Although I can’t say that most of my patients experience muscle weakness, I also can’t say that it’s uncommon. While I see it more in my patients with hyperthyroidism and Graves’ disease, people with hypothyroidism and Hashimoto’s can also experience muscle weakness. In this post I’ll discuss the relationship between muscle weakness and thyroid health, along with other factors that can cause this.
Just as a refresher, there are two main types of thyroid hormones. Thyroxine (T4) is the hormone most abundantly produced by the thyroid, while triiodothyronine (T3) is the active form of thyroid hormone. Both of these can influence muscle physiology, although T3 is probably the most studied of the two (1) .
Do You Really Have Muscle Weakness?
There are a few different ways of measuring muscle weakness to make sure it’s not just overall fatigue the person is experiencing. One tool is the Medical Research Council Manual Muscle Testing scale. The differential diagnosis of true muscle weakness is extensive, including neurologic, rheumatologic, endocrine, genetic, medication- or toxin-related, and infectious etiologies (2) . Electromyography is also considered in some cases, as it can confirm the presence of a myopathy, and if a muscle biopsy is necessary it can identify an appropriate biopsy site (3) . Speaking of doing a muscle biopsy, this is usually reserved for people who present with acute or progressive muscle weakness who are suspected of having an underlying neuromuscular disorder (4) .
Sarcopenia and Thyroid Health
The age-related loss of muscle mass, strength, and quality is known as sarcopenia. There is evidence that thyroid hormone can play a role in sarcopenia in a few different ways. First of all, it can cause the transition from a slower fiber type into a faster one, which can play a role in sarcopenia (5) . Skeletal muscle quality also relies on the health of the mitochondria (6) , and skeletal muscle mitochondrial function is also modulated by T3 (7) .
Hyperthyroidism and Muscle Weakness
It is quite common for my hyperthyroid patients to experience a loss of muscle mass. In fact, this was also the case with me when I dealt with Graves’ disease back in 2008/2009. Keep in mind that the loss of muscle mass isn’t synonymous with “muscle weakness”, but some people do experience both problems. The good news is that once the hyperthyroidism has been corrected, over time the person’s muscle mass should increase and the muscle weakness should subside…unless of course if there is another factor responsible for the reduced muscle mass/muscle weakness.
While many people with hyperthyroidism notice that they have a decrease in muscle mass, one of the markers that correlates with this is serum creatinine. This is part of a comprehensive metabolic panel, and when someone with hyperthyroidism has decreased muscle mass the serum creatinine is usually low. Normalizing the thyroid hormone levels may help to normalize the creatinine, but this isn’t always the case, as you might also need to do other things to increase the muscle mass, such as eat enough protein and do weight-bearing exercises.
It’s also worth mentioning that some rare muscle myopathies are associated with hyperthyroidism, including myasthenia gravis. And studies show that treating the hyperthyroidism can improve the muscle response in myasthenia gravis patients (8) .
Speaking of studies, I did come across a study which looked to demonstrate the degree of muscle weakness in newly diagnosed patients with Graves’ disease, as well as assess the response to treatment (9) . This was a small study, involving 10 patients, and results showed that muscle weakness is commonly associated with hyperthyroidism and can be profound. It also showed that the beta blocker  Propranolol can improve muscle weakness in people with hyperthyroidism. Even though Propranolol can decrease the conversion of T4 to T3 I’m still surprised they didn’t use antithyroid medication  in the study, although they might have chose to have the patients take Propranolol because side effects are more common with antithyroid meds such as methimazole.
Hypothyroidism and Muscle Weakness
While an excess of thyroid hormone can be a factor in muscle weakness, low thyroid hormones can also be a factor. Thyroid hormone plays an important role in muscle physiology, and while some people who have subclinical hypothyroidism might not experience muscle weakness, it is actually very common for those with overt hypothyroidism. In other words, if the thyroid hormones are outside of the lab reference range then there is a pretty good chance that muscle weakness will eventually develop.
In fact, a study I came across showed that hypothyroid myopathy affects almost 80 percent of people with hypothyroidism (10) . Hypothyroid myopathy is a condition that presents with nonspecific symptoms of muscle pain, muscle cramps, fatigue, and muscle weakness, particularly exacerbated with exertion and exercise (10) . The authors mentioned that the degree of muscle weakness doesn’t always correlate with the severity of thyroid hormone deficiency.
As for the underlying mechanisms causing the muscle weakness, according to the same study, “T4 deficiency leads to a reduced mitochondrial oxidative capacity, abnormal glycogenolysis (the breakdown of glycogen into glucose) and an insulin resistant state of the cell. This leads to selective atrophy of type 2 muscle fibers (fast-twitching type) as they are dependent on glycolysis for energy causing the slowing of muscle contraction seen clinically in patients with hypothyroidism. Muscle hypertrophy ensues as a result of this, which is believed to be a compensatory response that happens from the accumulation of glycosaminoglycans in the muscle. Increase in connective tissue and muscle fibers also contributed to this hypertrophy”.
If you experience muscle weakness associated with hypothyroidism, there might also be an increase in the marker creatine kinase in the blood. However, there can be other factors that can increase this marker. The good news is increasing the thyroid hormone levels (i.e. with thyroid hormone replacement) can resolve many cases of muscle weakness, although it can take a number of months for this to occur, and sometimes even several years.
Other Causes of Muscle Weakness
As I’m sure you can imagine, there can be many other causes of muscle weakness. Here are some other potential causes:
- Amyotrophic lateral sclerosis
- Cerebral lesion (stroke, hemorrhage, mass)
- Compressive neuropathy of the peripheral nerve
- Guillain-Barré syndrome
- Motor neuropathy
- Multiple sclerosis
- Adrenal insufficiency (Addison disease)
- Endogenous glucocorticoid excess (Cushing syndrome)
- Certain medications
- Certain toxins
- Electrolyte disturbances
- Genetic (i.e. muscular dystrophy)
I’m not going to cover all of these causes, but I do want to briefly discuss a few of them, including electrolyte disturbances, medications, and infections. Regarding electrolyte imbalances, while a comprehensive metabolic panel isn’t a perfect way of evaluating the electrolytes, if someone does have low sodium, potassium, and/or calcium then it’s something to pay attention to. RBC magnesium can help determine if someone has a potassium deficiency.
Some of the medications that can potentially lead to muscle weakness include statins (11) , glucocorticoids (12) , and fluoroquinolones (13) . It’s worth mentioning that the research shows that for those experiencing muscle weakness caused by taking statins, supplementing with CoQ10 can potentially help with this (14) . CoQ10 might also benefit some people with hyperthyroidism in general, and not just those experiencing muscle weakness.
Certain infections can also result in muscle weakness. This includes West Nile virus infection, HIV infection, Lyme disease, diphtheria, dengue fever, neurocysticercosis, trichinosis, Chagas disease, rabies, botulism, herpes zoster, cytomegalovirus infection, hepatitis C, and herpes simplex virus 1 infection (15) . When I was diagnosed with chronic Lyme disease  in 2018 I experienced some muscle weakness initially, although thankfully it resolved pretty quickly.
How To Overcome Muscle Weakness
As for what you can do to overcome muscle weakness, you of course need to address the cause of the problem. If someone has muscle weakness due to hyperthyroidism or hypothyroidism then of course these thyroid hormone imbalances need to be corrected. If someone has reduced muscle mass and muscle weakness then not only does the underlying cause need to be addressed, but some weight bearing exercises may also be necessary. As I mentioned earlier, I commonly see this with my hyperthyroid patients, as many of them suffer from reduced muscle mass, and while correcting the hyperthyroidism is important, doing this alone isn’t always sufficient.
I mentioned other potential causes of muscle weakness, and so if any of these are factors then these would also need to be addressed. For example, if someone has overt hypothyroidism and also has chronic Lyme disease, and if both are factors in the muscle weakness, then it shouldn’t be surprising that both the hypothyroidism and chronic Lyme disease condition would need to be addressed.
Do You Experience Muscle Weakness?
If you currently experience muscle weakness, or if you experienced it in the past and have overcome it, please feel free to share your experience in the comments below. Thank you!