Chronic long-interval plasma exchange in myasthenia gravis

R. L. Rodnitzky and E. P. Bosch

Plasma exchange, when used in conjunction with azathioprine to treat chronic symptoms of myasthenia gravis, can usually be discontinued after a limited period of time without reappearance of symptoms. Patients who cannot be weaned from the procedure are often treated with more potent immunosuppressants to overcome exchange dependence. In view of the cumulative risks of more intensive daily immunosuppression, continuation of intermittent plasma exchange can be an acceptable alternative provided the interexchange interval (IEI) is relatively long. We describe two exchange-dependent patients in whom plasma exchange has been used for 4 1/2 and five years to control their symptoms. In both patients, who also received azathioprine, the IEI gradually lengthened to nine or 12 weeks over two to three years, without the introduction of new immunosuppressants. These cases illustrate that long-term plasma exchange is feasible and effective in selected exchange-dependent patients with myasthenia gravis.