Thyroid Homeostasis After Bariatric Surgery in Obese Cases.

Background: The aim of this study was to determine changes in thyroid hormones and morphology with weight loss after bariatric surgery in obese patients.
Methods: This prospective study was performed in our endocrinology and surgery clinic. Pre- and post-bariatric surgery thyroid function tests and thyroid ultrasonography parameters were compared.
Results: Four hundred seventy-two patients were included in the study. Mean weight loss after surgery was 30.7 ± 5.1 kg. TSH levels decreased statistically significantly parallel with weight loss and decreased BMI (p = 0.025) after bariatric surgery. However, no statistically significant change was observed in fT4 or fT3 levels (p > 0.05). A significant increase in thyroid parenchyma echogenicity, correlated with weight loss and time elapsed since surgery, was detected at ultrasonography (US) grayscale histogram analysis compared with muscle echogenicity (p = 0.032). An increase in echogenicity was even detected in patients with isoechoic thyroid parenchyma before surgery. Fasting insulin and HOMA-IR levels decreased after surgery (p = 0.010 and p = 0.001, respectively). Patients were divided into three groups based on weight loss. In group 3, preoperative TSH of 4.1 ± 0.7 decreased to 1.6 ± 0.7 postoperatively (p = 0.001), while preoperative HOMA-IR of 4.9 ± 1.9 decreased to 2.4 ± 0.8 postoperatively (p = 0.001).
Conclusions: Obesity causes thyroid hormone resistance through a mechanism similar to insulin resistance and leads to an increase in TSH similar to hyperinsulinemia. Our findings show that echogenicity at thyroid US increases in line with weight loss following bariatric surgery.