We report a 49-year-old tetraplegic woman with meningeal carcinomatosis secondary to breast cancer. Serial nerve conduction studies in the extremities revealed that the amplitudes of the sensory nerve action potentials (SNAP) and the compound muscle action potentials (CMAP) decreased rapidly within a few days after her admission. Plasma exchanges were done four times and restored the SNAP amplitudes to normal range. The CMAP amplitudes were also increased, but not to the normal range. These electrophysiologic changes were not associated with clinical improvement. Our patient's tetraplegia may be associated with a combination of two different mechanisms; reversible axonopathy caused by humoral factors that can be removed by plasma exchange, and irreversible radiculopathy due to direct cancer cell invasion.