Long bones may develop pathological fractures. Serum calcium and phosphorus are normal. Alkaline phosphatase is markedly elevated. Urinary excretion of hydroxyproline is elevated. Histologically, there is intense osteoclastic resorption of normal bone by giant multinucleated cells.
Osteoblasts produce exuberant hypervascular new bone.
There is distortion and disruption of the organized bony matrix. As the lesion are asymptomatic, imaging is fortuitous. It has not been convincingly demonstrated whether this is a hypervascular pagetic bone, or the osteoblastic reaction of normal bone in response to the adjacent abnormal and expanding matrix. Early Paget's disease manifesting both osteoporosis circumscripta and destructive lesions by both bone scanning and radiographs. Bone scanning in osteolytic Paget's disease.