
chondrosarcoma. This happens almost always after adulthood when skeletal growth has
ceased. Usually, patients who develop chondrosarcoma are in their 20's to 50's. If a person
with MHE notices that an exostoses is getting bigger or painful after they have stopped
growing they should get to their doctor! Growth and pain are two important warning signs
that a benign tumor has become malignant. Chondrosarcoma is very rare, but it is something
MHE families must know about
Treatment:
Some people with MHE never require any treatment. They learn to compensate for deformity
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or decreased range of motion so they function normally. When deformity does occur, it often
happens so slowly that the patient can compensate for it well, while others may require
surgery to help them.
If an exostoses is painful, pressing on an important structure, cosmetically unattractive or if
easily bumped, it can be surgically removed. Once removed, exostoses can reoccur (about 20
- 50% of the time), but may not regrow to a size large enough to be symptomatic. Removal
itself is usually a fairly small procedure; some are removed without ever staying overnight in
the hospital.
If an exostoses causes a growth abnormality, like bowing, sometimes just removing the
exostoses early enough will allow the bone to straighten itself out and remodel as the child
grows. Some bowing is so severe that not only must the exostoses be removed, but also the
bone must be straightened. This can be done by either cutting the bone, straightening it and
then holding it in place while it heals or if the child is still growing by changing the rate of
growth on one side of the growth plate. Currently there are several options and your doctor
should be able to explain them to you.
If an exostoses does become malignant and turn into a chondrosarcoma then it must be
removed. A specialist in orthopedics and bone tumors would be required to help with this.
Images
http://www.rad.washington.edu
Useful Link: http://members.tripod.com/MOONROSE_22/
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