If you have myasthenia gravis, your risk of thyroid disease is higher than that of the general population. It’s estimated that between 5 percent and 10 percent of people with myasthenia gravis also have thyroid issues. The good news is that thyroid disease is very treatable when diagnosed and treated early.

What Does Your Thyroid Do?

Your thyroid is a butterfly-shaped gland located below your Adam’s apple, at the front of your neck. The thyroid gland is part of your endocrine system — the organs responsible for making and releasing hormones. The hormones your thyroid releases are called thyroid hormones.

Everything your body does, from exercising and accomplishing daily tasks to simply staying alive, requires energy. Thyroid hormones control metabolism — the process your body uses to turn food into energy. The two thyroid hormones, thyroxine (also known as T4) and triiodothyronine (T3), tell your body how much energy to use.

Thyroid hormones control metabolism — the process your body uses to turn food into energy — and how much energy your body uses.

Your pituitary gland helps control the levels of thyroid hormones in your blood. If your levels are too low, your pituitary gland will release thyroid-stimulating hormone (TSH). TSH tells your thyroid gland to make more thyroid hormone.

When your thyroid is working well, your metabolism will make and burn energy at the right rate. If this gland isn’t working properly, your body may produce either too much thyroid hormone (hyperthyroidism) or not enough (hypothyroidism).

How Is Thyroid Disease Related to Myasthenia Gravis?

Thyroid issues are relatively common. According to one estimate, thyroid disease affects 5 percent of people in the United States. On the other hand, myasthenia gravis is rare. In the U.S., about 37 in 100,000 people have the condition. Compared with the general population, people with myasthenia gravis are more than twice as likely to develop thyroid diseases. The risk also increases over time.

It’s thought that thyroid disease may be related to myasthenia gravis because both conditions stem from immune system dysfunction. Researchers have found that people with myasthenia gravis and autoimmune thyroid disorders may have some genes in common. Viral infections and certain medications may also trigger myasthenia gravis or thyroid problems.

Myasthenia gravis and some types of thyroid disease are autoimmune disorders. Autoimmune disorders happen when your body makes autoantibodies — immune system proteins that mistakenly attack healthy tissue.

Myasthenia gravis is caused by antibodies attacking acetylcholine receptors (AChRs). These receptors are found in the neuromuscular junction — the space where nerves and muscles meet. When antibodies attack and destroy AChRs, your nerves have trouble communicating with your muscles.

Some thyroid diseases are caused by antibodies attacking the thyroid. This situation can lead to either hyperthyroidism or hypothyroidism.

1. Graves’ Disease

The most common type of thyroid disease that occurs with myasthenia gravis is Graves’ disease, a type of autoimmune thyroid disease that causes hyperthyroidism. People with Graves’ disease make an antibody called thyroid-stimulating immunoglobulin (TSI). TSI binds to the TSH receptor and tells your thyroid to produce more hormone.

Too much thyroid hormone (also called thyrotoxicosis) can cause several body functions to speed up. Possible symptoms of Graves’ disease include:

• Rapid heart rate
• Heart palpitations (irregular heartbeat)
• Nervousness
• Anxiety
• Weight loss
• Excessive sweating
• Insomnia (trouble falling asleep or staying asleep)
• Hair loss or brittle hair
• Changes to the menstrual cycle
• Diarrhea
• Enlarged thyroid gland

Graves’ disease can also cause symptoms that resemble those of myasthenia gravis, especially when it affects the muscles around the eyes. For example, both conditions can cause muscle weakness and changes in eye appearance and function. In Graves’ disease, the eyes may appear to bulge. Other symptoms of Graves’ eye disease (also called thyroid eye disease) can be similar to those of ocular myasthenia gravis and include:

• Diplopia (double vision)
• Blurred vision
• Dry eyes
• Swollen or puffy eyelids
• Sensitivity to light
• Pressure or pain in the eyes

There’s a high prevalence of Graves’ disease in people with ocular myasthenia gravis and in those with mild generalized myasthenia gravis.

Graves’ Disease Treatment

Graves’ disease can be managed with treatments that aim to balance thyroid function. Your treatment plan may include antithyroid medications, radioiodine therapy, or thyroidectomy (surgery to remove the thyroid gland). It’s possible that treating hyperthyroidism due to Graves’ disease may worsen some myasthenia gravis symptoms. However, treating Graves’ disease usually improves eye- and vision-related symptoms in people with both conditions.

If you have both Graves' disease and myasthenia gravis, treating your thyroid condition may improve eye- and vision-related symptoms in both conditions.

2. Hashimoto’s Thyroiditis

Hashimoto’s thyroiditis (also called Hashimoto’s disease) is another type of autoimmune thyroid disease that can occur in people with myasthenia gravis. People with Hashimoto’s thyroiditis have hypothyroidism. Low thyroid hormone levels are caused by antibodies that attack healthy thyroid tissue (also known as antithyroid antibodies). This results in inflammation that damages the gland and may interfere with thyroid function and hormone production.

Common symptoms of Hashimoto’s thyroiditis include:

• Fatigue (persistent exhaustion that doesn’t improve with rest)
• Weight gain
• Difficulty tolerating cold temperatures
• Slow heart rate
• Hair loss or brittle hair and nails
• Dry skin
• Depression
• Constipation
• Heavy or irregular menstrual periods
• Fertility problems
• Pain in joints and muscles
• Concentration difficulties

In people with myasthenia gravis, Hashimoto’s thyroiditis is less common than Graves’ disease. However, Hashimoto’s disease has been linked to more severe myasthenia gravis. In a 2019 study, researchers observed people with myasthenia gravis and thyroid disorders over 20 years. They found that people with Hashimoto’s thyroiditis needed more aggressive treatment for myasthenia gravis. In addition, myasthenia gravis was more often linked to thymoma (tumor in the thymus gland).

People with Hashimoto’s disease and myasthenia gravis tend to have more severe myasthenia gravis symptoms that call for more aggressive treatment.

Hashimoto’s Thyroiditis Treatment

Hashimoto’s thyroiditis is most commonly treated with a synthetic (laboratory-made) version of T4 thyroid hormone called levothyroxine.

3. Thyroid Antibodies With Normal Thyroid Hormone Levels

If you have antithyroid or TSI antibodies, you may still have normal thyroid hormone levels — known as being euthyroid — and not experience any symptoms. In a 2017 study, researchers linked myasthenia gravis to all types of thyroid issues, even in the case of normal thyroid hormone levels.

Treatment for Thyroid Antibodies

You may not need treatment for thyroid antibodies if you have normal thyroid hormone levels. Instead, your doctor may follow up with you to make sure your thyroid hormone levels stay balanced.

4. Thyroid Cancer

Cancer that starts in the thyroid is also associated with myasthenia gravis in rare instances. Clinical features of thyroid cancer include:

• A lump in the neck
• Difficulty swallowing
• Difficulty breathing
• Hoarse voice
• Swollen lymph nodes in the neck

Thyroid Cancer Treatment

Treatment options for thyroid cancer may include:

• Surgery to remove all or part of the thyroid gland
• Radioiodine therapy
• Radiation therapy
• Chemotherapy
• Hormone therapy

5. Goiter

A goiter is a lump in the neck caused by an enlarged thyroid gland. Graves’ disease, Hashimoto’s thyroiditis, and thyroid cancer can all lead to goiter. Iodine deficiency, pregnancy, and thyroid inflammation may also result in goiter.

Goiters are classified as toxic or nontoxic. A toxic goiter creates too much thyroid hormone, whereas a nontoxic goiter doesn’t affect thyroid hormone levels. More severe types of myasthenia gravis may have a higher risk of toxic goiters.

Goiter Treatment

Treatment for goiter is directed at its underlying cause, such as Graves’ disease or Hashimoto’s thyroiditis.

Talk to Your Doctor

Talk to your doctor about your risk of thyroid issues. They may recommend seeing an endocrinologist — a specialist in endocrine (hormone) disorders — to help you to better understand the risks associated with myasthenia gravis.

If you’ve already been diagnosed with a thyroid condition, your doctor can work with you to find a treatment plan that fits your symptoms, risk factors, and overall health.

Talk With Others Who Understand

MGteam is the social network for people living with myasthenia gravis and their loved ones. Members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

Are you living with myasthenia gravis? Are you experiencing any issues with your thyroid? Share your thoughts in the comments below, or start a conversation by posting on your Activities page.