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Other Autoimmune Diseases and Myasthenia Gravis

Reviewed by: HU Medical Review Board | Last reviewed: March 2021

Myasthenia gravis (MG) is an autoimmune disease. This means that the body’s immune system can no longer tell the difference between healthy cells and unhealthy invaders like cancer or germs.

Because it cannot tell the difference, the immune system of a person with MG begins to attack healthy spots on the muscle that receive communication signals from nerves. This causes the muscles to become weak and tire easily.

Like many other autoimmune conditions, research shows that people who develop MG may have inherited genes that make them more likely to develop autoimmune conditions.1

Doctors also know that people with MG are at higher risk of already having or developing other autoimmune conditions. This could be another sign that genes play a role in who develops myasthenia gravis.2

Worldwide, about 5 out of every 100 people have 1 or more autoimmune disorders. In people with MG, 13 to 22 out of every 100 people have a second autoimmune condition. Autoimmune conditions like lupus, multiple sclerosis, and rheumatoid arthritis are much more common than MG. Out of 100,000 people with any autoimmune condition, only 35 will have MG.3

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Autoimmune conditions that occur with MG

The autoimmune conditions that people most often have in addition to MG include:4

Conditions by type

Doctors know that certain subtypes of MG are more likely to develop certain autoimmune conditions. Some of the most common autoimmune conditions that occur at the same time as MG include:3

Autoimmune conditions by MG type

Subtype of MGOther autoimmune disorders
Ocular MGThroiditis
Generalized early-onset MGThyroiditis, lupus, type 1 diabetes, alopecia, giant cell myocarditis, myositis, red cell aplasia, autoimmune hepatitis, Sjögren’s syndrome, Addison’s disease, Guillain–Barre syndrome
Generalized late-onset MGHashimoto’s disease, lupus, multiple sclerosis
Thymoma MGLupus, Sjögren’s syndrome, autoimmune hemolytic anemia, POEMS syndrome
MuSK MGLupus, multiple sclerosis
LRP4 MGLambert Eaton myasthenic syndrome

Thyroiditis (autoimmune thyroid disease) is the most common secondary autoimmune condition that people with MG have. About 1 in 10 people with MG also have thyroiditis. Lupus occurs in between 1 and 8 out of 100 people with MG. Rheumatoid arthritis, dermato-/polymyositis, and Addison’s disease follow.3

What is thyroiditis?

With thyroiditis, or autoimmune thyroid disease, the body’s immune system attacks the thyroid gland, causing inflammation. This inflammation can cause the thyroid to be overactive (hyperthyroidism) or underactive (hypothyroidism). Hashimoto’s disease is 1 of the most common types of thyroiditis.5

Treating a secondary disease

Treatment will be different depending on the type of secondary autoimmune condition the person with MG develops. For example, lupus treatments may be quite different from rheumatoid arthritis. However, many autoimmune conditions, including MG, use steroids to control symptoms.

Having more than 1 autoimmune condition may make it harder to treat myasthenia gravis due to overlapping symptoms and the need for multiple immune system drugs.4