Endocrine Abstracts

Introduction: Patients who do not develop overt hypothyroidism after hemithyroidectomy for benign euthyroid goiter have permanently increased serum levels of TSH and decreased levels of thyroid hormones within the reference ranges. Thyroid hormones are major regulators of mitochondrial function, and the mitochondrial membrane potential (MMP) can be measured by flow cytometry analysis of living cells as the fluorescence intensity of stained peripheral mononuclear blood cells (MNBCs). We have previously shown increased MMP of MNBCs in patients with subclinical hypothyroidism. Increased MMP might represent increased production of reactive oxygen species rather than of ATP.

Aim: To determine if the hemithyroidectomy-induced change in TSH and thyroid hormones affects the mitochondria of peripheral MNBCs.

Method: In an ongoing prospective study, patients are examined at one time point before and at four time points (1, 3, 6, and 12 months) after hemithyroidectomy for benign euthyroid goiter. TSH, fT4 and tT3 are measured and the MMP is measured as the fluorescence intensity of MitoTracker Green (MTG)- and Tetramethylrhodamine methyl ester (TMRM)-stained MNBCs by flow cytometry analysis.

Results: We present a 6-month follow-up of 22 hemithyroidectomized patients who do not receive levothyroxine treatment. TSH shows a persistent increase (median 0.97 mUl/l versus median 2.95 mUl/l, P<0.000), and fT4 (median 16.0 pmol/l vs median 15.20 pmol/l, P<0.003) and tT3 a persistent decrease (median 1.89 nmol/l vs median 1.73 nmol/l, P<0.004) within the reference ranges, unchanged to values 1 month after hemithyroidectomy. The MMP of MNBCs was persistently increased after six months (median 4079 TMRM fluorescence a.u. vs median 6327 a.u., P=0.002).

Conclusion: Although they are considered clinically and biochemically euthyroid, hemithyroidectomized patients have lowered thyroid function and hyperpolarized mitochondria. It is unknown if these effects of hemithyroidectomy have clinical consequences.