TSH oscillations in young patients with type 1 diabetes may be due to glycemic variability

A relationship between thyroid dysfunction and diabetes mellitus has been described by several authors but the role of glycemic variability is still unclear. We planned the present study to evaluate the influence of glycemic variability on thyroid hormones and TSH concentrations in patients with type 1 diabetes mellitus (T1DM). Seventy-seven young patients with T1DM were enrolled and evaluated for basal glucose concentrations, HbA1c, thyroid hormones and TSH concentrations. Glucose variability was investigated by considering the standard deviation of blood glucose readings and by calculating the mean amplitude of glycemic excursions and continuous overlapping net glycemic action (CONGA). The low (LBGI) and high (HBGI) blood glucose indices were also calculated. The correlations between TSH, thyroid hormones, glycemia and HbA1c were studied in patients and in controls, whereas those between TSH, thyroid hormones and indices of glucose variability only in patients. No correlations were observed in T1DM patients between free thyroid hormones and glycemic values, HbA1c and indices of glucose variability, while an inverse correlation was observed between TSH levels and glycemic values (r= −0.27; p= 0.01), CONGA index (r= −0.35; p= 0.001) and HBGI (r= −0.28; p= 0.01) but not with HbA1c (r= −0.1; p= 0.47). Our results suggest a direct action of glycemic excursions on TSH secretion, regardless of variations of thyroid hormone concentrations. Thus, the evaluation of thyroid function through the assay of TSH concentrations in these patients should be made, if possible, by multiple samples on patients in euglycemic state to avoid underestimation or overestimation of thyroid dysfunction due to a wrong diagnosis of euthyroidism or dysthyroidism with consequent inappropriate choice of therapeutic options.