Total thyroidectomy: a clue to understanding the metabolic changes induced by subclinical hyperthyroidism?

The effects of endogenous subclinical hyperthyroidism (eSCH) on heart and bone have been well documented. There are only limited data available regarding the impact of eSCH on weight regulation and lipid metabolism. Our aim was to evaluate the changes in body weight and metabolic parameters after total thyroidectomy in patients with pre-operative eSCH compared with pre-operative patients with euthyroid (EUT).

A retrospective study of 505 patients who underwent total thyroidectomy for benign multinodular goitre in an academic hospital in Brussels (Belgium) was performed.

Two hundred and 25 patients were included (eSCH group: n = 74; EUT group: n = 151). The mean follow-up time was 26·1 ± 0·8 months and was similar in both groups.

Absolute BMI gain was significantly greater in the eSCH group than in the EUT group (1·11 ± 0·17 vs 0·33 ± 0·13 kg/m² ; P = 0·003). A significant increase in LDL cholesterol was observed in the eSCH group (16·1 ± 3·8 mg/dl; P < 0·001) but not in the EUT group (0·0 ± 3·0 mg/dl; P = 0·88). In a multivariate model, pre-operative TSH levels were the main factor significantly associated with increases in BMI or LDL cholesterol. Post-operative median TSH levels and L-thyroxine substitution were similar in both groups.

After total thyroidectomy, increases in weight and serum cholesterol were observed in the eSCH group. Given that post-operative TSH levels were similar in the two groups, these observations are probably due to the correction of eSCH, suggesting a direct effect of eSCH on body weight regulation and lipid metabolism.