Myasthenia Gravis

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What Is Myasthenia Gravis?

Myasthenia gravis, or MG, is a long-term autoimmune condition that affects communication between nerves and muscles. It causes weakness in muscles used for movements such as seeing, speaking, swallowing, walking and breathing. Weakness often increases with activity and improves with rest.

MG is not contagious and is usually not directly inherited. Symptoms and severity vary widely, but treatment can help many people manage the condition and maintain their quality of life.

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What Causes MG?

MG occurs when the immune system mistakenly disrupts signals between nerves and muscles. Antibodies block or damage proteins needed for muscles to receive messages from the nerves, causing weakness.

Common antibodies include AChR, MuSK and LRP4. Some people have no detectable antibodies and are described as having seronegative MG. The thymus gland may also play a role, although the exact cause of MG is not fully understood.

Types of MG

Ocular MG affects the muscles around the eyes and may cause drooping eyelids or double vision.

Generalized MG affects other muscles, including those used for speaking, swallowing, breathing, walking and lifting.

MG may also be classified according to antibody type, such as AChR-positive, MuSK-positive, LRP4-positive or seronegative MG.

Juvenile MG begins during childhood or adolescence. Congenital myasthenic syndromes also cause muscle weakness but are inherited conditions rather than autoimmune MG.

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How Is MG Treated?

Treatment depends on symptoms, antibody status, overall health and the muscles affected. Medicines may improve communication between nerves and muscles or reduce the immune response causing MG.

Other options can include targeted immune treatments, intravenous immunoglobulin, plasma exchange or surgery to remove the thymus gland. Treatment plans are personalized and may change over time.

Risks

Anyone can develop MG, and there is no known way to prevent it. It is not caused by lifestyle choices or physical activity.

MG is diagnosed more often in younger adult women and older men, although it can affect people of any age or sex. People with another autoimmune condition may have a higher likelihood of developing MG.

Changes in the thymus gland, including an enlarged thymus or thymoma, are also associated with MG. Genetics may affect susceptibility, but autoimmune MG is usually not directly inherited.

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Symptoms

Common symptoms include drooping eyelids, double vision, difficulty making facial expressions and weakness in the arms, legs or neck.

MG may also cause a quiet or slurred voice, difficulty chewing, choking, swallowing problems or shortness of breath. Symptoms often become worse after repeated activity and may improve after rest.

A person may feel stronger in the morning but experience more weakness later after activity. Because symptoms are not always visible, others may not realize how much MG affects daily life.

Diagnosis

Diagnosis may involve a neurological examination, blood tests for MG-related antibodies and tests that measure communication between nerves and muscles.

Chest imaging may be used to examine the thymus gland, while breathing tests may be needed if respiratory weakness is suspected. Diagnosis can take time because MG symptoms can resemble other conditions.