SUPPRESSED TSH LEVELS SECONDARY TO THYROXINE REPLACEMENT THERAPY ARE NOT ASSOCIATED WITH OSTEOPOROSIS

OBJECTIVE Recent studies have suggested that patients receiving thyrox ine are at increased risk of osteoporosis. We set out to measure bone mineral densities in two groups of post-menopausal women receiving thy roxine replacement therapy (those with serum TSH levels persistently s uppressed or non-suppressed) and to compare the results in both groups with those of the local control population. DESIGN Cross-sectional st udy. PATIENTS Seventy-eight post-menopausal women who had been treated with thyroxine for primary autoimmune or idiopathic hypothyroidism fo r a minimum of 5 years, 44 with TSH persistently suppressed and 34 non -suppressed. One hundred and two control subjects. MEASUREMENTS Forear m bone mineral density at proximal and distal sites as measured by sin gle-photon absorptiometry. RESULTS Results were expressed as Z-scores, i.e. number of standard deviations from the mean of a 5-year age-band from the local control population. Mean Z-scores at proximal and dist al sites for the non-suppressed patients were - 0.03 and - 0.07 and fo r the suppressed patients were - 0.20 and - 0.25, representing a decre ase in bone mineral density of at most 5% in the suppressed patients. The differences between the three groups were not statistically signif icant. CONCLUSION In this patient population, the reduction in bone mi neral density due to thyroxine is small. It is unlikely to be of clini cal significance and should not on its own be an indication for reduct ion of thyroxine dose in patients who are clinically euthyroid.