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Saturday, May 25, 2013
Myasthenia Gravis and Anesthesia
I was curious to know the effects of anesthesia on MG patients in remission. I heard that there is a possibility of a relapse.
Patients with myasthenia gravis have a rare disorder of the nerve-muscle junction resulting in muscle weakness. In myasthenia the body produces antibodies to the nerve-muscle junction - this is one of the so-called "auto-immune" diseases.
There is no evidence that I am aware of that anesthesia affects the disease process itself - i.e. that a "relapse," as you put it, occurs. However, a variety of surgical and anesthetic factors do come into play that may aggravate things and make the condition of patients with myasthenia gravis considerably worse.
For example, muscle relaxant drugs are used routinely in anesthesia to make it possible to insert the breathing (endotracheal) tube and to keep the patient still during surgery. In patients with myasthenia, much smaller doses should, and are, used and yet these drugs may still produce residual effects making the patient profoundly weak after the anesthesia and surgery has ended. If the weakness is bad enough, the patient may be unable to breathe properly. One of the most common medications used to treat myasthenia, the "anticholinesterase" agents, may interact with certain muscle relaxants making them more difficult to reverse. Local anesthetic drugs such as lidocaine, and inhaled anesthetics ("gas") also have muscle relaxant properties which may cause weakness in a patient with severe myasthenia. Then there are non-anesthetic medications including certain antibiotics that also affect muscles and thus cause further problems.
Patients undergoing non-emergency surgery should therefore be in the best possible condition beforehand, with their medications reviewed by an expert, and recommendations made for how to adjust them during the period before, during and after surgery. Other conditions that may be associated with the myasthenia, such as thyroid problems, or diabetes, should be attended to. In a patient with a severe form of the disease, plans may need to be made to keep the patient mechanically ventilated (breathing machine) in the ICU for some time after surgery. Special measures such as plasmapheresis, in which the blood is temporarily "cleansed" of antibiotics may be necessary.
Despite the problems and issues I’ve described, it appears that most patients with myasthenia get through their anesthesia without major complications. Muscle relaxants can often be avoided entirely, and short-acting drugs used. If you have myasthenia, be sure to mention it to your surgeon and of course to your anesthesiologist. It is wise to arrange a preoperative consultation with your anesthesiologist when you can be carefully evaluated and appropriate plans made for controlled and safe anesthesia and postoperative care. Be sure to bring records of any previous procedures with you as these are a useful guide for all the doctors.
Gareth S Kantor, MD
Assistant Professor of Anesthesiology
School of Medicine
Case Western Reserve University