A causal relationship between
paraproteinemia and neuropathies has been suggested. We studied three patients with chronic sensorimotor
polyneuropathy associated with
plasma cell dyscrasia and
monoclonal gammopathies (IgGK, IgMK,
IgA lambda). Sural nerve biopsies showed mild (2 cases) to moderate loss of myelinated fibers (1 case). Teased single fiber studies showed segmental
demyelination-remyelination in two patients. Direct immunofluorescence demonstrated immune deposits of the myelin sheath of the same specificity as the serum
paraprotein, IgGK (1 of 3 cases). Treatment with
prednisone,
melphalan or
chlorambucil, and
plasmapheresis resulted in remission (1 case), partial improvement (1 case), or had no effect (1 case), although reduction of monoclonal
immunoglobulin occurred in all. To investigate the role the
paraproteins might play in the pathogenesis of the neuropathy, patients' serum was injected intraneurally into rat sciatic nerves. None of the animals developed weakness, slowing of in vitro conduction of sciatic nerve, or significant evidence of
demyelination by light- or electron-microscopy or teased single fiber studies 48 hours postinjection. Similar
injections of rabbit serum with
experimental allergic neuritis (EAN) produced focal segmental
demyelination. Our studies employing an in vivo bioassay technique failed to establish antimyelin activity of monoclonal
immunoglobulin sera.