If you’re living with myasthenia gravis, you may be more likely to develop certain autoimmune conditions. Doctors and researchers believe that many autoimmune disorders share underlying causes, which can lead to co-occurring conditions.

In this article, we’ll cover conditions that you may develop alongside your myasthenia gravis and the symptoms to look out for. We’ll also discuss how your doctor may rule out Lambert-Eaton myasthenic syndrome (LEMS), another autoimmune disorder that looks very similar to myasthenia gravis.

Comorbidities of Myasthenia Gravis

“Comorbid conditions” or “comorbidities” refers to conditions that occur alongside myasthenia gravis. It’s important to note that these conditions don’t necessarily develop as a result of myasthenia gravis — they may simply happen at the same time. Since myasthenia gravis is an autoimmune disorder, many comorbidities are other autoimmune conditions.

1. Thymoma

The thymus is a key part of your immune system — this gland makes and trains specialized cells known as T cells. Normally, your thymus gland grows during childhood while producing your T cells. As you reach puberty, it stops growing and is slowly replaced with fat over time.

Researchers have found that people with myasthenia gravis still had an enlarged thymus, even as adults. Immune cells can become trapped in the tissue, leading to a type of tumor known as a thymoma. Between 10 percent and 15 percent of those with myasthenia gravis have a thymoma. Researchers have also reported that 15 percent to 40 percent of people with a thymoma have myasthenia gravis.

In most cases of myasthenia gravis, thymomas are harmless but have the potential to eventually become cancerous. Thymomas tend to grow slowly and usually don’t spread outside the thymus. On the other hand, thymic carcinomas (cancerous tumors) are more aggressive and spread quickly.

Most people don’t notice any signs of a thymoma until it begins affecting organs in the chest. Tumors can squeeze on the veins carrying blood from your body to your heart. Symptoms of a thymoma include:

• Chest pressure or pain
• Trouble swallowing
• Persistent cough
• Weak, raspy void
• Shortness of breath
• Headache
• Dizziness
• Swollen face, neck, arms, or hands

2. Autoimmune Thyroid Disease

The thyroid (not to be confused with the thymus) belongs to the endocrine system, which controls your body’s hormone levels. This butterfly-shaped gland sits at the base of your throat and plays an important role in energy metabolism.

Studies show that people with myasthenia gravis are more likely to have thyroid diseases compared with the general population. A 2020 study found that 18.4 percent of people with myasthenia gravis also had thyroid disease, compared to just 4 percent of those without myasthenia gravis. Overall, people with myasthenia gravis are 2.36 times more likely to develop thyroid disease. Myasthenia gravis also shows up in 0.2 percent of those with autoimmune thyroid disease.

Graves’ disease is a type of autoimmune thyroid disease that causes hyperthyroidism. This means the thyroid makes too much thyroid hormone, leading to problems with the skeletal muscles, heart, eyes, and liver.

In Graves’ disease, the immune system mistakenly makes autoantibodies or proteins that bind to thyroid tissue. They cause an overproduction of thyroid hormone, leading to symptoms like:

• Fast heartbeat
• Weight loss
• Excessive sweating
• Nervousness or shakiness
• Increased appetite
• Goiter (enlarged thyroid)
• Muscle weakness
• Mood swings and anxiety

Another type of autoimmune thyroid disease is Hashimoto’s thyroiditis. With this disease, hypothyroidism (an underactive thyroid) can cause fatigue, weight gain, and a slow heart rate. It’s possible, though less common, for people with myasthenia gravis to develop Hashimoto’s thyroiditis.

3. Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disorder that affects the joints, eyes, skin, and lungs. People with RA have autoantibodies that attack the lining of the joints, causing inflammation and swelling. The most common symptom is warm, swollen, and tender joints that are stiff in the morning.

Overall, researchers believe that from 1 percent to 4 percent of people with myasthenia gravis have rheumatoid arthritis. One study from Taiwan followed people with myasthenia gravis, some of whom were treated with a thymectomy (surgery to remove the thymus). They found that people who had a thymectomy were at an increased risk of developing RA, along with other autoimmune disorders affecting the joints.

Another large study found that people with RA seem to be three to four times more likely to develop myasthenia gravis than the general population.

4. Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that causes inflammation throughout the body. The most common form of lupus, SLE can affect the skin, joints, kidneys, and lungs, leading to symptoms such as:

• Joint pain and swelling
• Fatigue
• Increased sensitivity to the sun
• A butterfly-shaped rash on the nose and cheeks
• Abdominal pain
• Headaches
• Pain while breathing
• Fever

Myasthenia gravis and SLE share similar factors — for example, people with either condition can have an abnormally large thymus. Both myasthenia gravis and SLE also involve autoantibodies. Studies show that SLE is associated with an increased risk of myasthenia gravis. One report followed 380 people with SLE and found that 0.25 percent developed myasthenia gravis — a small proportion but much higher than that of the general population (0.02 percent).

5. Sjögren’s Syndrome

Another condition that can occur alongside myasthenia gravis is Sjögren’s syndrome. This autoimmune disorder affects the glands responsible for making tears and saliva. As a result, the most common symptoms of Sjögren’s syndrome are dry eyes and mouth.

Small case reports of a few dozen people have found that it’s possible to have both myasthenia gravis and Sjögren’s syndrome, though these comorbidities seem to be rarely reported in scientific literature. Some researchers believe this is because Sjögren’s symptoms can be overlooked by neurologists (doctors who specialize in brain and nervous system disorders).

Similar Conditions to Myasthenia Gravis

When doctors run tests to diagnose myasthenia gravis, they also look for other conditions to rule out. This process — known as differential diagnosis — can be difficult if your myasthenia gravis symptoms overlap with those of similar conditions.

6. Lambert-Eaton Myasthenic Syndrome

Your doctor may take extra steps to rule out LEMS, an autoimmune disease that attacks the neuromuscular junction (NMJ). In the NMJ, muscles and nerves send neurotransmitters (chemical messengers) to communicate with one another. One chemical messenger is acetylcholine, which signals muscles to contract.

In myasthenia gravis, autoantibodies attack the acetylcholine receptors (AChRs) in the muscles, preventing them from using the messenger. Without acetylcholine, the muscles can’t contract, which is why people with myasthenia gravis experience muscle weakness. Common symptoms of myasthenia gravis include diplopia (double vision), ptosis (drooping eyelids), and weakness in the neck, arms, and legs.

In LEMS, the immune system attacks specialized transporters known as voltage-gated calcium channels (VGCCs) in the muscle nerves. These channels are responsible for releasing acetylcholine from the nerve endings to the muscles. Without enough channels, the muscles can’t receive enough acetylcholine, and muscle dysfunction and weakness occur.

Since myasthenia gravis and LEMS symptoms can look very similar, doctors need to perform tests to make a final diagnosis. Antibody testing lets doctors know which autoantibodies you may have. People with myasthenia gravis may have one of three types of antibodies:

• AChR
• Muscle-specific kinase (MuSK)
• Low-density lipoprotein receptor-related protein 4 (LRP-4)

On the other hand, 85 percent to 90 percent of people with LEMS have autoantibodies targeting VGCCs, according to the Muscular Dystrophy Association.

It’s also worth noting that 50 percent to 60 percent of people with LEMS also have small cell lung cancer. Doctors and researchers believe that the immune system mistakes proteins found in cancer with the calcium channels found in the nerve endings. As a result, the immune system attacks the nerve endings.

Cancer as a Complication or Cause of Myasthenia Gravis

Some studies also report that people with myasthenia gravis are more likely to develop cancer — especially outside the thymus. A large study from Sweden found that skin cancers and cancer affecting genital organs were most common.

Researchers have also found that cancer can lead to the development of myasthenia gravis. This is known as paraneoplastic syndrome. When the immune system tries to fight cancer, it accidentally makes antibodies that target the muscles, leading to myasthenia gravis.

Find Your Team

On MGteam, 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? Do you have any other conditions related to myasthenia gravis? Share your experience in the comments below, or start a conversation by posting on your Activities page.