ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2019) 64 016 | DOI: 10.1530/endoabs.64.016

Is it worthwhile to distinguish between grade 1 and grade 2 subclinical hyperthyroidism for alteration of metabolic parameters?

T Nguyen, L Russo, A Kyrilli, R Moreno-Reyes & B Corvilain

Hôpital Erasme – Cliniques Universitaires de Bruxelles, Bruxelles, Belgium.

Aim of the work: The effects of subclinical hyperthyroidism (SCH) on bone and heart have been well documented. Effects on other parameters like lipids metabolism and weight regulation have also been reported but mainly in cross-sectional studies. The potential benefits of treatment of endogenous subclinical hyperthyroidism are more controversial as few large controlled studies on clinical outcomes have been performed. ATA guidelines recommend treatment according to the severity of the disease (grade 1 SCH (TSH between 0.10 and 0.39 mU/l) or grade 2 SCH (TSH < 0.10 mU/l) and clinical parameters (age, menopausal status, cardiovascular disease, osteoporosis…). The aim of our work was to evaluate changes in body weight and lipids parameters following radioiodine treatment in patients with SCH caused by benign nodular goiter and to compare the results obtained in grade 1 and grade 2 SCH.

Methods: All of the 146 files of patients with nodular goiter treated by radioiodine for SCH between January 2008 and July 2018 and who had a follow-up in Erasme Hospital were retrospectively reviewed and separated into two groups according to their pre-treatment thyroid status: one group with pre-treatment grade 1 SCH and one group with pre-treatment grade 2 SCH. 58 patients were excluded from the study. The causes of exclusion were: cancer including thyroid cancer (n=24), death during follow up (n=2), any condition likely to affect weight changes during follow-up such as corticoids treatment (n=16), or other causes (n=16). TSH levels, evolution in weight and serum lipids values were recorded up to 3 years after radioiodine treatment. Patients were included in the study if at least one body weight was reported in their file during the 1–3 years follow-up. Results are expressed as means ± S.E.M.

Main results: Out of the 88 eligible patients, 74 had at least one body weight reported in their file during the 1–3 years follow-up period and were included in this study. After radioiodine therapy, euthyroidism was achieved in 91.8% patients after 1 year. Pre-treatment median TSH was 0.19 mU/l in grade 1 SCH group and 0.04 mU/l in the grade 2 SCH group (P<0.01). Mean follow-up time was 2.47 years and did not significantly differ between the groups (P=0.352). Before radioactive iodine treatment, BMI of patients with grade 1 and grade 2 SCH were 27.5±0.9 kg/m2 and 26.9±0.9 kg/m2 respectively (P=0.664). Post-treatment median TSH levels was similar in both groups. Post radioactive iodine treatment weight gain was significantly higher in the grade 2 group (2.20±0.73 kg) than in the grade 1 group (0.65±0.39 kg); P=0.039. Increase in BMI was also higher in grade 2 group (1.07±0.27 kg/m2) than in the grade 1 group (0.26±0.15 kg/m2); P=0.023. Most of the weight gain was already observed within the first 12 months of follow-up. After radioactive iodine, a significant increase in LDL cholesterol values of 14.3±4.1 mg/dl (n=19, P=0.003) was observed in grade 2 group and not in grade 1 group (10.2±6.9 mg/dl, n=19, P=0.157). A negative correlation was observed between pre-treatment TSH levels and absolute BMI gain (r=−0.350; P=0.005). Our study found no significant modifications in glucose after restoration of euthyroidism.

Conclusions: In the follow-up of patients receiving radioiodine therapy for SCH caused by benign nodular goiter, weight gain and raise in serum cholesterol were observed only in the group with SCH grade 2 and not in the group with SCH grade 1. As post treatment TSH values were similar in both groups, this observation is probably related to the severity of the disease before treatment confirming that the distinction between grade 1 and grade 2 SCH is clinically relevant at least for metabolic parameters.

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