Understanding Muscle Pain and Weakness in Thyroid Disease

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Muscle disease, or myopathy, may occur as a result of having an underactive thyroid (hypothyroidism) or an overactive thyroid (hyperthyroidism). As a rule, muscle problems related to these concerns generally are mild and eased with prompt treatment of the thyroid disorder. That said, in less frequent scenarios, myopathy related to thyroid disease can be severe and debilitating.

By gaining a better understanding of the muscle symptoms of thyroid disease, you can hopefully get to the bottom of your discomfort and/or weakness.

Myopathy in Hypothyroidism

  • Weakness in muscles close to the center of the body (thighs, shoulders)

  • Cramping

  • Elevated creatinine

  • Rarely, enlarged muscles (Hoffman's syndrome)

  • Rarely, breakdown of muscle tissue (rhabdomyolysis)

Myopathy in Hyperthyroidism

  • Muscle weakness

  • Issues with the muscles involved in swallowing and breathing (rare)

  • Cramping (uncommon)

  • Creatinine levels tend to be normal

Hypothyroid Myopathy

Muscle weakness, aches, and cramping are common in people with hypothyroidism.

Symptoms

While the weakness can be generalized, people typically experience it in the muscles that are closest to the center of their bodies, such as the thigh or shoulder. This can lead to problems climbing stairs or combing your hair.

In addition to muscle symptoms, you may have an elevated creatinine kinase (CK) level, as determined by a blood test. Creatinine kinase is a muscle enzyme that increases with a muscle injury. The CK level, however, does not necessarily link to the severity of a person's muscle pain.

Rarely, hypothyroidism can cause more severe muscle symptoms. One example is Hoffman's syndrome, in which a person develops diffuse muscle hypertrophy (enlarged muscles) leading to significant muscle stiffness, weakness, and pain.

Rhabdomyolysis (when muscle breaks down rapidly) is another rare muscular manifestation of hypothyroidism. It's often triggered by the combination of being hypothyroid and engaging in vigorous exercise or taking a statin (a cholesterol-lowering medication).

Cause

While the precise cause of hypothyroidism-induced myopathy is still unclear, some experts speculate that the thyroxine (T4) deficiency seen in hypothyroidism leads to abnormal oxidative metabolism, which ultimately causes muscle injury and impaired muscle function.

Diagnosis

Your doctor will ask about your symptoms and do a physical examination. A blood test will be done to measure creatinine kinase. Your doctor may recommend other tests, such as an electromyography (a test that uses electrodes to detect, translate, and record the electrical signals in your muscles and nerve cells while they're active and at rest) or a muscle biopsy, to rule out other conditions, especially if your symptoms are severe.

Treatment

Treatment with the thyroid hormone replacement medication Synthroid (levothyroxine) can usually improve muscle symptoms like cramps and stiffness, although this improvement may take weeks. Muscle weakness generally takes several months to resolve.

Thyroid Replacement Drugs

Hyperthyroid Myopathy

Muscle weakness is the signature symptom in people with hyperthyroidism. While muscle cramps and aches may occur, they are not as common as they are in myopathy related to hypothyroidism. 

Symptoms

Due to muscle weakness, a person may have difficulty climbing stairs, rising from a chair, holding or gripping objects, and reaching their arms above their head. Rarely, in myopathy from hyperthyroidism, the muscles affected can include those that help you swallow and breathe.

The creatinine kinase level in the bloodstream is generally normal despite the fact that there is muscle wasting. Like in hypothyroidism-induced myopathy, the number does not correlate with the severity of a person's muscle symptoms. 

Cause

Like muscle disease in hypothyroidism, the "why" behind myopathy in hyperthyroidism is also unclear. It's likely that the elevated level of thyroid hormones in the body is directly contributing. More specifically, these high thyroid hormone levels may lead to increased muscle protein degradation and muscle energy use.

Diagnosis

As with myopathy in hypothyroidism, your doctor will perform a physical examination and ask you questions related to your muscle symptoms. He may also order blood tests, especially a thyroid function panel, and recommend an electromyography.

Treatment

Treatment of your hyperthyroidism will generally cure the myopathy; however, it can take time—possibly up to several months—even after the thyroid is back to its normal state.

Understanding Your Electromyography Results

A Word From Verywell

Muscle complaints are common in thyroid disease and can generally be alleviated with normalization of your thyroid function. Coping strategies for easing muscle pain, regardless of the cause, may be useful in the meantime: massage, warm baths, gentle exercise, for example.

Still, it's important to see your doctor if you notice new and/or significant muscle pain or weakness. While your thyroid may be the culprit, there are other health conditions that can cause muscle symptoms as well. 

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