About Myasthenia Gravis
Myasthenia gravis is a chronic autoimmune neuromuscular disease that causes varying degrees of weakness of the voluntary (skeletal) muscles of the body.
The name is derived from Greek “muscle weakness” and Latin “grave,” and literally means “grave muscle weakness.”
It is caused by a disorder in the transmission of nerve impulses to the voluntary muscles, where normal communication between nerve and muscle is disrupted by the body’s own antibodies, which attack the receptors for acetylcholine, a neurotransmitter.
Destruction of these receptors by the body’s antibodies interferes with the body’s ability to convey information between nerves and muscles, causing the symptoms.
Signs & Symptoms
Myasthenia gravis causes progressive muscle weakness during active periods that diminishes during periods of rest.
Muscles that are most often affected by the disease control:
- The eyes.
- Eyelid movement.
- Facial expressions.
Muscles that control neck, limb movements and breathing can also be affected. Any voluntary muscle can be affected by the disorder, however.
Onset of symptoms can be sudden, and symptoms are often not immediately recognized as myasthenia gravis.
Some of the earliest and most noticeable symptoms include:
- Weakness of the eye muscles.
- Difficulty swallowing and slurred speech.
- Drooping of one or both eyelids (ptosis).
- Blurred or double vision (diplopia).
- Unstable gait.
- Change in facial expression.
- Shortness of breath.
- Difficulty swallowing.
- Impaired speech (dysarthria).
- Weakness in arms, legs, neck, and extremities.
The degree of muscle weakness varies with individuals, and can be localized to one region and can also be generalized, affecting many muscles.
How the Thymus Gland Affects Myasthenia Gravis
The thymus gland (which is located in the chest beneath the breastbone) plays an important role in your immune system development.
Starting out large in infants, it grows gradually until puberty, before getting smaller and eventually being replaced by fat as you age.
However, in adults with the disease, the thymus gland remains large and contains clusters of immune cells that indicate an active immune response.
People with myasthenia gravis sometimes develop thymomas (tumors of the thymus gland). While thymomas are usually benign, they can become cancerous.
The relationship between the thymus gland and myasthenia gravis is not completely understood at this time. Researchers believe that it may be giving incorrect instructions to developing immune cells, leading to the creation of acetylcholine receptor antibodies, and causing the autoimmune disorder.
Who Can Get Myasthenia Gravis
While most commonly occurring in young adult women (<40 years) and older men (>60 years), this disorder occurs in all ethnic groups and in both genders.
It is not directly inherited it is not contagious. Although a fetus can temporarily get it from their mother, the symptoms usually disappear within 2 to 3 months after birth.
Diagnosis is often delayed if symptoms are mild, or if muscle weakness is confined only to a few areas.
Your doctor will review your medical history and conduct neurological examinations, with particular attention to eye movements or muscle weakness.
Your doctor may perform a special blood test to find acetylcholine receptor antibodies; most patients with the disease have abnormally elevated levels of these antibodies.
The anti-MuSK antibody has also been found in some patients with myasthenia gravis who lack the acetylcholine receptor antibodies.
Some people with myasthenia gravis do not have either of these antibodies, however.
Your doctor may perform nerve conduction tests to confirm the diagnosis. Your doctor may also record muscle response through electrical nerve stimulation. If you have impaired neurotransmitter reception, it will be revealed in time through the test.
This impaired reception can also be detected through single-fiber electromyography (EMG). EMG measures the electrical potential of muscle fibers stimulated by electrical impulses. People with myasthenia gravis do not respond well to such electrical stimulation.
A neurologist will devise a treatment that is best-suited to your individual needs, with special attention to:
- Severity of the weakness.
- Your age.
- Any associated medical problems.
- Which muscles or muscle groups are affected.
There are a variety of treatments available, including:
Anticholinesterase medicines such as:
- Immunosuppressive drugs such as:
For your safety, your doctor will carefully monitor your use of these drugs.
Plasmapheresis is a procedure in which serum that contains abnormal antibodies is removed from your blood while the blood cells are preserved.
The serum can be replaced with high-dose immune globulin. This modifies your immune system by replacing abnormal antibodies with antibodies from donated blood.
Thymectomy is the surgical removal of the thymus gland. In appropriate patients, thymectomy is effective in reducing or eliminating symptoms of myasthenia and can restore balance to their immune system. If you are an adult patient, thymectomy does not weaken your immune system.
This surgery is recommended for all people who have thymoma regardless of the degree of myasthenic symptoms. In patients with myasthenia gravis and no thymoma, thymectomy may still be beneficial if symptoms become severe, if they are difficult to control with medications or if side effects of medication occur.
The surgical approach to thymectomy depends on the presence, size and location of a thymoma. If you have only myasthenia gravis or myasthenia and a small thymoma (typically < than 3cm), a video-assisted (VATS) or robotic thymectomy can be performed.
If you have larger thymomas, the standard procedure is to perform a median sternotomy to remove all thymic tissue along with the tumor.