Immunocytochemical studies of human peripheral nerve with serum from patients with polyneuropathy and paraproteinemia.

Immunohistochemical binding of IgM paraproteins to nerve was studied using the immunoperoxidase technique with serum from 10 patients with benign plasma cell dyscrasia and neuropathy. We stained the myelin sheaths of peripheral nerves and roots fo five patients who had myelin-absorbable IgM paraproteins. Two patients with IgM paraproteins that did not react with myelin showed predominant staining of axons, while three were completely negative. Serum specimens from normal volunteers and patients with paraproteinemias or ALS were also unreactive. Immunocytochemical methods can detect IgM paraproteins with an affinity for nerve antigens and may assist in the diagnosis and classification of plasma cell dyscrasia associated neuropathy.