Plasma exchange in myasthenia gravis

Abstract

The short and long-term response to single or repeated courses of plasma exchange has been studied in thirty patients with acquired myasthenia gravis. A total of 134 courses have been undertaken, and single individuals have received up to 19 corses over two years. Complications related to circulatory access were minimized by the use of a femoral vein catheter kept in situ for the complete course of exchange. Patients treated with prednisone and azathioprine together tended to respond to exchange better than when either drug was given alone or no treatment was given. In most patients the period of improvement attributable to the exchange itself ranged from a few days to three or four weeks. Overshoot of anti-AChR antibody can be observed after exchange, and for this reason it is probably advisable to undertake exchange in association with immunosuppressive treatment. The optimal short-term clinical response was judged as good in 63% of cases, moderate in 27% and poor or absent in 10%. Patients with chronic severe disease (grade IV) showed, on average, a less satisfactory response than those with acute severe (grade III) or moderately severe (grade IIB) disease. The initial anti-AChR antibody level did not appear to influence the effectiveness of the exchange, and a good response was observed in one patient who had no anti-AChR antibody detectable by the immunoprecipitation assay. In the longer term, 60% of cases have improved sufficiently not to require further exchange. Of those still receiving exchange, 75% have chronic severe disease. Patients treated with combined prednisone and azathioprine who improved sufficiently to manage without exchange required only one-to-two courses.