Paget's disease is a disease of increased but uncontrolled bone turnover. It is thought to be primarily a disorder of osteoclasts, with excessive osteoclastic resorption followed by increased osteoblastic activity. Paget's disease is common (UK prevalence 5%) but symptomatic in only 1 in 20 patients. The skull, spine/pelvis, and long bones of the lower extremities are most commonly affected.

Predisposing factors

• increasing age
• male sex
• northern latitude
• family history

Clinical features - only 5% of patients are symptomatic

• the stereotypical presentation is an older male with bone pain and an isolated raised ALP
• bone pain (e.g. pelvis, lumbar spine, femur)
• classical, untreated features: bowing of tibia, bossing of skull

Investigations

• bloods
  • raised alkaline phosphatase (ALP)
  • calcium and phosphate are typically normal. Hypercalcaemia may occasionally occur with prolonged immobilisation
• other markers of bone turnover include
  • procollagen type I N-terminal propeptide (PINP)
  • serum C-telopeptide (CTx)
  • urinary N-telopeptide (NTx)
  • urinary hydroxyproline
• x-rays
  • plain radiographs are the first-line investigation and are usually diagnostic
  • osteolysis in early disease → mixed lytic/sclerotic lesions later
  • skull x-ray: thickened vault, osteoporosis circumscripta
• bone scintigraphy
  • increased uptake is seen focally at the sites of active bone lesions

Management

• indications for treatment include
  • bone pain
  • skull or long bone deformity
  • fracture
  • periarticular Paget's
• bisphosphonate (either oral risedronate or IV zoledronate)
• calcitonin is less commonly used now

Complications