Myasthenia Gravis – An Autoimmune Disease

Myasthenia Gravis is an autoimmune neuromuscular disorder characterized by the weakness and fatigue of voluntary muscle groups. This disorder sometimes affects certain muscles only such as the muscles of eyes, which is called ocular myasthenia gravis; but generalized myasthenia gravis is also can be seen in many patients that affects other muscle groups also.

A study in United States shows that 20 persons out of 100,000 are becoming victim to this disease. It is not a contagious disease nor is it transferred by inheritance. It affects all groups of people; races, age or gender is not a barrier. Statistics show that it is commonly attacks younger women in 20 to 40 age groups and men in 50 to 70 age groups.

Myasthenia gravis caused the muscles to weaken slowly as the immune system attacks the receptors used for muscle contraction. Practically there is no cure for myasthenia gravis, but treatment is available for the different discomforts such as muscle weaknesses, double vision, drooping eyelids and for the difficulties with delivering speech, swallowing, breathing etc. When the disease affects the muscle groups that are related to breathing, it becomes a life-threatening condition. In women, the condition of myasthenia gravis will worsen during their menstrual period.

Myasthenia gravis is caused by a defect in the transmission of nerve impulses to muscles. A receptor is an area in a muscle to where the brain sends messages (using a chemical called acetylcholine) to do contraction. A group of muscles will have a lot of receptors for its better functioning. When you are affected by myasthenia gravis, the number of receptors will be reduced considerably (sometimes up to 80%), which affects the normal functioning of that muscle group.

The destruction of the receptors is caused by the defective actions by the antibodies because of some unknown reason. The antibodies block or destroy the receptors at the neuromuscular junction which prevents the muscle from contracting.

In some cases, this malfunction of antibodies is related to a tumor of thymus gland (thymoma) which helps to produce antibodies. Thymus gland which lies in the chest area plays an important part in the development of the immune system in the early stages of life and it will become smaller after the puberty stage of a person. 15% of the myasthenia gravis patients have tumor in their thymus.

Myasthenia gravis affects the working of the voluntary muscles such as the muscles that control eye and eyelid movement, facial expression and swallowing or chewing. When the disease becomes severe, it will affect the eye vision, speech control and the patient will feel weakness in hands, legs and neck. The usual symptoms of this disorder are:

• Double vision or blurred vision
• Indistinct speech
• Muscle fatigue and weakness in arms and legs
• Drooping eyelid
• Breathing difficulty
• Difficulty for food intake (in chewing and swallowing)
• Weak cough
• Difficulty to smile
• Difficult to lift the arm upwards
• Difficulty to rise to a stand
• Difficulty to walk up stairs

Since the weakness in the muscles is associated with many other diseases, when somebody feels a weakness in the hands or legs, he will not suspect it as the effect of myasthenia gravis. In normal case, the diagnosis of myasthenia gravis is delayed because of this reason. If the physician suspects myasthenia gravis in a patient after studying the person’s medical history and the impairment of eye movements, then he will do some other tests also for confirmation.

• Test by injecting edrophonium chloride - Injection of edrophonium chloride temporarily improves the muscle strength and this can be taken as an indication of having myasthenia gravis.
• Blood test will be done to find the presence of acetylcholine receptor antibodies in blood. Most of the myasthenia gravis patients have higher levels of antibodies in their blood.
• Nerve conduction test will be done to find about the muscle responses when the nerves are stimulated by small pulses of electricity.
• Weakness of the muscle will be tested by holding the arms out at length for a reasonable period of time.
• EMG or Single fiber electromyography used to detect the impaired nerve-to-muscle transmission. Muscle fibers of a patient having myasthenia gravis do not respond to repeated electrical stimulation compared to the muscles of a normal person.
• Breathing strength of the patient will be measured using pulmonary function test.
• MRI or CT scan test will be done find out the presence of thymoma (tumor in thymus gland).

There is no complete cure for this disorder, but at the same time the various symptoms related to this disease can be treated successfully to get relief. Medicines used in the treatment of myasthenia gravis are for improving the muscle strength by suppressing the production of abnormal antibodies. A neurologist will decide the methods of treatment after analyzing the physical condition of the patient. Some of the treatment methods are as below:

• Drugs such as pyridostigmine, azathioprine, mycophenolate and cyclosporine etc. are used to stimulate the receptors and to suppress the immune system.
• In severe cases, the anti-body containing plasma will be replaced with antibody-free plasma and this treatment is called plasmapheresis.
• If the thymus gland is affected by tumor, surgery (thymectomy) will be conducted to remove this gland.
• If the patient has breathing difficulties, hospital admission is necessary and the patient should be placed on a respirator temporarily.
• Sometimes antibiotics also will be used if some infection occurs in this condition.

As in the case of the treatment, there is no sure way to prevent myasthenia gravis. But if you have this disorder, you can take some precautionary measures to control or to avoid more severe condition by observing the following guidelines:

• If you have infections, treat the infections by taking proper antibiotics.
• Keep your surroundings in a hygienic condition and avoid contacting sick people.
• Avoid overexertion.
• Do not live in very hot or in very cold situation.
• Take professional help to manage stress.

Treatment for myasthenia gravis improves the muscle weakness in many patients and they can return to their normal lives. In some cases the patients can even discontinue their drugs intake after the recovery. Technological advances and advanced researches are now helping for the accurate diagnosis of the disease and for the better management of the disorder.