Myasthenia gravis

Definition

Myasthenia gravis is a neuromuscular disorder. Neuromuscular disorders involve the muscles and the nerves that control them.

Alternative Names

Neuromuscular disorder - myasthenia gravis

Causes

Myasthenia gravis is a type of autoimmune disorder. An autoimmune disorder occurs when the immune system mistakenly attacks healthy tissue. Antibodies are proteins made by the body's immune system when it detects harmful substances. Antibodies may be produced when the immune system mistakenly considers healthy tissue to be a harmful substance, such as in the case of myasthenia gravis. In people with myasthenia gravis, the body produces antibodies that block the muscle cells from receiving messages (neurotransmitters) from the nerve cells.

In some cases, myasthenia gravis is linked to tumors of the thymus (an organ of the immune system).

Myasthenia gravis can affect people at any age. It is most common in young women and older men.

Symptoms

Myasthenia gravis causes weakness of the voluntary muscles. These are muscles that you can control. Autonomic muscles of the heart and digestive tract are usually not affected. The muscle weakness of myasthenia gravis worsens with activity and improves with rest.

This muscle weakness can lead to a variety of symptoms, including:

• Breathing difficulty because of weakness of the chest wall muscles
• Chewing or swallowing difficulty, causing frequent gagging, choking, or drooling
• Difficulty climbing stairs, lifting objects, or rising from a seated position
• Difficulty talking
• Drooping head and eyelids
• Facial paralysis or weakness of the facial muscles
• Fatigue
• Hoarseness or changing voice
• Double vision
• Difficulty maintaining steady gaze

Exams and Tests

The health care provider will perform a physical exam. This includes a detailed nervous system (neurological) examination. This may show:

• Muscle weakness, with eye muscles usually affected first
• Weakness usually fluctuates and gets worse with exercise
• Normal reflexes and feeling (sensation)

Tests that may be done include:

• Blood test to check for acetylcholine receptor antibodies associated with this disease
• CT or MRI scan of the chest to look for a tumor
• Nerve conduction studies to test how fast electrical signals move through a nerve
• Electromyography (EMG) to test the health of the muscles and the nerves that control the muscles
• Pulmonary function tests to measure breathing and how well the lungs are functioning
• Edrophonium test to see if this medicine reverses the symptoms for a short time

Treatment

There is no known cure for myasthenia gravis. Treatment may allow you to have periods without any symptoms (remission).

Lifestyle changes can often help you continue your daily activities. The following may be recommended:

• Resting throughout the day
• Using an eye patch if double vision is bothersome
• Avoiding stress and heat exposure, which can make symptoms worse

Medicines that may be prescribed include:

• Neostigmine or pyridostigmine to improve communication between the nerves and muscles
• Prednisone and other drugs (such as azathioprine, cyclosporine, or mycophenolate mofetil) to suppress the immune system response if you have severe symptoms and other medicines have not worked well
• Other immunological therapies target specific immune cells or inflammatory response

Crisis situations are attacks of weakness of the breathing muscles. These attacks can occur without warning when either too much or too little medicine is taken. These attacks usually last no longer than a few weeks. You may need to be admitted to the hospital, where you may need breathing assistance with a ventilator.

A procedure called plasmapheresis may also be used to help end the crisis. This procedure involves removing the clear part of the blood (plasma), which contains the antibodies. This is replaced with donated plasma that is free of antibodies, or with other fluids. Plasmapheresis may also help reduce symptoms for 4 to 6 weeks and is often used before surgery.

A medicine called intravenous immunoglobulin (IVIg) may also be used

Surgery to remove the thymus (thymectomy) may result in permanent remission or less need for medicines, especially when there is a tumor present.

If you have eye problems, your doctor may suggest lens prisms to improve vision. Surgery may also be recommended to treat your eye muscles.

Physical therapy can help maintain your muscle strength. This is especially important for the muscles that support breathing.

Some medicines can worsen symptoms and should be avoided. Before taking any medicine, ask your doctor whether it is OK for you to take it.

Support Groups

You can ease the stress of illness by joining a myasthenia gravis support group. Sharing with others who have common experiences and problems can help you not feel alone.

Outlook (Prognosis)

There is no cure, but long-term remission is possible. You may have to restrict some daily activities. People who have only eye symptoms (ocular myasthenia gravis), may develop generalized myasthenia over time.

A woman with myasthenia gravis can get pregnant, but careful prenatal care is important. The baby may be weak and require medicines for a few weeks after birth, but usually will not develop the disorder.

Possible Complications

The condition may cause life-threatening breathing problems. This is called a myasthenic crisis.

People with myasthenia gravis are at higher risk for other autoimmune disorders, such as thyrotoxicosis, rheumatoid arthritis, and systemic lupus erythematosus (lupus).

When to Contact a Medical Professional

Call your health care provider if you develop symptoms of myasthenia gravis.

Go to the emergency room or call 911 or the local emergency number if you have breathing difficulty or swallowing problems.

References

Chang CWJ. Myasthenia gravis and Guillain-Barré syndrome. In: Parrillo JE, Dellinger RP, eds. Critical Care Medicine: Principles of Diagnosis and Management in the Adult. 5th ed. Philadelphia, PA: Elsevier; 2019:chap 61.

Guptill JT, Sanders DB. Disorders of neuromuscular transmission. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley's and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 108.

Sanders DB, Wolfe GI, Benatar M, et al. International consensus guidance for management of myasthenia gravis: executive summary. Neurology. 2016;87(4):419-425. PMID: 27358333 pubmed.ncbi.nlm.nih.gov/27358333/.