Thyrotoxic Myopathy

Thyrotoxic myopathy (TM) is a neuromuscular disorder that may accompany hyperthyroidism (Graves’ disease, caused by overproduction of the thyroid hormone thyroxine).

While hyperthyroidism is more common in women, the development of TM is more common among men with hyperthyroidism.

Symptoms may include:

  • Muscle weakness
  • Wasting of the pelvic girdle
  • Wasting of the shoulder muscles
  • Fatigue
  • 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.

Patients who are diagnosed with TM have a normal life expectancy and can ultimately lead healthy lives if proper treatment is administered. The effects of TM can be controlled and in most cases reversed, leaving no lasting effects. However, untreated TM can eventually cause severe respiratory distress or even arrest, possibly leading to death, yet this is very rarely seen.

Treatment is based on treatment for hyperthyroidism and may include:

  • Prescription of iodine and other drugs
  • Beta-blockers
  • Surgery

Myopathy may improve by restoring normal thyroid function. Complete or partial removal of the thyroid may be required in severe cases.

Typically, once the over production of thyroxine is corrected and thyroid function adequately reaches a stable level, patients begin to regain muscle strength within two to four months. Depending on the severity of the TM symptoms, it may take up to a year to completely reverse the damage done.