Paget's Disease of Bone
A chronic bone disorder where normal bone turnover is accelerated and disorganised, leading to enlarged, weakened bones prone to deformity and fracture. Calcitonin-salmon was historically used for Paget's disease before being largely replaced by bisphosphonates.
Technical Context
Paget's disease involves: excessive osteoclastic bone resorption → reactive excessive osteoblastic bone formation → disorganised woven bone (larger, weaker, more vascular than normal lamellar bone). Prevalence: 1-3% of adults >55 years (decreasing), often asymptomatic. Diagnosis: elevated serum alkaline phosphatase + characteristic radiographic findings (bone expansion, cortical thickening, sclerotic/lytic areas). Symptoms: bone pain, deformity (bowed tibiae, enlarged skull), fractures, hearing loss (temporal bone involvement), and rarely malignant transformation (osteosarcoma, <1%). Treatment: bisphosphonates (zoledronic acid single IV dose — now first-line). Calcitonin-salmon was a historical treatment (SC injection for 6-18 months) — it suppresses osteoclast activity and reduces alkaline phosphatase, but has been largely replaced by bisphosphonates which produce more complete and durable biochemical remission.