Waldenström's macroglobulinemia and peripheral neuropathy: deposition of M-component and kappa light chain in the endoneurium.

Some cases of peripheral neuropathy associated with benign IgM monoclonal gammopathy, or Waldenström's macroglobulinemia, are probably of autoimmune origin; in some cases, anti-IgM serum reacts with the myelin sheaths of peripheral nerves. However, mechanisms may differ in other cases. In one case of neuropathy with macroglobulinemia, we found deposits of IgM immunoglobulin in the endoneurium. On ultrastructural examination, the deposits had erased the basement membrane of some nerve fibers that showed damage of both myelin and axon.