Skeletal remodelling and bone related hormones in two adults with increased bone mass

This study of two cases documents increased bone mass in a 30-yr-old man and osteopetrosis in a 38-yr-old woman and examines the patients in terms of radiologic features, bone photon absorptiometry and bone biopsy analyses which include tetracycline kinetics. Both patients had elevated bone mass based on quantitative bone histology of iliac crest biopsies normal, or low PTH, and normal calcitonin values. However, they differed markedly from each other in other respects: One patient possessed significantly increased rates of bone formation and mineralization, had elevated serum alkaline phosphatase, increased total hydroxyproline over a 24 hour urine collection but displayed a normal amount of bone surface involved in resorption. The other subject had normal bone formation parameters, but had elevated serum acid phosphatase and a significantly elevated resorbing (crenated) surface. Although most theories ascribe the cause of osteopetrosis to decreased resorption, our study shows that increased bone formation, even when accompanied by normal resorption, can lead to the abnormal accumulation of bone mass. In this respect, the resorptive response of this patient was abnormal; the normal coupled relationship between bone formation and bone resorption, which ensures proper control of endosteal bone volume, had been lost.