Thyrotoxic Myopathy: A Primer for Patients with Hyperthyroidism

Despite the minute size of the thyroid gland, thyroid disorders have been linked to a broad range of symptoms and health problems that span virtually the entire body. The thyroid’s central role in regulating the endocrine system and the production and distribution of hormones throughout the body grant it a unique level of importance and influence that far exceeds its physical size.

Because of the complexity of thyroid-related health problems, researchers are only beginning to understand and document the full extent of some disorders that have their origins in thyroid dysfunction. One example is the neuromuscular disorder thyrotoxic myopathy, which is now recognized as having links to both Grave’s disease and hyperthyroidism. This week, we’ll take a look at the health implications for thyroid patients who are also diagnosed with thyrotoxic myopathy.

What is thyrotoxic myopathy?

Thyrotoxic myopathy is a neuromuscular disorder that is strongly linked to two common thyroid diseases, namely, Grave’s disease and hyperthyroidism. It is sometimes referred to by the alternate names of, Graves myopathy, Basedow’s myopathy, hyperthyroid myopathy, or Basedow paraplegia.

This disease is caused by excessive levels of the thyroid hormone thyroxine, which is a key symptom of both Grave’s disease and hyperthyroidism. Although research into the exact causes of thyrotoxic myopathy remains ongoing, it is believed that excessive production of thyroxine over extended periods of time can result in damage to the muscle fibers.

Some researchers have posited that the excess thyroid hormone can cause an array of problems in muscle components, including acceleration in several key muscle processes, such as lipid oxidation, mitochondrial respiration, and protein degradation. In addition, the presence of too much thyroid hormone can increase the muscle’s beta-adrenergic sensitivity.

Although there is also a type of myopathy that is related to hypothyroidism, it is much less prevalent than the type of thyrotoxic myopathy that is linked to hyperthyroidism and involves a different type of muscular failure.

What are the Symptoms of Thyrotoxic Myopathy?

Literally, the word ‘myopathy’ translates as ‘muscle disease.’ Thyrotoxic myopathy is but one of dozens of different types of muscle diseases. Although each myopathy is associated with a distinct symptom set, most share one major characteristic in common: muscular weakness and loss of muscle function and control. However, the onset of this muscle weakness can be very gradual, so that patients may not report it to their doctor for months or even years after it first becomes noticeable. Another common symptom of the disease is becoming tired and fatigued more easily.

The muscular weakness that is associated with thyrotoxic myopathy is often concentrated in the shoulders, neck area, and hips. In some cases, patients also report a sense of muscle weakness in the face, throat, and eyes. Without proper treatment, functions such as breathing, speaking, and vision can sometimes be adversely affected. The risk of vision problems is particularly high in patients with Grave’s disease.

In patients with chronic cases of thyrotoxic myopathy, the general severity of symptoms is often minimal to moderate. However, in rarer cases of acute thyrotoxic myopathy, the distress level can be intense. Over time, improperly treated cases of thyrotoxic myopathy can result in disintegration of the muscle tissue, a condition known as rhabdomyolysis. Some patients also experience bouts of temporary paralysis as a result of the disease.

Diagnosis, Treatment, and Prognosis of Thyrotoxic Myopathy

In some cases, achieving an accurate diagnosis of the disease can be challenging. This is particularly true in mild or moderate cases in which the onset of symptoms is very gradual. However, if patients have already been diagnosed with hyperthyroidism or Grave’s disease, physicians are usually aware of the risk that muscle-related symptoms can pose. Still, it is vitally important to report any increases in fatigue or weakness as soon as they are noticeable.

Like many disorders that have their origins in thyroid dysfunction, most of the symptoms of thyrotoxic myopathy can often be reversed if patients adhere closely to their prescribed regimens of thyroid medication. Because an excess of thyroid hormone causes this disorder, taking medication to balance thyroid hormone levels can often, in effect, “cure” the symptoms of thyrotoxic myopathy.

In most cases, problems with muscular weakness and general fatigue can be eliminated in less than six months after thyroid levels have been balanced through medication. However, it may take as long as a year of treatment for muscles to regain any lost tissue or muscle mass.

Compared to many other thyroid-related disorders, the prognosis for thyrotoxic myopathy is quite good. If patients remain consistent in their adherence to prescribed medications, it is likely that they will soon be able to regain their full health and well-being.

For Further Reading

• http://www.mdausa.org/publications/fa-myop-qa2.html

• http://www.emedicine.com/neuro/byname/endocrine-myopathies.htm