Muscle Performance and Postural Stability Are Reduced in Patients with Newly Diagnosed Graves' Disease

Background: Reduced muscle strength is an acknowledged symptom of Graves' disease, but the knowledge on severity is sparse. This study aimed to investigate muscle strength, balance, and muscle function in patients with Graves' disease compared to age-and sex-matched healthy controls. Methods: Using a cross-sectional design, 55 patients newly diagnosed with Graves' disease were compared to 55 euthyroid controls, matched on sex, age, and menopausal status. Isometric muscle strength (N) and maximum force production (N/s) were measured across different muscles groups using a dynamometer chair and postural stability (balance) in different positions using a stadiometer. Muscle function was assessed using the Timed-Up-and-Go test and the Repeated Chair Stand test. Results: Patients and controls were well matched. Handgrip maximum muscle strength as well as strength at elbow and knee flexion and extension were significantly impaired in patients compared to controls. Maximum force production was only significantly reduced at elbow flexion. Patients performed the Timed-Up-and-Go and the Repeated Chair Stand test significantly slower than controls, and postural stability was significantly reduced in patients compared to controls in all positions. Free triiodothyronine correlated with reduced muscle strength and postural stability. Conclusions: At the time of diagnosis, Graves' disease is associated with impaired maximum muscle strength, performance, and balance, whereas maximum force production is overall comparable to euthyroid controls.