Myasthenia gravis is less common disease that has a large negative impact on the patient’s quality of life and its severe forms may be even life-threatening.
Myasthenia gravis is an autoimmune disease such as type 1 diabetes, lupus erythematosus, multiple sclerosis, ankylosing spondylitis, psoriasis and many others. There is reported more frequent simultaneous occurrence of myasthenia gravis and autoimmune skin disease known as pemphigus. Such autoimmune diseases occur because of an aggressive behavior of our own immune system, which begins to attack our own cells or tissues. In case of myasthenia, the target area is the neuromuscular junction, i.e. the point of functional connection between nerve and muscle fibers. The reason of such immune system disorder is unknown, but it is assumed to be a combination of a genetic predisposition and some common viral infection.
The neuromuscular junctions are complex structures that serve as connection between motoric nerve fibers and muscles allowing proper locomotion. If we desire to carry out a movement, the information about the movement is delivered from the brain to the spinal cord and out of there through peripheral nerves to the neuromuscular junctions of the particular muscles. Neuromuscular junctions let out a substance known as acetylcholine that irritates the muscle fibers causing their contractions. Hence, the neuromuscular junction is able to transform the electric signals to muscle contractions.
The immune cells begin to produce antibodies acting aggressively against our own tissues that are called autoantibodies. These autoantibodies invade the junction and bind to muscle receptors that are also used by acetylcholine molecules. Thus, acetylcholine molecules can not properly function causing disruption of transmitting signals from nerve to the muscles.
Here we see the neuromuscular junction, acetylcholine molecules are marked in blue
and antibodies are marked in green, that bind to acetylcholine receptors and block them.
The symptoms are based on the above mentioned mechanism of the disease. The muscles do not respond properly to neural stimulation causing muscle weakness, muscle paralysis and extreme fatigue. The affected persons have to rest frequently and they are unable to work harder. The symptoms fade away at rest, but the relief is only temporary. The patients have often a slurred speech due to paralysis of facial muscles and the weakness of eye muscles leads to double vision. The worst complication is the fatigue of respiratory muscles, which can cause shortness of breath or even suffocation.
The diagnosis is probable when the above mentioned symptoms are present. The patient should be examined by a neurologist and electromyography (EMG) to evaluate the nerve-muscle signal conduction. Serological examination of a blood sample allows finding the autoantibodies.
It is not possible to prevent the disease, but it is at least possible to prevent the bouts of extreme weakness that could lead to failure of respiratory muscles. The patient needs a lot of rest, avoid physical exertion and he must not attempt to try to overcome the fatigue by physical exercise, which could kill him easily. Any patient with myasthenia gravis must inform the anesthetist about his condition before any intervention demanding general anesthesia.
We use medications such as acetylcholinesterase inhibitors that reduce the breakdown of acetylcholine and give its molecules a chance to work longer. However, these drugs treat rather the symptoms than the disease. Surgical intervention is often very effective as it has been found out that the antibodies are often formed most immune cells in the thymus. Thymus is an organ of the immune system located in the neck and its removal is often related to disappearance of the myasthenia symptoms.
In acute condition, plasmapheresis may be used. This is a blood-cleansing method that moves the blood through a special extracorporeal device, which can sort out the antibodies. It is a very potent, but a short-time solution.