Plasma exchange in myasthenia gravis: electrophysiological studies.

Electrophysiological recordings of evoked muscle action potentials during repetitive stimulation were performed in four female patients undergoing plasmapheresis for myasthenia gravis. Studies were done immediately before and after each exchange and were repeated daily during a series of exchanges and at intervals thereafter. Electrophysiological improvement was seen but was delayed for at least seven days from the start of plasmapheresis therapy. No sudden and substantial improvements were encountered, though anti-receptor antibody titers dropped precipitously. A reversible neuromuscular blocking effect of anti-receptor antibody could not be demonstrated in these patients.