Iatrogenic hyperthyroidism does not promote weight loss or prevent ageing-related increases in body mass in thyroid cancer survivors.

Context: Thyroid cancer survivors represent a unique population in which the potential long-term effects of brief periods of intentional thyroid hormone withdrawal and/or prolonged periods of iatrogenic hyperthyroidism on body weight and body mass were evaluated.

Objectives: The objectives of this study were to characterize body mass changes over several years in a cohort of thyroid cancer patients with iatrogenic hyperthyroidism and to compare these changes with the expected weight gain in age-matched healthy control populations. We also evaluated the possibility that the method of preparation [thyroid hormone withdrawal (THW) vs recombinant human TSH (rhTSH)] for radioactive iodine remnant ablation may be associated with differences in body mass at the time of the final follow-up. DESIGN/SETTING/PATIENTS/INTERVENTIONS: A retrospective review identified 153 patients with thyroid cancer who underwent total thyroidectomy at one major medical centre. Of the 153 patients, 143 also had radioactive iodine remnant ablation: 70 after THW and 73 after rhTSH.

Main Outcome Measures: Change in weight and BMI at 1-2 and 3-5 years of follow-up points were examined. Annualized weight variation within the cohort was compared with age-matched population controls expressed in kilogram/year.

Results: Significant weight gain was noted for the full cohort after 3-5 years of follow-up as compared to baseline (76 ± 21 kg at baseline vs 79 ± 23 kg at 3-5 years of follow-up, P < 0·01), which represented a 3·2% increase. Female and male patients with thyroid cancer experienced 0·46 and 0·94 kg/year gain in weight, respectively, which is similar or somewhat higher than previously published age-matched population controls (ranging from 0·23 to 0·34 kg/year). When expressed as per cent change and comparing the final weight to the pre-operative baseline, the rhTSH group experienced approximately a 1·7% increase in weight compared with the 3·9% increase seen with THW patients (P = 0·02). When expressed as kg/year change, the rhTSH cohort had 0·34 kg/year change compared with the 0·64 kg/year change seen in the thyroid hormone withdrawal patients (P = 0·02).

Conclusion: In otherwise, healthy patients with differentiated thyroid cancer, significant weight gain occurred during the 3-5 years of follow-up despite ongoing thyrotropin suppression. The data suggest that mild iatrogenic hyperthyroidism does not promote weight loss or prevent ageing-related weight gain. Greater weight gain was seen in patients prepared for radioactive remnant ablation with THW than with rhTSH.