Myasthenia Gravis
By Rear Adm. Joyce Johnson, D.O., M.A.

What is myasthenia gravis? 

Myasthenia gravis (MG) is an autoimmune disease, that is, a disease in which the body develops antibodies against itself. With MG, the antibodies are very specific to the neuromuscular junction, where the motor neuron meets muscle fiber. 

In a healthy person, a signal from the brain travels to the end of the motor neuron, where it reaches a “terminal button” that releases acetylcholine. The acetylcholine travels from the nerve to the muscle and binds with specific acetylcholine receptors at the muscle junction, resulting in muscle contraction.
In a person with mg, antibodies bind to the muscle’s acetylcholine receptors, preventing the acetylcholine from binding there and interfering with muscle contraction. The more receptors affected, the weaker the muscle will be. 

MG typically begins in women in their 20s and 30s and men in their 40s and 50s. Muscular weakness due to MG often starts with the eye muscles, in the form of ptosis or double vision. Muscle weakness also can cause difficulty speaking, swallowing, and even holding up one’s head. If the muscles of the arms and legs are affected, walking can become difficult. Although the disease might wax and wane, in about half of patients it reaches its maximum intensity in the first several years.

When eye symptoms or muscle weakness suggest someone has MG, an edrophonium challenge test helps confirm the diagnosis. Other tests of nerve function as well as blood tests for the specific autoimmune antibody contribute to the diagnosis. Doctors also might look for thymus hyperplasia or a tumor; in about three-fourths of MG cases, removing the thymus improves a patient’s health.

Despite a variety of options, MG is difficult to treat. A patient typically requires several types of treatment, each with its own range of side effects. One oral drug works like edrophonium but has less effect over time. Corticosteroids can reduce the autoimmune response. Surgical removal of the thymus results in some improvement for many patients. 

A patient in a myasthenic crisis might receive plasmapheresis in an effort to remove the autoimmune antibodies, though effects only last a few weeks. In the event of such a crisis (in which the respiratory muscles become affected and the patient can’t breathe; this occurs in about 10 percent of MG patients), ventilator support is needed. 

Additional information is available from the Myasthenia Gravis Foundation of America, (800) 541-5454, www.myasthenia.org.