What is Myasthenia Gravis?
MYASTHENIA GRAVIS (MG) is a chronic disabling autoimmune neuromuscular disease of severe, crippling weakness. MG results from a defect in transmission of the nerve impulse to the nerve-muscle junction. In other words, the nerve is healthy and the muscle is healthy, but the signal from the nerve does not reach the muscle effectively, with the result that the muscle does not contract or function as usual.
MG is characterized by weakness of voluntary muscles that are joined to the skeleton and are responsible for movement (and not the involuntary muscles – those in the gut and internal organs of the body). The hallmark of myasthenia gravis is muscle fatigue. Muscles become progressively weaker during periods of activity and improve after periods of rest.
MG can affect any muscle, but the muscles that control eye and eyelid movement, facial expression, and swallowing are most often affected. In some people, the first symptom is weakness of the eye muscles. In others, having a hard time swallowing, talking, and breathing can be the first signs. Different people have different levels of muscle weakness.
Symptoms may include:
* Drooping of one or both eyelids
* Blurred or double vision
* Problems walking (legs can suddenly give way)
* Weakness in arms, hands, fingers, legs, and neck
* Change in facial expression
* Having a hard time chewing food and swallowing
* Trouble speaking clearly (words may be slurred)
* Shortness of breath (feeling like you can’t get enough air)
The onset of the disorder may be sudden or very gradual and there is a huge variation between one person and another. Because the symptoms are not immediately recognized as MG and because of the variation between one person’s disease and another, often MG is misdiagnosed as something else (like MS or ALS) or missed completely in which case patients may be told “it’s all in your head”.
For this reason, it is probable that the prevalence rate is actually higher than the currently estimated 70,000 people in the USA.
In myasthenic crisis a paralysis of the respiratory muscles occurs, necessitating assisted ventilation to sustain life. In patients whose respiratory muscles are already weak, crises may be triggered by infection, fever, an adverse reaction to medication, or emotional stress. Since the heart muscle is stimulated differently, it is never affected by MG.
In more than half the people who develop myasthenia gravis, their first signs and symptoms involve eye problems, such as:
- Drooping of one or both eyelids (ptosis)
- Double vision (diplopia), which may be horizontal or vertical
- Blurred vision, which may come and go
Face and throat muscles
In about 15 percent of people with myasthenia gravis, the first symptoms involve face and throat muscles, which can cause difficulties with:
- Speaking: speech may be very soft, or slurred or sound nasal, depending upon which muscles have been affected.
- Swallowing: may choke very easily, which makes it difficult to eat, drink or take pills. In some cases, liquids being swallowed may come out the nose.
- Chewing: muscles used for chewing may wear out halfway through a meal, particularly if eating something hard to chew, such as steak.
- Facial expressions: family members may note that a person with MG has “lost their smile” if the muscles that control facial expressions are affected.
Arm and leg muscles
Myasthenia gravis can cause weakness in arms and legs, but this usually happens in conjunction with muscle weakness in other parts of the body — such as eyes, face or throat. The disorder usually affects arms more often than legs. However, if it affects legs, a person may ‘waddle’ when they walk.