Myasthenia gravis is a neuromuscular disorder that affects one in 5,000 people, according to Juel and Massey. The onset of myasthenia gravis can begin at any age, though Juel and Massay noted that juvenile myasthenia gravis is rare. Young women and older men tend to have the disorder more often.
This disorder is a type of autoimmune disorder, which means the patient’s immune system attacks healthy tissue. Normally, the white blood cells protect the human body from foreign substances that cause harm, such as viruses, cancer cells, bacteria and toxins.
But when a patient has an autoimmune disorder, the immune system cannot differentiate between healthy cells and harmful foreign substances. In myasthenia gravis, the symptoms result from a disruption of acetylcholine transmission between the nerve and muscles. The patient’s immune system alters, destroys or blocks acetylcholine receptors at the neuromuscular junction, causing problems with muscle contraction.
The exact reason why the immune system would attack healthy tissue is not known, but several theories exist. MedlinePlus noted that one theory is that the changes in the immune system are triggered by a drug, virus or bacterium. A specific theory on the cause of myasthenia gravis is the involvement of the thymus gland in the damage to the acetylcholine receptors.
The MayoClinic.com explained that the thymus gland, which is part of the immune system, may either trigger the production or help maintain the production of the antibodies that affect the acetylcholine receptors in the neuromuscular junction.
Some patients who have myasthenia gravis have an abnormally large thymus gland. By comparison, adults without myasthenia gravis have a small thymus gland. Other patients with myasthenia gravis have a tumor of the thymus gland, though they are usually not cancerous.
Certain factors may worsen myasthenia gravis. These can include external factors, such as extreme heat and illness. Patients who are feeling fatigued or are under stress can have a worsening of the disorder.
Some medications can also worsen myasthenia gravis.