Treatment Approach for Multiple Hereditary Exostoses (MHE)
The treatment of multiple hereditary exostoses requires lifelong monitoring with whole-body MRI surveillance every 2 years and surgical intervention for symptomatic lesions or those suspected of malignant transformation. 1
Disease Overview
Multiple hereditary exostoses (MHE), also called hereditary multiple osteochondromas, is an autosomal dominant genetic disorder characterized by:
- Multiple benign osteochondromas growing near growth plates of bones
- Primarily caused by mutations in EXT1 (65-70% of cases) or EXT2 (30-35% of cases) genes
- Prevalence of approximately 1/50,000 in North America (varies geographically)
- Near 100% penetrance in males and 96% in females
- Typically diagnosed between 3-5 years of age
Clinical Assessment
Key Clinical Manifestations to Evaluate:
- Pain (most common symptom)
- Restricted joint motion
- Limb deformities and limb length discrepancies
- Short stature
- Angular deformities of long bones
- Scoliosis
- Neurovascular complications
Surveillance Protocol
Imaging Surveillance:
- Baseline imaging: Whole-body MRI at early adolescence (around age 12) when most osteochondromas have evolved 1
- Regular surveillance: Biennial (every 2 years) whole-body MRI for lifelong monitoring 1
- Targeted imaging: Consider more frequent regional MRI (every 2-3 years) for lesions in high-risk locations such as pelvis and scapula, particularly in males or EXT1 mutation carriers 1
Physical Examination:
- Annual physical examinations starting in childhood 1
- Prompt investigation of any osteochondroma with:
- Increasing pain
- Rapid growth
- Size >5-6 cm
- Location in pelvis/scapula
Surgical Management
Surgery is the mainstay of treatment and should be considered in the following situations:
- Symptomatic lesions causing pain
- Lesions restricting joint motion
- Lesions causing neurovascular compression
- Lesions interfering with normal function
- Suspected malignant transformation
Warning Signs for Malignant Transformation:
- Rapid growth of an osteochondroma
- Increasing pain
- Cartilage cap thickness >2.0-3.0 cm on MRI or CT scan 1
Specialized Care Considerations
- Treatment should be centralized in high-volume tumor departments that coordinate screening and treatment interventions 1
- Orthopedic providers should be involved in monitoring osteochondromas 1
- Multidisciplinary approach involving pediatricians, geneticists, and orthopedic surgeons
Malignant Transformation Risk
- Risk of transformation to chondrosarcoma: 0.2-5.9% of individuals 2
- 75% of malignant transformations occur between ages 20-40
- Higher risk in:
- Males
- Individuals with EXT1 mutations
- Lesions in the pelvis or scapula
Important Caveats
- No effective medical treatment exists currently; management is primarily surgical 3, 2
- Experimental medical therapies are under investigation but not yet standard of care 4
- Not all osteochondromas require removal; asymptomatic lesions in non-critical locations can be monitored
- Forearm involvement is common and may require specialized surgical approaches 5
- After skeletal maturity, the risk of new osteochondroma formation decreases, but monitoring for malignant transformation must continue
Follow-up After Surgery
- Continue regular surveillance with whole-body MRI every 2 years even after surgical removal of symptomatic lesions
- Maintain annual clinical examinations to detect new symptomatic lesions
- Educate patients about warning signs that should prompt immediate medical attention
By following this structured approach to treatment and surveillance, the morbidity associated with MHE can be minimized while ensuring early detection of potential malignant transformation.