Mitomycin C induces a delayed and prolonged demyelination and conduction block due to Schwann cell destruction

The intraneural injection of 25 micrograms/ml of mitomycin C produced a prolonged conduction block of delayed onset within the injected nerve. No change in electrophysiological parameters was seen for 6 days after injection, but thereafter a marked drop in the compound muscle action potential (CMAP) amplitude from stimulation proximal to the site of injection occurred, with recovery not being complete until day 97. CMAP amplitude from stimulation distal to the injection site remained unchanged. The reason for this prolonged period of conduction block was apparent from histological examination of the nerve. Light and electron microscope studies demonstrated Schwann cell death, clearly evident at day 8 and followed by subsequent macrophage removal of myelin and Schwann cell debris. Remyelination was not seen until day 40. Hence for periods of about 30 days naked axons persisted through the area of injection. Schwann cells associated with unmyelinated fibres were relatively unaffected, suggesting that myelinating Schwann cells were vulnerable to this agent by virtue of the metabolic processes associated with their myelin maintenance and renewal. These findings indicate that mitomycin C injected intraneurally provides an excellent model to study the effects of Schwann cell disease.