What Is Myasthenia Gravis (MG)?
Myasthenia gravis is a rare autoimmune disease in which the immune system interferes with the transmission of nerve impulses to the muscles, especially those of the eyes, mouth, throat, arms, and legs. People with myasthenia gravis develop severe, sometimes life-threatening, weakness. They may experience drooping eyelids or double vision, as well as difficulty chewing, swallowing, talking, and breathing. The disease can progress to affect a person’s ability to control the neck and limbs.
While there is no cure for myasthenia gravis, treatment can help alleviate its symptoms. Myasthenia gravis is uncommon, affecting up to 20 out of 100,000 Americans. The disease can occur at any age, though it is most common in women under the age of 40 and men over the age of 60.
Myasthenia Gravis Classifications
Myasthenia gravis is classified according to which skeletal muscles are affected by the condition, as well as the severity of the muscle weakness. The classes of myasthenia gravis are as follows:
- I – The disease causes eye muscle weakness and possibly eye-drooping, but there is no evidence that it affects any other muscle groups.
- II – The disease causes eye muscle weakness and mild weakness of other muscles.
- IIa – The other muscle groups affected are primarily limb and/or axial muscles. Limb muscles enable movement of the arms and legs. Axial muscles support the skeleton and include muscles of the trunk of the body and muscles that move the head.
- IIb – The other muscle groups affected are primarily respiratory or bulbar muscles. Respiratory muscles are involved in breathing, and bulbar muscles are muscles of the head and neck used to chew, swallow, and speak.
- III – The disease causes eye muscle weakness and moderate weakness of other muscles.
- IIIa – The other muscle groups affected are primarily limb or axial muscles.
- IIIb – The other muscle groups affected are primarily respiratory or bulbar muscles.
- IV – The disease causes eye muscle weakness and severe weakness of other muscles.
- IVa – The other muscle groups affected are primarily limb or axial muscles.
- IVb – The other muscle groups affected are primarily respiratory or bulbar muscles. Patients may require feeding tubes without intubation.
- V – Intubation is required to open the airways and deliver oxygen.
Signs & Symptoms of Myasthenia Gravis
Signs and symptoms of myasthenia gravis may include vision problems and sometimes severe muscle weakness and fatigue. Muscle weakness can vary in severity and the type of muscles affected, and it intensifies with activity. People with myasthenia gravis may feel stronger when they first wake up, but weaker by the end of the day.
Signs and symptoms of myasthenia gravis may include:
- Drooping eyelid(s)
- Impaired vision or double vision
- Difficulty chewing and swallowing
- Impaired speech
- Distortion of facial muscles
- Difficulty breathing or shortness of breath
- Weakness of neck or limb muscles
- Difficulty moving the neck or holding up the head
- Difficulty walking
Myasthenic crisis symptoms
Myasthenic crisis occurs when the muscles that control breathing become too weak to function properly, and a ventilator is required to assist a person’s breathing. A myasthenic crisis is considered a life-threatening medical emergency that requires immediate treatment, and up to 20 percent of people with myasthenia gravis experience a myasthenic crisis at least once.
Symptoms of a myasthenic crisis vary from person to person and may include:
- Difficult breathing or shortness of breath
- Difficulty clearing saliva or phlegm
- Difficulty swallowing
- Skin around the ribs or neck pulling in while breathing
- Coughing when drinking and/or eating
- Changes in speech, such low volume or nasal speech
- Difficulty holding up the head
- Morning headaches
- Severe fatigue
- Changes in sleep patterns, such as waking up frequently
What Causes Myasthenia Gravis?
Myasthenia gravis is an autoimmune disease that occurs when the body’s immune system mistakenly attacks itself. In myasthenia gravis, the immune system interferes with the communication between the nervous system and the muscular system.
Normally, our nerve cells relay information from the brain to the muscles by releasing neurotransmitters such as acetylcholine. Muscles have receptor sites to which the neurotransmitters can bind, triggering the muscle to contract and move. Myasthenia gravis prevents neurotransmitters from binding properly, leading to muscle weakness and diminished muscle control.
Causes of myasthenia gravis include:
- Abnormal antibodies. Produced by the immune system, antibodies normally help identify disease-causing agents that enter the body. In people with myasthenia gravis, the immune system produces abnormal antibodies that block or destroy the receptor sites on the muscles, blocking communication from the brain.
- Thymus gland issues. The thymus gland is a part of the immune system that lies in the upper chest area beneath the breastbone. Some people with myasthenia gravis have tumors on the thymus gland, or the thymus gland is unusually large or has abnormalities. Researchers believe that when the thymus gland is unable to work properly because of these conditions, it is more likely to mistakenly create immune cells that are programmed to attack the muscles’ receptor sites, leading to myasthenia gravis.
In rare cases, myasthenia gravis occurs in a temporary form in newborns who have mothers with myasthenia gravis. The antibodies that cause myasthenia gravis can use the placenta to move from the mother’s body to the baby. This is known as neonatal myasthenia gravis, and with prompt treatment, the newborns can recover within months once the antibodies are cleared from the baby’s bloodstream.
Risk Factors for Myasthenia Gravis
Myasthenia gravis is not inherited nor is it contagious, but certain factors may increase a person’s likelihood of developing myasthenia gravis. Risk factors include:
- Age and sex. Myasthenia gravis is most common in women under the age of 40 and men over the age of 60.
- Newborns with mothers who have myasthenia gravis. Some newborns whose mothers have myasthenia gravis may develop a temporary condition called neonatal myasthenia gravis.
- Having a history and/or certain genetic markers of autoimmune disorders. Lupus, thyroid disease, or rheumatoid arthritis may increase the risk of developing myasthenia gravis.
Health complications associated with myasthenia gravis are treatable, though they can be potentially life-threatening. Complications of myasthenia gravis include:
- Myasthenic crisis. This occurs when respiratory muscles are too weak to function, and a ventilator is required to assist in breathing. This is considered a medical emergency that requires immediate treatment.
- Thymus gland tumors. In most cases, these tumors are not cancerous.
- Thyroid issues. Some people with myasthenia gravis may develop thyroid issues such as an overactive or underactive thyroid gland. The thyroid gland regulates metabolism, so this can lead to weight changes, difficulty dealing with temperature changes, and other issues.
- Autoimmune conditions. People with myasthenia gravis have an increased risk of having other autoimmune diseases, such as lupus or rheumatoid arthritis.
Trust NewYork-Presbyterian for Myasthenia Gravis Care
NewYork-Presbyterian Hospital’s neurologists and neurosurgeons work closely with other medical specialists to evaluate and treat patients with myasthenia gravis, offering comprehensive care to manage symptoms and improve quality of life. Learn more about NewYork-Presbyterian’s treatment and care services for myasthenia gravis and begin your personalized treatment plan.