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Myasthenia Gravis : Causes
   
Western Medicine Chinese Medicine
Myasthenia gravis has an overall incidence of about four cases per million. There is no racial or geographic predilection, and the disorder can occur at any age. However, there is an increased incidence in young women, especially in the third decade, and in older men in the seventh decade.

The disease is caused by the autoimmune destruction of the acetylcholine receptors on the post-synaptic membrane of the muscle fiber. Immune complexes are deposited at the post-synaptic membranes causing interference with and later destruction of the acetylcholine receptor. The communication between the nerve impulses and muscle fibers is impaired or lost and muscle weakness results.

Click here to see structure of the Neuromuscular Junction

The process that initiates the immune response is unknown, but the thymus gland appears to be critical for both the autoimmune activation and the maintenance of the activated autoimmune state. Overgrowth of the thymus gland is found in 70 per cent of myasthenic patients below the age of 40 years. In 10 per cent of patients there is a tumor of the thymus gland and the incidence of this increases with age.

There is an association between myasthenia gravis and thyroid disease, rheumatoid disease, pernicious anemia and systemic lupus erythematosus. Myasthenia gravis is sometimes caused by D-penicillamine treatment in rheumatoid disease.
 
Click here to see the causes of myasthenia gravis from a TCM perspective

In TCM, myasthenia gravis is considered to be a complex disease. Many organs or systems of the body are involved and progress of the disease varies. Manifestations of the disease do not necessarily follow a prescribed order, but depend on the pathogenic factors involved and the mechanisms affected. The causes can be classified as follows:

Exogenous causes
Invasion by exogenous pathogens leads to impaired functioning of organs and depletion of blood and vital energy (qi), contributing to the disease. TCM considers that blood belongs to yin-fluid, which is mainly responsible for providing moisture and nourishment to the tissues. The role of qi is to promote and consolidate all body functions. Deficiency in blood and qi result in inadequate supply of these essentials to the muscles, tendons and meridians and flaccidity syndrome results.

Endogenous causes
These can occur when an individual encounters emotional problems or damage by the seven modes of emotions (for example, anger damaging the liver, fear damaging the kidneys or melancholia damaging the spleen). The understanding in TCM is that the liver stores the blood that supports the tendons, and the kidneys store essence for the production of bone marrow. Both blood and essence are part of yin. If an individual's liver-yin and kidney-yin are depleted, a virtual fire is created internally causing the supply of blood and essence to become exhausted. The tendons and muscles then lose their nutrient supply and become weak and numb.

Non-exogenous/endogenous cause
This is mainly the result of an imbalanced lifestyle and includes the eating of an improper diet (too much greasy or sweet food) or excess consumption of alcohol and leads to spleen and stomach injury. Stress and chronic disease can also result in a decline in qi and body fluid and cause spleen and stomach damage. The spleen and stomach are the primary organs for digestion and absorption; they extract nutritive essence from food and use it for the production of qi, blood and body fluids. If they do not function properly, muscle weakness, drooping eyelids or breathing difficulties can develop.

Congenital factors
Inborn defects, such as weakness of the spleen and stomach, yang-deficiency of the spleen and kidneys or yin-deficiency of the liver and kidneys, can cause failure in different organs and lead to the disease.