Myasthenia gravis
Myasthenia gravis is a rare disease characterized by muscle weakness and unusual fatigue. The disease can set in at any time but usually presents in later adulthood.
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Definition & Facts
Myasthenia gravis presents with muscle weakness and an unusually rapid tiring of the muscles when used. Myasthenia gravis is neuromuscular in nature, affecting the connection of nerves and muscles and making it difficult to control muscular movement voluntarily. Over time, this inability to control muscles leads to permanent weakening of muscle response which becomes more pronounced as the disease progresses.
The disease is classified as a rare disorder, affecting fewer than 60,000 people in the United States. In very rare cases, myasthenia gravis can lead to respiratory failure due to inability to expand and contract the diaphragm, sometimes resulting in death. This prognosis is true for less than three percent of myasthenia gravis patients. Almost all cases of this disease, even those involving severe symptoms, will not be life-threatening.
Symptoms & Complaints
Those suffering from the early stages of myasthenia gravis will generally experience rapid fatigue, particularly in the arms and legs. The weakness of the legs will often lead to difficulty in walking for any length of time.
As the disease progresses, facial muscles will become involved. The lack of ability to control these muscles leads to some of the most noticeable symptoms of myasthenia gravis, which include drooping eyelids and an inability to control the muscles around the mouth. Associated symptoms of the loss of facial muscle strength include a loss of control of the muscles of the throat and eyes, which cause difficulty in swallowing and an inability to focus the eyes, respectively.
In a minority of cases, symptoms are limited to only one area of the body, most commonly the eye muscles. Myasthenia gravis symptoms will generally progress for three years before the patient's condition naturally stabilizes. Symptoms may be intermittent, especially in early stages as the muscle weakness associated with myasthenia gravis typically improves with rest.
Causes
The underlying cause of myasthenia gravis is a breakdown in the connection between the muscle and nerve cells of the body. The most usual reason for this breakdown occurring is an autoimmune response in which the body mistakenly attacks its own tissues with antibodies. In the case of myasthenia gravis, this response targets the nerve cells, causing damage that eventually leads to the lack of connection between nerves and muscles.
The cause of this response is not currently known, but cases of myasthenia gravis have a high level of correlation with unusual activity in the thymus. It is thought that this unusual thymus function, sometimes caused by tumors, may be the trigger for the production of the antibodies that attack nerve cells in connection to the muscular system.
Like many diseases, myasthenia gravis can be aggravated by many different mental and physical stressors. These include vigorous exercise, illness, exposure to extreme heat or cold and severe psychological stress.
Diagnosis & Tests
In cases where initial symptoms are mild, it is common for myasthenia gravis to remain undiagnosed until the symptoms become pronounced enough to no longer be mistaken for typical aging. The disease can be diagnosed using a variety of methods, including comprehensive reflex testing as part of a neurological examination to find muscles that are not responsive to external pressure.
Nerve conduction studies and fine motor skills testing are also usually used to help confirm the presence of myasthenia gravis. Antibody tests can also be conducted to confirm the underlying autoimmune response that causes most cases of myasthenia gravis.
Even with these tests, however, diagnosis can sometimes require longer observation of symptoms, as most of the symptoms of myasthenia gravis are also indicative of other more common disorders. It is widely believed that many cases of myasthenia gravis remain undiagnosed throughout the life of the patient due to presenting with symptoms too mild to be easily noticed.
Treatment & Therapy
There is presently no cure for myasthenia gravis, but symptoms can be managed effectively with proper treatment in most cases. Treatments that increase the strength of neurotransmitters have been shown to be effective to varying degrees in reducing the weakness typical of myasthenia gravis. Corticosteroids and immune system suppressors can also be used to limit the severity of the symptoms by preventing further progression of the autoimmune response.
In some cases, a thymectomy, or surgical removal of the thymus, can cause symptoms of myasthenia gravis to reduce in severity. However, thymectomy treatment is not always effective in the long term as symptoms can recur later on. Because the connection between the thymus and myasthenia gravis is not clearly understood, it is difficult for physicians to predict how patients will respond to a thymectomy.
Plasmapheresis, the removal and filtration of the plasma in the blood to remove antibodies, can also be effective for treating symptoms of myasthenia gravis. Because plasmapheresis only removes the existing antibodies in the blood, however, its effects are usually very temporary.
Prevention & Prophylaxis
Low potassium levels can also irritate symptoms of myasthenia gravis. The best course for the prevention of symptoms is early diagnosis of myasthenia gravis and subsequent treatment.