Understanding Muscle Pain and Weakness in Thyroid Disease

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Muscle disease, called myopathy, may occur as a result of having an underactive thyroid (called hypothyroidism) or an overactive thyroid (called hyperthyroidism).

The good news is that the symptoms of thyroid-related myopathies, such as muscle pain, weakness, or stiffness, are generally mild and eased with prompt treatment of the thyroid disorder. That said, in less frequent scenarios, a person's myopathy related to their thyroid disease can be severe and debilitating.

By gaining a better understanding of the muscle symptoms of thyroid disease (and how they would be accessed and treated by your doctor), you can hopefully get to the bottom of your discomfort and/or weakness.

Mypopathy can be seen in both hypothyroidism and hyperthyroidism but can usually be alleviated by treating the underlying thyroid disorder.

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 comb your hair.

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

Rarely, more severe muscle manifestations from hypothyroidism may develop. 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 with 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

The diagnosis of hypothyroidism-induced myopathy is clinical, meaning your doctor will diagnose it based on your symptoms and physical examination. A blood test will be done to measure creatinine kinase. Your doctor may recommend other tests, like an electromyography or a muscle biopsy, to rule out other conditions, especially if your symptoms are severe.

Treatment

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

Hyperthyroid Myopathy

Muscle weakness may develop in people with hyperthyroidism.

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 breath.

Interestingly, while muscle cramps and aches may occur, they are not as common as they are in a myopathy related to hypothyroidism. 

The creatinine kinase level in the bloodstream is generally normal, despite the fact, 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 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, up to several months potentially, even after the thyroid is back to its normal state.

A Word From Verywell

The take-home message here is that muscle complaints are common in thyroid disease and can generally be alleviated with normalization of your thyroid function.

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, and these conditions require a different treatment plan. 

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