Updated: 6/17/2021

Oncogenic Osteomalacia

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  • summary
    • Oncogenic Osteomalacia is a paraneoplastic syndrome of renal phosphate wasting caused by a bone or soft tissue tumor. Patients may present with osteopenia and pathologic fractures.
    • Diagnosis is made with PET/SPECT scans to identify the location of the tumor. 
    • Treatment involves identifying and resecting the tumor. 
  • Epidemiology
    • Demographics
      • age bracket
        • age of onset is late childhood to early adulthood
  • Etiology
    • Pathophysiology
      • the tumor secretes a humoral factor ("phosphatonin") that affects the proximal renal tubules
      • reduces calcitriol production in the kidney and inhibits phosphate transport
      • leads to increased renal phosphate excretion, hypophosphatemia and osteomalacia
      • types of tumors that cause oncologic osteomalacia (known as phosphaturic mesenchymal tumor)
        • benign tumors (more common)
          • phosphaturic mesenchymal tumors (mixed connective tissue variant) e.g. hemangiopericytoma (commonest cause)
          • osteoblastoma-like tumors
          • ossifying fibrous tumors
          • nonossifying fibrous tumors
        • malignant causes (rare)
          • osteosarcoma
          • fibrosarcoma
    • Genetics
      • mutations
        • phosphatonin gene is FGF23
    • Associated conditions
      • orthopaedic manifestations
        • pathological fractures of long bones and vertebrae
  • Presentation
    • Symptoms
      • generalized bone and muscle pain
      • fractures of long bones, ribs and vertebrae
      • proximal muscle weakness
      • fatigue
  • Imaging
    • Radiographs
      • findings
        • diffuse osteopenia
        • Looser's zones (pseudofractures)
    • Octrotide scans (radiolabeled somatostatin analog)
      • gallium-68 DOTA-octreotate PET scan
      • indium-111 pentetreotide SPECT/CT
      • indications
        • to identify primary tumors when TIO is suspected
        • will only identify tumors expressing somatostatin receptors
  • Studies
      • Lab Values
      • Serum Ca
      • Serum P
      • Alk phos
      • PTH
      • 25-(OH)vit D
      • 1,25-(OH)vit D
      • Urinary Ca
      • Osteomalacia
      • Low
      • Low
      • High
      • High
      • Low
      • Low
      • Low
      • Osteoporosis
      • Normal
      • Normal
      • Variable
      • Normal
      • Normal
      • Normal
      • Normal
      • Tumor induced osteomalacia
      • Low
      • Very low
      • Low
      • Low
      • Low
      • Low
      • Low
      • Osteopetrosis
      • Normal
      • High
      • Normal
      • Normal
      • Normal
      • Normal
      • Normal
  • Treatment
    • Nonoperative
      • phosphate supplementation with 1,25-dihydroxyvitamin D
    • Operative
      • tumor removal
        • outcomes
          • resolution of hypophosphatemia and low vitamin D levels within hours of resection
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