Anti-myelin-associated glycoprotein antibodies and endoneurial cryoglobulin deposits responsible for a severe neuropathy

A 73-year-old man was investigated for a peripheral neuropathy which occurr ed in the course of a Waldenstrom's macroglobulinemia. Serum immuno-fixatio n electrophoresis demonstrated two IgM monoclonal gammopathies of the kappa and lambda chain isotypes, and one had the physical characteristics of cry oglobulin. Immunoblot studies on the patient's serum revealed antibodies wh ich reacted with peripheral nervous system proteins of different molecular weights including the myelin-associated glycoprotein (MAG). An immunofluore scence study of a superficial peroneal nerve biopsy revealed not only a bin ding of IgM and kappa light chain on several myelin sheaths but also the pr esence of IgM and kappa light chain deposits in the endoneurium. On electro n microscopic examination, numerous fibres presented a widely spaced myelin and the endoneurial deposits had the ultrastructure of cryoglobulin. This is the first case presenting features of widely spaced myelin related to se rum anti-MAG activity associated with monoclonal cryoglobulin deposits in t he endoneurium.