High Serum Levels of Thyroid-Stimulating Hormone and Sustained Weight Gain in Patients with Thyroid Cancer Undergoing Radioiodine Therapy

ABSTRACT

BACKGROUND AND OBJECTIVES: The extent of weight gain and its association with clinical factors in patients undergoing radioiodine therapy for differentiated thyroid cancer remain unclear. We analyzed clinical factors related to sustained weight gain after serum thyroid-stimulating hormone (TSH) stimulation for radioiodine (I-131) therapy. MATERIALS AND METHODS: The study population included 301 adult patients who underwent total thyroidectomy followed by radioiodine therapy and visited the thyroid clinic regularly. Group 1 received a single radioiodine therapy treatment, while group 2 received multiple radioiodine treatment. Data on transient weight gain, defined as weight gain that resolved (±5%) within 1 year after radioiodine therapy, were collected from medical records. Sustained weight gain was defined as body mass index after treatment (BMI(post)) - BMI before treatment (BMI(pre)) ≥2 kg/m2 more than 1 year following radioiodine therapy. Subjective symptoms were scored by questionnaire. Logistic regression analysis was performed using various clinical and laboratory factors to identify risk factors associated with sustained weight gain. RESULTS: Two hundred and fifty-nine (86%) patients showed transient weight gain and 23 (8%) patients showed sustained weight gain. TSH at therapy and T4-on TSH differed significantly in all patients and in the patients in group 1 with sustained weight gain. The proportion of patients with basal BMI≥25 kg/m2 in group 1 with sustained weight gain also differed significantly. Univariate analysis revealed that high serum levels of TSH at therapy (≥100 µIU/mL) and hypercholesterolemia were associated with sustained weight gain in group 1. Multivariate analysis showed that TSH at therapy levels ≥100 µIU/mL was associated with sustained weight gain in group 1. Of 283 patients remaining after excluding those with insufficient TSH suppression during follow-up, T4-on TSH levels were lower in the sustained weight gain group compared to those without sustained weight gain. TSH at therapy levels ≥100 µIU/mL were significantly associated with sustained weight gain in multivariate analysis. CONCLUSION: Most patients (86%) had transient weight gain after TSH at therapy, while 8% of patients showed sustained weight gain. Univariate and multivariate analysis revealed relatively high TSH levels (≥100 µIU/mL) to be a risk factor for patients that received a single dose of radioiodine therapy. Insufficient T4 dose was not associated with sustained weight gain.