Investigation of bone and mineral metabolism in hyperthyroidism before and after treatment using calcitonin, 47Ca and balance studies

Seventeen normocalcaemic patients with severe hyperthyroidism were examined before therapy was initiated; 9 were re-examined about 1 year later. Studies with 47Ca under balance conditions and with calcitonin demonstrated a high rate of bone resorption in untreated patients. As a result of the increased bone turnover, the reaction to 6 MRC units of porcine calcitonin iv was more marked in the untreated than in the treated patients, or the control group. In contrast to the normal diurnal pattern for PO4, it was found that during fasting the plasma PO4 level increases in the morning in patients with hyperthyroidism. This increase which was not suppressed by the administered dose of calcitonin developed in spite of an elevated urinary PO4 excretion. After treatment, the serum Ca concentration as well as the urinary and faecal Ca excretion was decreased. The Ca balance improved; the rapidly-exchangeable Ca pool returned to normal. The slowly-exchangeable and the total Ca pools, however, remained enlarged. The rate of bone resorption normalized. The accretion rate on the other hand remained elevated. This is attributed to continued enhancement of bone formation to compensate for the previous loss of bony tissue. (author)