Synonyms

• Hereditary multiple exostoses
• HME
• familial multiple osteochondromas

Category

Syndrome

Behaviour

Benign

Gender

Both equally

Tissue of Origin

Cartilage

Epidemiology

• Autosomal dominant genetic disorder
• Incidence 1 in 25,000 - 1 in 50,000
• EXT1 and EXT2 gene mutations
• Multiple osteochondromas throughout skeleton
• Malignancy risk 1-5% to chondrosarcoma

Clinical Features

• Multiple bony protuberances (osteochondromas)
• Progressive limb deformities and length discrepancy
• Pain from nerve/vessel compression
• Limb length inequality requiring monitoring

Location

• Long Bones bilaterally and symmetrically
• Femur, tibia, humerus most common
• Multiple lesions by definition

Imaging

• Full-body skeletal survey: baseline
• MRI of lesions: monitor Cartilage cap thickness
• Annual imaging to assess for malignancy
• Monitor for caps >2 cm

Pathology

• Cartilage-capped bony exostoses
• Benign hyaline Cartilage with endochondral ossification

Genetics

• EXT1 mutations (70%)
• EXT2 mutations (30%)
• Autosomal dominant inheritance

Treatment

• Observation of asymptomatic lesions
• Surgical excision if pain, deformity, or concern for malignancy
• Monitor Cartilage cap size

Prognosis

• Benign exostoses
• 1-5% malignancy risk to chondrosarcoma
• Lifetime surveillance required

Key Points

• SYSTEMIC GENETIC Syndrome
• EXT1/2 mutations define HME
• Multiple bilateral osteochondromas pathognomonic
• Monitor Cartilage caps for malignancy risk

Workup - Blood Tests

No routine blood tests

Workup - Local Imaging

• Full-body skeletal survey: baseline
• MRI of symptomatic or central lesions >2 cm cap
• Monitor for malignant transformation signs

Workup - Biopsy

Only if concern for chondrosarcoma

Workup - Staging

Baseline full-body imaging

Workup - Other

• Genetic testing: EXT1/2 sequencing
• Patient education on malignancy risk

Follow-up Summary

• Annual skeletal imaging
• MRI monitoring of lesions with caps >2 cm
• Assess for rapid growth (malignancy sign)
• Genetic counselling for family
• Orthopedic assessment for limb deformity