By Riva Preil
June marks Myasthenia Gravis Awareness Month, the disease that has affected people such as quarterback Brandon Cox, Christopher Robin Milne (son of Winnie the Pooh author A.A. Milne), and Aristotle Onassis. Myasthenia Gravis (MG) is a chronic, non-progressive neuromuscular autoimmune disease characterized by muscle weakness and fatigue. On a cellular level, the physiologic dysfunction occurs at the neuromuscular junction. Normally, the neurotransmitter acetylcholine is released from the axon (nerve ending) where it travels to nicotinic receptors located in the muscle cell membrane. Usually, when the acetylcholine binds to its receptors, muscle fiber contraction occurs. However, in the case of MG, pathologic antibodies circulate in the blood and interfere with the acetylcholine binding. This results in muscle weakness, particularly after periods of increased activity which is alleviated with rest. The muscles most commonly affected are the ocular muscles, the limbs, and possibly even the respiratory system.
Aside from fatigability, the signs and symptoms of MG include ptosis (drooping eyelid due to muscle weakness), strabismus (non-symmetrical alignment of the eyeball), altered facial expression, slurred speech, and impaired chewing, talking and swallowing. MG is often associated with other autoimmune diseases such as hypothyroidism, diabetes mellitus type 1, rheumatoid arthritis, and lupus.
MG can easily be confused with other disorders (slurred speech-stroke, weakness and fatigability- multiple sclerosis, facial muscle weakness- Bell’s Palsy). Therefore, proper diagnosis is important in order to enable proper treatment. Physical examination includes multiple muscle testing, blood test to check for the presence of pathologic antibodies, and EMG (electromyography) to assess the muscle response to repetitive nerve stimulation (which tests muscle fatigability).
The primary treatment for MG is medication. The two types of medications used are acetylcholinesterase inhibitors (ex. neostigmine and pyridostigmine) and immunosuppressive drugs (ex. prednisone and cyclosporine). It may take weeks or even months for medication to take effect. In addition, it is important to bear in mind the decreased endurance, and exercise should be approached with caution and under the guidance of a licensed health care provider familiar with MG. Finally, inspiratory muscle therapy, such as training with an incentive spirometer, diaphragmatic breathing, and pursed lip breathing techniques can help improve respiratory strength, mobility of the chest wall and ribs, and breathing endurance.