Objective: The present study aimed to evaluate the performance of knee muscles using an isokinetic dynamometer to determine muscle dysfunction in patients with newly diagnosed hypothyroidism, and to compare the results with that in a healthy control group.

Materials and Methods: Thirty patients diagnosed with subclinical hypothyroidism and 20 patients diagnosed with overt hypothyroidism, and 30 healthy volunteers were included in the study. A visual analogue scale (VAS) was used to determine the severity of fatigue. Using an isokinetic dynamometer, the peak torque values during knee flexion and extension were measured at angular velocities of 60°/s and 180°/s, and the total work were measured at the angular velocities of 180°/s.

Results: The mean VAS score in patients with overt hypothyroidism was significantly higher than that in those with subclinical hypothyroidism. The isokinetic peak torque values at the angular velocities of 60°/s and 180°/s for the quadriceps muscle and for the hamstring muscle was statistically significantly different in the overt and subclinical hypothyroidism groups than in the control group. The isokinetic total work at 180°/s was significantly different in the overt and subclinical hypothyroidism groups than in the control group. Although total work were higher in the subclinical hypothyroidism group than in the overt hypothyroidism group, the differences were not statistically significant.

Conclusion: The lower muscle strength and endurance determined in overt and subclinical hypothyroid patients as compared to the controls suggest that myopathy occurs in the early stages of hypothyroidism and that it is a condition that should be evaluated at the time of diagnosis.