Thyrotoxic myopathy is a neuromuscular disorder that may accompany hyperthyroidism (Graves' disease, caused by overproduction of the thyroid hormone thyroxine). Symptoms may include muscle weakness, wasting of the pelvic girdle and shoulder muscles, fatigue, and heat intolerance. Muscle breakdown may occur in acute cases. Physical acts such as climbing stairs may be difficult. Patients may develop muscle damage to the eyes and eyelids, which may affect mobility of the eye muscles, and temporary, but severe, attacks of muscle weakness known as periodic paralysis.

Treatment is based on treatment for hyperthyroidism and may include prescription of iodine and other drugs, beta-blockers, and surgery. Myopathy may improve by restoring normal thyroid function. Complete or partial removal of the thyroid may be required in severe cases.

With treatment, muscle weakness may improve or be reversed.

Prepared by the National Institutes of Health