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Paget's disease (formerly known as osteitis deformans) Bone tumours such as osteosarcoma, chondrosarcoma, fibrosarcoma, giant cell tumours and secondary metastases are more common in Pagetic lesionsRadiologically, early osteolytic lesions are visible in the skull (oval-round lesions termed osteoporosis circumscripta) and long bones (lesions begin at the metaphysis and grow at 1cm/year if untreated). Later, osteosclerotic lesions occur and bone becomes chaotic and thickened, with bowing and fracturesBiochemically, there is an elevated serum alkaline phosphatase (from osteoblast membranes) which correlates to the degree of skeletal involvement, as does the 24 hour urinary excretion of pyridinoline cross-links (an index of bone matrix collagen resorption). Hypercalciuria and hypercalcaemia are rare due to tight metabolic coupling of bone resorption and formation
