Literally meaning "grave muscle weakness" in Latin and Greek, myasthenia gravis is a chronic autoimmune neuromusuclar disease characterized by varying degrees of weakness in the skeletal, or voluntary, muscles of the body.
With the therapies available today, most people who suffer from this disease are able to enjoy a normal life span.
Causes of Myasthenia Gravis
This neuromuscular disease is the result of a defect in the transmission of nerve impulses to the muscles in the body. When normal communication between the muscle and the nerve is interrupted at the place where the nerve cells connect with the muscles they control (called the neromuscular junction), this condition can occur.
When impulses normally travel down the nerve, a neurotransmitter substance called acetylcholine is released in the nerve endings. A muscle contraction is generated when acetylcholine travels from the neuromuscular junction and binds to acetylcholine receptors.
In individuals with myasthenia gravis, the receptors for acetylcholine are blocked, altered or destroyed by antibodies. This prevents the muscle contraction which should be taking place. The body's immune system produces these antibodies. Thus, this condition is an autoimmune disease because the immune system is mistakenly attacking itself instead of protecting the body from foreign organisms.
The muscles most frequently affected by myasthenia gravis are those that control facial expression, swallowing, and eye and eyelid movement, although this disease can affect any voluntary muscle. This disorder may present itself suddenly and often the symptoms are not properly diagnosed in the beginning of the illness.
In many people, weakness of the eye muscles is the first noticeable symptom. Others may find the onset brings slurred speech or difficulty in swallowing. The amount of muscle weakness caused by this disease varies greatly, ranging from ocular myasthenia (a form which is localized and limited to eye muscles) to a form in which many muscles are affected, sometimes including those that control a person's breathing.
The symptoms can also vary in severity and type, and may involve:
- Ptosis - Drooping of one or both of the eyelids
- Diplopia - Double or blurred vision
- Weakness in the arms, hands, fingers, legs and neck
- Changes in facial expression
- Difficulty in swallowing
- Waddling or unstable gait
- Shortness of breath
- Impaired speech
This disease meets all the major criteria to be considered a disorder mediated by autoantibodies against the acetylcholine receptor, or AChR. These include
- Eighty to ninety percent of affected patients have the autoantibodies present in their systems
- These autoantibodies react with an antigen, specifically the acetylcholine receptor
- The disease can be passively transferred to an animal model through the autoantibodies, producing a clinical condition which is similar to the original case
- A model disease is produced in other species by repeated injection of the human antigen
- Clinical improvement is noticeable when a reduction in the autoantibody levels occurs
Most individuals suffering from myasthenia gravis can significantly improve their muscle weakness with proper treatment and lead normal or close to normal lives. In some patients, this condition may go into remission (either temporarily or permanently). The muscle weakness disappears completely in some cases, allowing the discontinuation of the medications.
The goal of thymectomy is stable, long-lasting or complete remission and about 50 percent of the people who undergo this procedure see this occur. Respiratory failure due to the severe weakness caused by myasthenia gravis is present in a few cases, requiring immediate emergency medical care.
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