MYASTHENIA GRAVIS: A RARE AUTOIMMUNE DISEASE THAT AFFECTS MUSCLES

Medically Reviewed by Dr. Sony Sherpa (MBBS) - August 23, 2024

Myasthenia gravis (MG) is a chronic autoimmune condition that alters the way that nerves and muscles communicate, making a person feel weak and exhausted. It happens as a result of antibodies the immune system produces that block or kill the acetylcholine receptors on the muscle cells. Acetylcholine is a chemical messenger that transmits signals from nerve endings to muscle fibers at the neuromuscular junction. Without enough acetylcholine receptors, the muscles cannot contract normally and become weak.

As a rare condition with generalizable symptoms and a prevalence of roughly 1 in 100,000, MG can be difficult to diagnose and treat. In this article, the symptoms, causes, diagnosis, and treatment of MG are explored, alongside tips for living with the condition.

Myasthenia Gravis Symptoms

The symptoms of MG vary from person to person, depending on which muscles are affected. The most common symptoms are:

• Ptosis, or drooping eyelids, and diplopia, or double vision, are brought on by eye muscle weakening. This is called ocular myasthenia gravis.
• Weakness of the muscles in the arms, legs, neck, and trunk. This is called generalized myasthenia gravis.
• Difficulty swallowing (dysphagia), chewing, speaking, and breathing are caused by weakness of the muscles in the throat and chest. This is called bulbar myasthenia gravis.

The symptoms of MG tend to worsen with activity and improve with rest. They may also spontaneously subside or worsen over weeks and months in response to various triggers, such as stress, infection, temperature, medication, and menstruation. Those with the condition ought to pay special attention to activities or exposures that intensify muscle weakness to avoid flares.^[1]

Myasthenic Crisis is an emergency complication of MG in which the muscles in the respiratory tract become paralyzed with weakness. This is a medical emergency that can be life-threatening if not tended to promptly.

Types of Myasthenia Gravis

As touched on above, there are two main types of MG. They are ocular myasthenia gravis and generalized myasthenia gravis. These types can be further divided by the age of symptom onset, such as late-onset MG (after 50 years), early-onset MG (before 50 years), and juvenile MG (during childhood or adolescence).

Rarer subtypes include:

• Thymoma-Associated Myasthenia Gravis: A form of MG that occurs with a tumor on the thymus gland. This can affect up to 10% of those with the condition.
• Congenital Myasthenic Syndrome: A rare inherited form of MG that affects muscle function from birth.
• Transient Neonatal Myasthenia Gravis: A temporary form of MG that affects some babies born to mothers with MG.

Myasthenia Gravis Causes

The exact cause of MG is unknown. Through the course of the condition, the immune system produces antibodies that target the acetylcholine receptors on the muscle cells.

The most common antibodies produced include those targeting muscle acetylcholine receptors (AChR), muscle-specific kinase (MuSK), and lipoprotein-related protein 4 (LRP4), all of which play a prime role in muscle neurotransmission and contraction. The antibodies may be triggered by genetic factors, environmental factors, or infections.^[2]

Those with thymoma-associated MG have an abnormal growth of the thymus gland, which is a part of the immune system located behind the breastbone. The thymus gland produces T cells, which are involved in regulating the immune response. Some studies suggest that the thymus gland may play a role in the development of MG.

Is Myasthenia Gravis Hereditary?

Most types of MG are not considered to be hereditary. Genetics may play a role in the condition’s development, as people with a family history of autoimmune conditions are more likely to develop MG. Some rare forms of MG can be inherited or passed from mothers to babies, such as congenital myasthenic syndrome and transient neonatal myasthenia gravis.

Myasthenia Gravis Diagnosis

The diagnosis of MG is based on a combination of clinical signs, medical history, physical examination, and laboratory tests. Some of the tests used to diagnose MG are^[3]:

• Blood Testing: Blood tests are used to detect the presence of antibodies against acetylcholine receptors or other proteins involved in neuromuscular transmission.
• An Edrophonium Test: Edrophonium is a drug that temporarily increases the amount of acetylcholine available at the neuromuscular junction. If symptoms improve after receiving an injection of edrophonium, the test proves positive. It is mostly used to test for ocular MG.
• Electrophysiologic Testing: This tests for abnormalities in muscle neurotransmission and activity. Electromyography (EMG) is a test that measures the electrical activity of the muscles and can detect a specific pattern pertaining to MG. A repetitive nerve stimulation test may also be used that can show a decrease in muscle response after repeated stimulation of a nerve.
• Imaging tests: Computed tomography (CT) scans, magnetic resonance imaging (MRI) scans, and other imaging tests are used to show the size and shape of the thymus gland or detect any tumors or abnormalities.

Myasthenia Gravis Vs Lambert-Eaton Syndrome

Lambert-Eaton myasthenic syndrome (LEMS) and Myasthenia Gravis (MG) are both autoimmune disorders that affect the communication between nerves and muscles, causing weakness and fatigue. Despite being similar, they have unique causes and symptoms and are treated differently.^[4]

LEMS can be distinguished from MG due to:

• Having antibodies that target the voltage-gated calcium channels on nerve endings reduces the release of acetylcholine. 
• It is often associated with small cell lung cancer (SCLC), which is treated alongside the condition.
• Muscle weakness that improves with repeated use or exercise.
• Absent or reduced deep tendon reflexes.

Treatment for Myasthenia Gravis

There is no cure for MG, and treatments are geared towards managing symptoms and improving the quality of life for the affected individuals.

Treatment options for MG include:

• Medications: A specialist will prescribe medications to help reduce the production of antibodies, increase the availability of acetylcholine, or modulate the immune system. Common prescriptions include anticholinesterases like Pyridostigmine, corticosteroids such as Prednisolone, immunosuppressants including Azathioprine, and monoclonal antibodies.
• Thymectomy: Those with a thymoma are likely to benefit from surgery that removes the thymus gland. Some studies suggest that up to 27% of those with thymoma who opted for a thymectomy experienced complete remission after 5 years, showing that a cure for this type may be possible.^[5]
• Plasmapheresis: Plasmapheresis is a procedure that filters out the antibodies from the blood plasma using a machine. It can provide temporary relief for severe cases of MG or before surgery.^[6]
• Intravenous Immunoglobulin (IVIG): This treatment delivers high doses of antibodies from donated blood into the bloodstream. IVIG can help block or reduce the harmful effects of autoantibodies in MG.

Living with Myasthenia Gravis

MG is a chronic condition that requires lifelong management and monitoring. People with MG can lead normal lives with proper treatment and care.^[7]

For the best possible result, it is important for those with MG to:

• Follow your doctor’s advice and take medications as prescribed.
• Live near a hospital or medical facility that can help in the event of a myasthenic crisis.
• Avoid triggers that can worsen symptoms, such as overexertion, stress, infection, extreme temperatures, and certain drugs. Consult with a specialist before starting any new protocols, therapies, diet, or surgery.
• Rest as often as required.
• Exercise gently to keep your muscles in better shape and promote optimal neurotransmission.
• Follow a balanced diet and get enough fluids.
• Seek support from your family, friends, or support groups.

Conclusion

Myasthenia Gravis can affect any muscle, but it often affects the eye, throat, and limb muscles. MG can be diagnosed through blood tests, an edrophonium test, electrical testing, and medical imaging. Mainstay treatment includes medications that improve muscle function and block the immune system, plasmapheresis, and IVIG. Some patients may additionally benefit from a thymectomy. MG is a chronic condition that requires lifelong management and monitoring. People with MG can lead fulfilling lives with proper treatment and care.

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