Effects of Physical Activity on Body Composition and Fatigue Perception in Patients on Thyrotropin-Suppressive Therapy for Differentiated Thyroid Carcinoma (Original STUDIES, REVIEWS, AND SCHOLARLY DIALOG: THYROID FUNCTION AND Dysfunction) (Report‪)‬

Introduction DIFFERENTIATED THYROID CARCINOMA (DTC) accounts for 90% of all thyroid malignancies (1). In the last decades, there has been an increase in the incidence of DTC, possibly as a result of improved diagnostic methods and their more widespread use. Thyroid nodules are very common, though only about 5%-10% of them are malignant. The conventional treatment for DTC consists of total or partial thyroidectomy, often followed by ablation of the thyroid remnants with [sup.131]-I. Following these procedures, patients require levothyroxine (LT4) treatment (2), and currently most are given doses that suppress serum thyrotropin (TSH). Therefore, [LT.sub.4] treatment in patients with a history of DTC is a common cause of so-called subclinical hyperthyroidism (subclinical thyrotoxicosis [scTox]), which is characterized by serum TSH concentrations that are low with normal serum free T4 ([FT.sub.4]) and free triiodothyronine concentrations (3). Epidemiological data indicate a wide variation in the prevalence of scTox, from less than 1% to about 16%. Among other things, it is influenced by gender, the underlying disease, age, the assignment for what the lower limit of the normal range for TSH is, and the methods used to measure serum TSH concentrations (4-6). Cardiovascular, neuromuscular, and psychological alterations have been described in scTox, and many clinical parameters have been evaluated (7).