Tumor biology and incidence

  • Disease of bone with uncertain etiology (although slow virus may be cause)
  • 1-3% of individuals in US over age 45 have Paget’s disease
  • Usually polyostotic; involves cortical and cancellous bone
  • Three phases of the disease
    • Osteoclastic (reportive)
      • Active resorption of bone by osteoclasts
      • Endosteal erosion leading to expansion of the bone and subperiosteal new bone formation
      • Increased urinary excretion of collagen degradation products (eg, hydroxyproline)
    • Osteoblastic (sclerotic)
      • Compensatory new bone formation by osteoblasts
      • Increase in serum alkaline phosphatase levels
    • "Burn out"
      • Marked decline in osteoclastic and osteoblastic activity

Presentation

  • Most patients asymptomatic
  • Those who are symptomatic complain of bone and joint pain
  • Compression of neural structures possible
  • Pathologic fractures possible

Physical findings

  • Often diagnosed incidentally during radiographic investigation of other conditions.
  • May have gross bony deformity; may be only physical finding
  • Rapid onset of pain and swelling suggests malignant degeneration (rare; less than 1% chance of malignant degeneration, usually to osteosarcoma)

Radiographic appearance

Osteoclastic phase
  • Lytic lesions in bone; thinning of trabeculae
  • Skull may show zone of rarefied bone (osteoporosis circumscripta)
  • In long bones, lysis advances in V- or flame-shaped cutting cone
  • Cortices may be rarefied; risk of pathologic fracture
Osteoblastic phase
  • Deposition of new bone outpaces bone resorption
  • New bone is woven bone; laid down along stress lines
  • Thickening of trabeculae along stress lines is radiographically characteristic of Paget’s
  • Evidence of lysis also present
  • New bone formation in skull may have a "cotton wool" appearance.
  • May see thickening of bony trabeculae, widening of cortices, and subperiosteal new bone formation, as well as bony enlargement
  • Blastic changes in vertebral bodies of spine may have classic "ivory vertebrae’ or "picture frame vertebrae" appearance
“Burn out” phase
  • Lytic and blastic appearance of bones
  • May see fractures in long bones affected by disease

Diagnosis and treatment

  • Control osteoclastic activity
    • Diphosphonates
    • Calcitonin
    • Methotrexate