Electrophysiologic study of experimental demyelination induced by serum of patients with IgM M proteins and neuropathy

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Abstract
We induced progressive conduction block in feline sciatic nerve by endoneurial injection of serum from 2 patients with demyelinating neuropathy and an anti-myelin-associated glycoprotein (MAG) IgM M protein. The block was long-lasting (up to 4 days) and affected about half the motor nerve fibers. Control serum from patients with an IgM M protein that did not react with MAG produced a transient block (<48 hours) that affected an average of 25% of motor fibers. Nerves with sustained block showed widespread demyelination of many nerve fibers, exceeding controls. The findings support the view that chronic demyelinating neuropathy in these patients is caused by the anti-MAG M protein.