Chronic demyelinating neuropathy with IgM-producing lymphocytes in peripheral nerve and delayed appearance of "benign" monoclonal gammopathy.

A chronic demyelinating neuropathy with "benign" IgM gammopathy was followed for 6 years in a 63-year-old man. The clinical, biologic, and EMG aspects were similar to those already reported, but a lymphoplasmocytic infiltrate in the nerve connective tissue of this patient has only rarely been observed in benign IgM gammopathy. The paraprotein was not evident in the serum until 5 years after symptoms of the neuropathy started.