Myasthenia gravis (MG) is an autoimmune condition that causes weakness that worsens with increasing effort or activity and improves with rest. It often presents with droopy eyelids (ptosis), double vision, and trouble with swallowing or talking. Generalized weakness can also occur.
This condition is due to a problem at the neuromuscular junction where one’s own immune system prevents chemical signals from passing from the nerves to the muscles. This results in fluctuating muscle weakness. MG is caused by an autoimmune response, which occurs when the immune system targets a part of our own bodies rather than foreign bacteria or viruses. The immune system creates antibodies against the receptors on the muscles for the chemical acetylcholine, which prevents the signals from activating the muscles. These antibodies can be detected in the blood in about 90% of people who have MG with generalized weakness, and about 50% of people where MG affects only their eye muscles.
Electroneuromyography (EMG) can also help with the diagnosis, showing decreased muscle responses with repetitive stimulation. A special technique called single fiber EMG is a very sensitive test to assess for the presence of myasthenia gravis and is sometimes used to make the diagnosis of MG. It is not clear what triggers the autoimmune response, but it has been associated with tumors of a gland called the thymus in the chest, as well as certain medications. Your doctor may order a CT scan of the chest to find out if you have an enlarged thymus or a thymus tumor (thymoma), and if so, an operation to remove it may lead to better control of MG.
A number of medications have been used for long term control of MG. These often include a steroid (prednisone) or other immune-suppressing medicine like azathioprine (Imuran®), sometimes together with a medication that helps improve chemical communication between the nerves and muscles such as pyridostigmine (Mestinon®). Some patients may require other medications to be infused intravenously to control their condition such as eculizumab (Soliris).
MG can be life-threatening if it causes weakness of the respiratory muscles. You should let your neurologist know if you develop shortness of breath. If symptoms are mild, a pulmonary function test may be helpful to track your breathing. If you suddenly become severely short of breath, you should call 911 to be taken to a hospital, as symptoms can progress rapidly into an acute “myasthenic crisis” which requires admission to the hospital. Sometimes a ventilator is needed to keep you breathing while special treatments are given. These include intravenous immunoglobulin (IVIG) which downregulates the immune response to the MG antibody, or plasma exchange in which the antibodies are removed from the blood in a “blood-washing” dialysis machine, usually every other day for 5 treatments. MG crisis can sometimes occur in the setting of pregnancy, infections or medication changes.
Our myasthenia gravis program offers the latest diagnostic testing and treatments for MG.