Polyneuropathy in nonmalignant IgM plasma cell dyscrasia: A Morphological study

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Abstract
Six patients had peripheral neuropathy and nonmalignant IgM plasma cell dyscrasia. In 2 of them, immunological studies indicated that the monoclonal Ig reacted with myelin-associated glycoprotein, a constituent of peripheral nerve myelin. Sural nerve biopsy specimens from both patients showed morphological signs of primary damage to the myelin sheath. In the other 4 patients, 2 of whom had a monoclonal IgM.kappa. reactive with chondroitin sulfate C, the axon rather than the myelin sheath was considered the chief site of nerve injury. The morphological findings suggest that the pathogenesis of peripheral neuropathies in IgM plasma cell dyscrasia is heterogeneous. The observations are consistent with a pathogenic interaction of the IgM paraprotein with autoantigens in peripheral nerve in some instances.