I hadn't heard of it, but googled Cytoxan Myasthenia gravis, and found the following: Your doctor may also prescribe other medications that alter your immune system, such as azathioprine (Imuran), mycophenolate mofetil (CellCept), cyclophosphamide (Cytoxan) or cyclosporine (Sandimmune, Neoral). The site was http://www.cnn.com/HEALTH/library/DS/00375.html
and the info was toward the bottom of the page. Apparently it is fairly common. Good question. Are they planning on prescribing that for you?
Hugs,