BONE MASS, BONE TURNOVER, CALCIUM HOMEOSTASIS, AND BODY-COMPOSITION IN SURGICALLY AND RADIOIODINE-TREATED FORMER HYPERTHYROID PATIENTS

Untreated hyperthyroidism is characterized by increased bone turnover with loss of bone and bone mineral. The aim of the present investigati on was to evaluate the reversibility of these changes by measuring bon e mass, bone turnover, and calcium homeostasis in surgically treated f ormer hyperthyroid patients who had been euthyroid for at least 4 year s. Sixty euthyroid former hyperthyroid patients and 94 normal sex- and age-matched controls participated. Heights and body weights and compo sition were similar in the two groups. In the thyroxine substituted pa tients (n = 27) both serum T-4 and serum free T-4-index (S-FT4I) were increased (p < 0.001) compared to the normal controls as well as the n onsubstituted patients. In the nonsubstituted patients (n = 33), serum TSH was increased (p < 0.001) compared to the normal controls. No sig nificant differences were observed between substituted and nonsubstitu ted patients and normal controls with respect to serum T-3, serum free T-3-index (S-FT3I), or regional or total bone mineral content (BMC) a nd density (BMD) values. Serum levels of calcium, phosphate, magnesium , intact PTH, and renal excretion of calcium were unchanged. However, serum levels of 1,25-dihydroxy- and 25-hydroxyvitamin D were reduced. Urinary excretion of hydroxyproline was increased by 16% (p < 0.05), b ut serum cross-linked carboxy-terminal teleopeptide of type I collagen (ICTP) was decreased by 11% (p < 0.01). Urinary excretion of collagen cross-links was normal. Serum levels of osteocalcin, carboxy-terminal propeptide of human type I procollagen (PICP), and total and bone alk aline phosphatase were all normal. In conclusion, surgically treated f ormer hyperthyroid patients have normal bone mass, bone turnover, and calcium homeostasis in spite of minor variations in thyroid hormones a nd vitamin D metabolites.