Effect of thyrotropin suppressive therapy on lumbar bone mineral density in patients with differentiated thyroid cancer: a retrospective cohort study.

Background: To investigate the effect of thyrotropin (TSH) suppressive therapy on lumbar bone mineral density (BMD) in patients with differentiated thyroid cancer (DTC) after operation.

Methods: We retrospectively analyzed 70 DTC patients at intermediate or high risk of recurrence, including 17 males, 30 premenopausal females, and 23 postmenopausal females. All patients were treated with oral 131I to clear any residual thyroid and L-thyroxine tablets to suppress TSH after surgery. The baseline and follow-up lumbar BMD were measured. The anthropometric and biochemical parameters, the doses of calcium supplement, and levothyroxine were collected.

Results: Lumbar BMD in the postmenopausal female group was markedly decreased (regression coefficient: -0.201; P<0.001) compared to the male group and premenopausal female group (both: P>0.05). Further comparisons between groups found that premenopausal women had a monthly lumbar BMD reduction of 0.001 g/cm more than men, but the difference was not statistically significant (P=0.515). In contrast, postmenopausal women had a monthly lumbar BMD reduction of 0.004 g/cm more than men and 0.003 g/cm more than postmenopausal controls (P=0.017 and P<0.001, respectively). Lumbar BMD decreased significantly with the increasing duration of TSH suppression in both the calcium supplement group and the non-calcium supplement group (both: P<0.05), but there was no statistical difference between the two groups (P=0.534).

Conclusions: The longer the duration of TSH suppression in DTC patients after operation, the more significant the decrease of BMD, especially in postmenopausal women. Furthermore, calcium supplementation did not significantly improve lumbar BMD.