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Myasthenia Gravis

Plasma exchange & thymectomy

11/30/2009

Question:

Hi, I have myasthenia gravis since June 2007. thymectomy done on October 2007. I am on cortisone and cellcept. I tried IVIG many time but was not affected on me at all. On October 2009 I was in crisis. The dr. made plasma exchange for me everyday for 5 sessions. The symptoms gone and after 5 days it`s started to appear again. My question: 1- what I know the affect of plasma exchange last long for 4 to 6 weeks. Why in my case just 4 days? 2- when the thymectomy usually will shows its affect? Thanks

Answer:

I have read case reports of severe myasthenia and seen one patient where it has taken longer to respond to pheresis or had shorter periods of absence of symptoms. This was felt to be related to more damage to the neuromuscular junction and delay in its repair, despite the antibodies being removed, because of longer pre-pheresis disease. Changes happen at the neuromusuclar junction when it has had an immune system attack for a prolonged period, so think of it as a wound which still needs time to heal completely. Or it could be that you are in an especially active phase of the disease. In these cases refractory to standard treatment, I have repeated courses of pheresis. My usual is 5 pheresis sessions of 1.5 body volume exchanges every other day. I have repeated it in 2 weeks at the shortest, because there are complications with pheresis, such as low calcium, heart rhythm abnormalities, anemia, and low platelets (predisposes to bleeding). Your treating physician must be comfortable. Plasma exchange does not suppress the antibodies-it removes them. So you still need something to turn down the immune system (aka cortisone and cellcept). You probably need to discuss with your physician whether he/she thinks the level of immunosuppression is high enough. You can take the antibodies out, but if your immune system is just going to make more, you are only treating the problem partway. Remission after thymectomy at 7-10 years is 40-60% (except patients with thymoma who have a lower remission rate). The effect of thymectomy may take years if it will happen.

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Response by:

Robert W Neel, IV, MD Robert W Neel, IV, MD
Assistant Professor of Neurology
College of Medicine
University of Cincinnati