Measurement of bone collagen degradation in hyperthyroidism and during thyroxine replacement therapy using pyridinium cross-links as specific urinary markers.

UNLABELLED: Urinary excretion of the bone collagen derived pyridinium cross-links pyridinoline (PYD) and deoxypyridinoline (DPD) was measured in 19 patients (4 M:15 F) with untreated thyrotoxicosis, and 20 pre-, and 20 postmenopausal women taking T4 100-200 micrograms daily for autoimmune hypothyroidism. Both PYD and DPD excretion (nanomoles per mmol creatinine) was elevated in the thyrotoxic patients compared to 287 controls; median 131 vs. 26 and 37.5 vs. 7.2, respectively, P less than 0.0001. In premenopausal women mean urinary pyridinium cross-link excretion and serum osteocalcin levels were similar in both T4-treated and matched control groups, despite suppression of serum TSH concentrations to below 0.1 mU/L in 14 of the 20 taking T4. In postmenopausal women mean (+/- 1 SE) urinary PYD excretion (nanomoles per mmol creatinine) was raised in those taking T4, relative to euthyroid controls; 40.0 +/- 2.7 vs. 32.1 +/- 2.3, P less than 0.05. DPD excretion and serum osteocalcin levels were also higher, but not significantly. When only the T4-treated women with a subnormal serum TSH were considered the difference in PYD excretion was more marked, and mean DPD excretion was also significantly elevated; 13.7 +/- 1.3 vs. 10.1 +/- 0.8, P less than 0.05.

CONCLUSION

bone collagen breakdown is increased in thyrotoxicosis, and in postmenopausal women taking sufficient T4 to suppress serum TSH. Similarly treated premenopausal women appear to be at lower risk.