METABOLIC OBSERVATIONS IN A CASE OF THYROTOXICOSIS WITH HYPERCALCEMIA*

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Abstract
Hyperthyroidism characteristically causes excessive urinary and fecal excretion of calcium and, rarely, hypercalcemia. These abnormalities were studied in a 58-year-old thyrotoxic male. The investigation consisted of a 125-day balance study as the patient became euthyroid and a similar 50-day balance study during a recurrence of the thyrotoxicosis. The excessive urinary and fecal loss of calcium bore little relationship to the calcium or caloric content of the diet or to the level of nitrogen balance. A high phosphate diet ameliorated the metabolic abnormality and corrected the hypercalcemia. Successful treatment of the thyrotoxicosis produced similar changes in calcium metabolism. Hypercalcemia was not present during recurrence of the thyrotoxicosis. The metabolic observations in this case and those previously reported strongly suggest that the excessive urinary and fecal excretion of calcium in thyrotoxicosis is due to a direct effect of thyroid hormone on osseous metabolism. The hypercalcemia is probably secondary to a disorder in the homeostatic mechanism(s) regulating the content of ionized calcium in the extracellular fluid.