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
