Myasthenia gravis is marked by extreme tiredness and weakness of the muscles in the body. It is caused by lapse of communication between the nerves and the muscles. It is a type of autoimmune disorder wherein the body’s own immune system will attack the muscles causing muscular weakness. This disorder can cause blurred vision, unstable gait and difficulty in swallowing in addition to weakness in various parts of the body.
It is a chronic disorder requiring prolonged treatment of immunosuppressant agents. Though the disease cannot be cured still the symptoms can be managed by effective medications. The symptoms will not be of same degree for all people and the intensity of weakness of the voluntary muscles varies considerably. Often, the symptoms of weakness will be peak for some period followed by remission.
Muscular weakness is the major sign of myasthenia gravis but the symptoms range from mild to severe. There are remission periods where there will not be any symptoms. Certain types of muscle groups are largely affected in this disease. If the eye muscles are affected it can cause blurred vision, drooping of eyelids and double vision. For most of the people affected with myasthenia gravis blurred vision is common. Double vision can be either horizontal or vertical and the disease slowly progresses.
When the throat and face muscles are affected, it can alter the normal speech and cause difficulty in chewing/swallowing. Choking is common when the throat muscles get weakened. In some cases, it can change the normal facial expression of the concerned person. For some people, the neck muscles and the muscles of arms and legs are affected causing difficulty in walking and pain in moving their hands.
The concept of body movement is based on the signals received and sent by neurotransmitters. Nervous system has good communication with the muscular system and they release certain chemicals that are required by the concerned muscle. These chemicals are known as neurotransmitters which fit into the receptor sites of the muscle. But in the people with myasthenia gravis, the body’s own immunity will destroy such receptor sites that can receive special chemical called acetylcholine. Since there is no receptor site in the muscle system to receive acetylcholine the muscles may not receive enough nerve signals causing weakness. Antibodies released by the immune system will arrest the function of protein by name tyrosine kinase which is important in the formation of nerve muscular junction. When this happens, it can lead to muscular weakness or myasthenia gravis.
It is believed that thymus gland also plays a role in causing myasthenia gravis. Thymus gland is found in the chest region is responsible for producing antibodies that impairs the function of acetylcholine. In childhood, the size of thymus gland is small resulting in less secretion of antibodies. But in adults the gland becomes large and produces more of antibodies that block acetylcholine leading to myasthenia gravis. There are people who develop tumors in the thymus gland called thymomas but they are not cancer causing agents and are harmless.
For some people the function of certain lipoprotein which is responsible for releasing antibodies is blocked causing this disease. In rare cases, myasthenia gravis can be hereditary also passing the autoimmune disorder from the parents to the child. Certain type of illness, extreme tiredness, stressful events and living in extreme heat weather can also trigger myasthenia gravis. Certain medications like quinidine gluconate (beta blockers) and certain anesthetics may also trigger muscular weakness.
In rare cases, myasthenia gravis can become dangerous if the muscles of the throat become weak affecting the breathing process. In such cases, artificial ventilation is to be provided for the patient on emergency basis. Thymus tumors called thymomas are common in people having myasthenia gravis but they are usually harmless. In some cases the function of thyroid gland can get affected due to myasthenia gravis causing hypothyroidism or hyperthyroidism. Finally people with this disease are more likely to get other autoimmune disorders like arthritis or lupus.
Risk Factors :
Myasthenia gravis can affect anyone of any age group. Often it is seen in women (age group of 40-45) and men (60-70) for no apparent reason. Infants that inherit certain antibodies that block acetylcholine from the mother will have only temporary symptoms and the muscular weakness will disappear on its own after few months. In very rare cases, the infants may carry congenital myasthenic syndrome caused by defective genes.
The doctor will look for the above signs of muscular weakness by collecting the medical history of the patient. He would request for various neurological tests to check reflex reaction, coordination and muscular balance. The diagnosis can be confirmed through endrophonium test in which specific chemicals are injected into the bloodstream. If the patient feels sudden improvement in the symptoms then it indicates myasthenia gravis. Endrophonium chloride that is injected would block the enzyme that disrupts the function of acetylcholine resulting in good transmission of nerve signals.
Droopy eyelids can be tested by ice pack test to confirm the diagnosis. Blood culture is done to check the presence of abnormal antibodies released by immune system. In some people nerve stimulation test will be done several times to confirm the disease. Muscle fiber can be tested through single fiber electromyography. In case the doctor is suspicious about thymus tumor he may order for CT scan to check the thymus gland.
Treatment is given on the basis of severity of the symptoms and the part of the body affected. In many cases medications will be combined with therapeutic procedures for getting relief from symptoms. Medications like pyridostigmine (cholinesterase inhibitors) are given for achieving improved communication between the muscles and nerves. It improves muscle strength and contraction gradually. Corticosteroids like prednisone are prescribed for restricting the activities of immune system that produces unwanted antibodies. Both these medicines can have some adverse effect and should be taken under the supervision of doctor. In severe cases immunosuppressant drugs like azathioprine, mycophenolate mofetil and cyclosporine are prescribed.
- Therapy :
During plasmapheresis therapy blood travels through a special device that filters the unwanted antibodies that block the nerve signals. In the result nerve signals are properly transmitted to the receptor sites of the muscles. This process is similar to that of dialysis but the effects will not last for long. For this reason, this procedure has to be repeated frequently. After some months, it becomes difficult to trace the vein for the therapist. For some people, the doctor will insert a catheter into the chest region for doing plasmapheresis. It can cause hypertension and abnormal heartbeat and some people can develop allergy.
In another therapy known as immunoglobulin therapy IVIg normal antibodies are injected into the bloodstream for streamlining the immune system. Eventually they may stop producing unwanted antibodies that blocks acetylcholine. This procedure is effective and does not have many side effects. Surgery is done if the person develops tumors in thymus gland. Thymectomy is doen to remove the thymus gland entirely from the body.
This will give you relief from the symptoms for the rest of your life. During this surgery, the breast bone is cut open centrally to remove the thymus gland. In can be done through minimal incisions by making a small cut in the neck portion and by using video endoscope thymus gland can be removed. Surgery is the last option for myasthenia gravis and doctors may perform it after considering several factors like age, health condition, intensity of symptoms and any other complications.
Lifestyle Changes :
Eating small meals several times a day can improve your muscle strength. You need to chew the food properly before swallowing it. You can avoid falling down by taking precautions while using bathrooms and sidewalks. Wherever possible you can make use of electric devices instead of spending your energy. For people having drooping eyelids and double vision, wearing an eye patch can be useful. Avoid stressful events and practice yoga and meditation regularly.
With proper treatment and therapy this disease can be managed effectively. You can lead normal life by managing muscular weakness. For some people remission can occur even after thymectomy surgery.