Hereditary Multiple Exostoses: Current Insights

Abstract

Hereditary multiple exostoses (HME), also called hereditary multiple osteochondromas, is a rare genetic disorder characterized by multiple osteochondromas that grow near the growth plates of bones such as the ribs, pelvis, vertebrae and especially long bones. The disease presents with various clinical manifestations including chronic pain syndromes, restricted range of motion, limb deformity, short stature, scoliosis and neurovascular alteration. Malignant transformation of exostosis is rarely seen. The disease has no medical treatment and surgery is only recommended in symptomatic exostoses or in cases where a malignant transformation is suspected. HME is mainly caused by mutations and functional loss of the EXT1 and EXT2 genes which encode glycosyltransferases, an enzyme family involved in heparan sulfate (HS) synthesis. However, the peculiar molecular mechanism that leads to the structural changes of the cartilage and to osteochondroma formation is still being studied. Basic science studies have recently shown new insights about altering the molecular and cellular mechanism caused by HS deficiency. Pediatricians, geneticists and orthopedic surgeons play an important role in the study and treatment of this severe pathology. Despite the recent significant advances, we still need novel insights to better specify the role of HS in signal transduction. The purpose of this review was to analyze the most relevant aspects of HME from the literature review, give readers an important tool to understand its clinical features and metabolic-pathogenetic mechanism, and to identify an effective treatment method. We focused on the aspects of the disease related to clinical management and surgical treatment in order to give up-to-date information that could be useful for following best clinical practice.

Keywords: EXT1; EXT2; heparan sulfate synthesis; hereditary multiple exostoses; medical and surgical treatment; osteochondromas.

Figure 1

Brief description of the HME pathogenesis.

Figure 2

T1-weighted axial MRI showing the osteochondroma at the proximal femur with sciatic nerve entrapment (Case #1).

Figure 3

Intraoperative image of the osteochondroma (Case #1).

Figure 4

Resected specimen (Case #1).

Figure 5

T1-weighted axial MRI showing the exostosis in the proximal humerus, complicated with a massive brachial artery pseudoaneurysm following microtrauma (Case #2).

Figure 6

MRI with a STIR sequence showing the pseudoaneurysm after drainage of the hematoma (Case #2).

Figure 7

A TOF MRI sequence showing the brachial artery pseudoaneurysm (Case #2).

Figure 8

Intraoperative photograph showing the brachial artery pseudoaneurysm (Case #2).

Figure 9

Clinical case 2. Pre-operative radiograph. In the yellow circle, the exostosis that had to be removed.

Figure 10

Clinical case 2. Post-operative radiograph.