A 22-year-old woman presents with multiple bony lumps over both knees, shoulders, and pelvis that have been present since childhood and continue to grow slowly. Family history is significant for similar bony tumors in her mother and maternal grandfather. Plain radiographs show multiple sessile and pedunculated bony projections with cartilage caps at the metaphyseal regions of long bones. Genetic testing reveals a mutation in the EXT1 gene. What is the most appropriate management for this patient?

Explanation

## Diagnosis: Hereditary Multiple Osteochondromas (HME/EXT) ### Clinical Presentation **Key Point:** Hereditary multiple osteochondromas (HME), also called hereditary multiple exostoses (HME/EXT), is an autosomal dominant condition characterized by multiple osteochondromas arising from mutations in EXT1 or EXT2 genes. The patient's family history and genetic confirmation establish this diagnosis. ### Genetic Basis | Gene | Frequency | Chromosome | Function | |------|-----------|-----------|----------| | **EXT1** | 70–80% of HME cases | 8q24.11 | Encodes exostosin-1 (glycosyltransferase) | | **EXT2** | 10–20% of HME cases | 11p11.2 | Encodes exostosin-2 (glycosyltransferase) | | **Sporadic mutation** | ~10% of cases | — | De novo mutations | **High-Yield:** Loss of EXT1/EXT2 function impairs heparan sulfate synthesis, leading to dysregulation of bone morphogenetic protein (BMP) signaling and uncontrolled cartilage proliferation at the growth plate. ### Clinical Features of HME - **Multiple osteochondromas** — typically 10–200+ lesions - **Onset** — childhood to adolescence - **Growth pattern** — lesions grow with the skeleton; growth slows or stops at skeletal maturity - **Locations** — metaphyseal regions of long bones (femur, tibia, humerus, pelvis, ribs) - **Complications** — limb length discrepancy, angular deformities, nerve/vessel compression, functional impairment - **Malignant transformation risk** — 5–10% (vs. <1% for solitary osteochondromas) ### Management Strategy ```mermaid flowchart TD A[HME/EXT Diagnosis Confirmed]:::outcome --> B{Lesion Symptomatic or<br/>Concerning Features?}:::decision B -->|No| C[Observation with Annual<br/>Clinical & Imaging Assessment]:::action B -->|Yes| D{Signs of Malignant<br/>Transformation?}:::decision D -->|No| E[Surgical Excision for<br/>Symptom Relief]:::action D -->|Yes| F[Urgent Surgical Excision<br/>+ Oncology Consultation]:::urgent C --> G[Continue Surveillance<br/>Until Skeletal Maturity]:::action G --> H[Reduce Frequency Post-Maturity]:::action E --> H ``` ### Surveillance Protocol **Key Point:** The standard approach is **conservative management with surveillance**, NOT prophylactic excision of all lesions. 1. **Clinical examination** — annually, assess for new lesions, size changes, functional impairment, nerve/vessel compression 2. **Imaging** — plain radiographs annually; MRI if: - Rapid growth (especially after skeletal maturity) - Cartilage cap >3 cm - Pain or neurological symptoms - Concern for malignant transformation 3. **Surgical excision** — indicated only if: - Symptomatic (pain, functional impairment) - Mechanical irritation (bursa, tendon, nerve, vessel) - Evidence of malignant transformation (chondrosarcoma) - Cosmetic concern (patient preference) ### Red Flags for Malignant Transformation **Warning:** Chondrosarcoma develops in 5–10% of HME patients. Suspect malignant transformation if: - **Rapid growth** after skeletal maturity (when lesions should be stable) - **New onset pain** in a previously asymptomatic lesion - **Cartilage cap >3 cm** on imaging - **Cortical thickening** or endosteal scalloping - **Soft tissue mass** on CT/MRI - **Elevated alkaline phosphatase** (nonspecific but concerning) ### Clinical Pearl **High-Yield:** Prophylactic excision of all osteochondromas in HME is NOT recommended because: 1. Most lesions remain asymptomatic 2. Surgical morbidity (nerve/vessel injury, recurrence) must be weighed against benefit 3. Malignant transformation risk, while higher than solitary lesions, is still <10% 4. Lesions typically stabilize after skeletal maturity 5. Surveillance is cost-effective and safe ### Chemotherapy & Bisphosphonates **Warning:** Neither chemotherapy nor bisphosphonates are indicated for HME. These are benign lesions (even with malignant potential) and do not respond to systemic therapy. Bisphosphonates inhibit osteoclasts and promote bone formation, which would worsen the problem. [cite:Rockwood & Green's Fractures in Adults Ch 32; Orthopedic Surgery Principles & Practice 2e Ch 52]