Myasthenia gravis is a term meaning “grave muscle weakness.” It is a chronic autoimmune disorder that affects the skeletal, or voluntary, muscles of the body. The most important symptom of the condition is weakness of the muscles during times of activity and its improvement during times of rest. The most widely used classification as given by the Myasthenia Gravis Foundation of America classifies the condition into five classes with each subsequent class representing increased severity.
Causes and Symptoms of MG
The most common muscles that can be affected are those of eyes and eyelids, and those involved in giving facial expressions, chewing, talking and swallowing. Muscles controlling breathing and those of the neck and limbs may also be affected. In this disorder, the body’s immune system produces autoantibodies against the neurotransmitter acetylcholine receptors at the neuromuscular junction. These antibodies block the receptors and prevent acetylcholine molecules from binding to these receptors thereby preventing nerve signals from passing into the muscles. This prevents contraction of the muscles.
Patients will experience symptoms when the number of active acetylcholine receptors decreases to around 30%. It should be noted that cardiac muscles are in no way affected because the cholinergic receptors on these muscle cells have a different antigenicity and antibodies are not formed against them. In many cases, the first symptoms may be weakness of the eye muscles. This may lead to ptosis (drooping of one or both eyelids) or diplopia (blurred or double vision). In other cases, it may be difficulty in breathing and slurred speech. Weakness in arms, legs, hands and fingers may also be experienced by some patients.
Diagnosis of MG
Myasthenia gravis most commonly experienced by females above 40 and males above 60 years of age but it can occur at any age. Since weakness is the most common symptom in this condition, diagnosis is commonly delayed by a year or two. The preliminary steps in diagnosis would include a review of the patient’s medical history, physical and neurological examination. A blood test may reveal the presence of autoantibodies. By injecting edrophonium chloride, a physician can see if muscle weakness can be relieved. Other tests like electromyography and computed tomography may also help in confirming the presence of myasthenia gravis.
Treatment of MG
Myasthenia gravis today is not as grave a condition as its name signifies. There are various therapeutic agents to control and relieve muscle weakness. Anticholinesterase agents like neostigmine and pyridostigmine help neuromuscular transmission. Immunosuppressive drugs including prednisone, cyclosporine and azathioprine are also be used. Thymectomy, or surgical removal of the thymus, relieves symptoms in 70% of the cases. Plasmapheresis is also used in some patients to filter out the offending autoantibodies out of circulation. Which treatment is to be given is decided by the physician based upon the patient’s age, severity of condition and other factors. The prognosis of patients with this condition but undergoing treatment is good and they can expect to lead a healthy and normal life.
References:
1. medicinenet.com *"Myasthenia Gravis" (accessed February 1, 2010)
2. emedicine.medscape.com *"Myasthenia Gravis" (accessed February 1, 2010)
Jitendra Rathod - Jitendra holds a Master's Degree in Microbiology. He had been a Lecturer, teaching the subject to undergrads and postgrads for 8 years.
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