Bone changes in hyperthyroidism: interrelationships between bone morphometry, thyroid function and calcium-phosphorus metabolism.

Iliac-crest biopsies were obtained from 40 untreated hyperthyroid patients after double-labelling with tetracycline. Histomorphometric analyses were performed on undecalcified and decalcified bone sections. The morphometric and chemical data were compared with those in normal control groups and the results of the morphometric analyses were related to thyroid function and to chemical quantities of calcium-phosphorus metabolism. The bone turn-over was increased in the hyperthyroid patients with an increase both in bone resorption and bone formation. Serum alkaline phosphphatase was increased and positively correlated to the amount of osteoid and to the extent of tetracycline-labelled surfaces. The osteoclastic resorption was positively and the bone formation inversely correlated to thyroid activity. This might explain the reduced amount of trabecular bone found in hyperthyroidism. The most striking feature was, however, a pronounced increase in osteoclastic activity in cortical bone followed by increased porosity. The osteoclastic resorption in cortical bone was positively correlated to serum concentrations and urinary excretions of calcium and phosphorus. This indicates that increased cortical osteoclastic resorption is mainly responsible for bone mineral mobilisation in hyperthyroidism.