In rare cases, the heart muscle may be targeted by myasthenia gravis (MG). Heart failure, arrhythmia, myocarditis (inflammation of the heart), and death may occur when myasthenia gravis affects the heart muscle.1,2
The immune system is built to attack foreign invaders such as viruses, bacteria, fungi, and cancer cells. However, sometimes the immune system overreacts and attacks healthy tissue or cells in the body.
When this happens it is called an autoimmune disorder (“auto” means body). MG is a rare autoimmune disease where the body creates antibodies that attack certain muscles in the body. Other more common autoimmune disorders include rheumatoid arthritis, multiple sclerosis, and lupus.
In myasthenia gravis, these antibody attacks leave some muscles groups weak when used, including:1
- Eye muscles
- Face, head, and neck muscles
- Arm and leg muscles
- Breathing muscles
Risk factors
Certain people with myasthenia gravis are more likely to develop heart disease. This includes:2
- People over age 60 with severe MG
- People with a thymoma (tumor on the thymus gland)
- People with anti-Kv1 antibodies
Less than half of all people with MG have antibodies that target heart muscle. Almost all people with MG who have a thymoma will have antibodies that attack the heart. However, only about 1 out of 10 people with MG have a thymoma, so this is a rare complication.1,2
How MG and heart disease are linked
Eight out of 10 people with myasthenia gravis have AChR antibodies. These antibodies do not bind to the heart muscle and cause problems.1
A few people with MG will have a thymoma (a tumor on the thymus gland) and anti-titin, anti-ryanodine receptor antibodies (anti-RyR), or anti-Kv 1.4 antibodies (KCNA4 antibodies). These antibodies are the ones that are linked to possible inflammation and damage to the heart. Myocarditis, or inflammation of the heart muscle, happens in about 4 out of 10 people with these kinds of antibodies. Again, this is a rare complication of MG.2
Problems like myocarditis, heart failure, and arrhythmias (irregular heartbeat) usually develop between 1 and 17 years after MG symptoms first begin. Some cases of MG-related heart disease can be reversed, while others cannot.2
Overlapping symptoms
Some of the signs of heart disease and myasthenia gravis overlap. This can make it hard to diagnose someone correctly. Fatigue, trouble breathing, and weak muscles are all symptoms of both conditions, especially in older people. More research is needed to help doctors understand MG and its impact on the heart.2
Treatment
Myasthenia gravis may be treated with steroids and other drugs that target the immune system if acetylcholinesterase inhibitors do not control the symptoms. Steroids have several well-known side effects that may impact the heart. For instance, steroids may raise blood pressure, blood sugar levels, and cause weight gain.2,3
People with MG may have more heart problems after surgery than other people and need close monitoring to protect them from this complication.2