What Is Myasthenia Gravis (MG)?

Myasthenia gravis, or MG, is a neurological illness marked by chronic muscle weakness and fatigue. Persons with MG face difficulties in standing, walking, talking, chewing, and swallowing. MG also causes problems with eyesight. It is a relatively rare disorder, affecting about 20 out of every 100,000 Americans, targeting especially women under the age of 40 and men older than age 60. There is no permanent cure for MG but a variety of treatments have been developed to control symptoms and slow the disease’s progress. 

Symptoms

MG primarily impacts the skeletal muscles – the ones that power physical movement and voluntary activity. This results in symptoms such as:

• Fatigue and sleepiness
• Difficulties in standing up, walking, lifting objects, and negotiating stairs
• Droopy eyelids and double vision
• Facial paralysis
• Problems talking, chewing, and swallowing
• Hoarseness
• Troubled breathing

There can be some variation in Myasthenia Gravis symptoms over time, though they tend to grow worse, if left untreated.

Causes

Myasthenia Gravis is an autoimmune disease, meaning that your body’s defenses against intrusive infection begin attacking some aspect of your internal chemistry instead. This can happen in several different ways:

• Acetylcholine blockers: The brain activates skeletal muscles by means of neurotransmitters, that is, electrochemical signals that travel the nervous system. In the most common form of MG, antibodies produced by the immune system block a neurotransmitter called acetylcholine from reaching receptor sites on the muscles. The protein tyrosine kinase, also involved in this process, is affected as well. The reduction in brain-to-muscle communication leads to a weakening of the muscles. 

• Antibody-negative MG: In this form of the disease, antibodies attack lipoprotein-related protein 4, another link in healthy brain-muscle communication. 

• Role of the thymus gland: The thymus gland, located in the upper chest, has a part in MG. It is believed to be the source of the antibodies that attack acetylcholine and other elements of muscle neurology. Adults with MG often have a larger-than-normal thymus gland or tumorous growths called thymomas.

Several risk factors increase the likelihood of MG:

• Age (women under 40 and men over 60)

• Pregnancy

• Menstrual periods

• Other forms of illness

• High levels of stress

• Certain medications, including beta blockers and some antibiotics

Diagnosis 

There are a number of diagnostic options for determining whether you’ve developed MG:

• Medical history and physical exam: Your physician will conduct a physical exam, record your symptoms, and look into your medical history. 

• Neurological exam: A series of tests involving muscle strength, muscle tone, reflexes, coordination, balance, and sense of touch will evaluate your neurological health. 

• Blood analysis: Antibodies involved in blocking muscle-receptor sites can be detected in blood tests.

• Ice-pack test: The ice-pack test is used to measure the cause and nature of droopy eyelids, which can be an early symptom of MG. 

• Edrophonium test: Edrophonium is a chemical that counteracts acetylcholine-blocking antibodies – in essence, blocking the blockers. A temporary return of muscle strength during an edrophonium test can indicate the presence of MG. 

• Repetitive-nerve stimulation: Your physician will send electrical currents through your muscles by means of small electrodes. He or she will be looking for a loss of conductivity as muscle fatigue increases. 

• Magnetic resonance imaging (MRI) and CT scans: Imaging scans of the thymus gland can provide evidence of enlargement or tumors.

Other diagnostic options include a pulmonary-function test for breathing and single-fiber electromyography for documenting declines in neuromuscular transmission. 

Treatment

The focus for treating MG is on relieving symptoms rather than offering a cure. The steps taken by your physician will depend on your age, the disease’s severity, and how rapidly it’s progressing:

Complications

There are several complications with MG. These complications include a potentially life-threatening condition that requires immediate emergency care. 

Complications include:

• Higher risk of developing autoimmune disorders.
• Myasthenic Crisis, which is a potentially fatal condition marked by difficulty breathing and muscle weakness. 

If you or a loved one experience any symptoms of myasthenic crisis, please seek immediate medical care. 

Medications

Two major types of medications are available to treat MG. Cholinesterase inhibitors such as pyridostigmine and neostigmine improve muscle neurotransmission. Corticosteroids and immunosuppressants both work to suppress immune-system response, often in combination. The side effects of these drugs can be medically problematic, limiting their usefulness. 

Intravenous Therapy

Worsening Myasthenia Gravis symptoms can be treated with intravenous therapy:

• Plasma exchange: Plasma exchange, or plasmapheresis, is a process by which the antibodies attacking your muscle receptor sites are eliminated from the bloodstream. Blood is removed from your body and divided into two parts: cells and the liquid they’re suspended in – plasma. Only the cells are returned to your body where they help to generate new plasma free of the immune agents driving the disorder. Plasma exchange carries the risk of critical side effects, including bleeding, heart arrhythmias, cramps, and plummeting blood pressure.

• Intravenous immunoglobulin: Immunoglobulin is a source of antibodies or immune agents. Receiving doses of immunoglobulin from healthy donors can counteract the negative effects of antibodies attacking the nerves. Side effects tend to be relatively mild.

• Monoclonal antibodies: Physicians will sometimes use the medications rituximab and eculizumab to combat MG, if other therapies prove ineffective.

Surgery

A surgical procedure might be required to excise a tumor from the thymus gland. A second possibility is removal of the entire thymus gland, called a thymectomy. The benefits of surgery in treating MG can take years to become apparent. Video- and robot-assisted thymectomies are increasingly common. 

Prognosis

Myasthenia gravis prognosis varies depending on the person, medical history, and severity of the condition. Some individuals only experience mild symptoms. Others experience more severe symptoms and may eventually require the use of a wheelchair. Early intervention and treatment can often slow the progression of the disease.