Quality of Life, Muscle Strength, and Fatigue Perception in Patients on Suppressive Therapy With Levothyroxine for Differentiated Thyroid Carcinoma

Objectives: The aim of this study was to evaluate the fatigue perception, the muscle function, and the health-related quality of life (QoL) in subclinical hyperthyroidism (SCH) induced by levothyroxine in the treatment of differentiated thyroid carcinoma, in comparison with a group of euthyroid (EU) subjects. Patients and Methods: A cross-sectional study with 38 SCH individuals and 54 EU subjects was performed. They were submitted to Short Form-36 and Chalder questionnaires to evaluate QoL and fatigue, respectively. The tests performed to evaluate muscle function of upper and lower limbs were: maximum quadriceps isometric strength (QS); quadriceps fatigue resistance (T50% QS), QS at 30 seconds (QS30s); quadriceps functional capacity (QFC); maximum isometric handgrip strength (HS); fatigue handgrip resistance (T50% HS), HS at 30 seconds (HS30s); and functional capacity of the shoulder. Results and Conclusions: The SCH patients had worse muscle function, regarding HS (25.19 +/- 7.00 vs. 30.45 +/- 9.98 kgf in EU, P = 0.009) and functional capacity of the shoulder (41.28 +/- 48.36 vs. 56.68 +/- 37.44 s in EU, P = 0.004). The self-perception of fatigue by Chalder questionnaire (23.91 +/- 5.39 vs. 29.77 +/- 7.03, P = 0.000) and the QoL in terms of functional capacity (70.20 +/- 21.57 vs. 56.25 +/- 28.79, P = 0.025), physical aspects (71.42 +/- 36.44 vs. 45.83 +/- 42.88, P = 0.004), pain (62.48 +/- 22.20 vs. 50.05 +/- 24.80, P = 0.035), and emotional aspects (70.74 +/- 38.26 vs. 46.29 +/- 44.56, P = 0.008) were also worse in SCH. In conclusion, the SCH was associated with alterations in the QoL, reduction in the muscle function of upper limbs, and higher degree of fatigue.