Anti-SGPG antibody in CIDP: nosological position of IgM anti-MAG/SGPG antibody-associated neuropathy.

Polyneuropathy with monoclonal gammopathy usually is considered a nosological entity different from chronic inflammatory demyelinating polyneuropathy (CIDP). Criteria proposed by the American Academy of Neurology AIDS Task Force (1991), however, show monoclonal gammopathy to be a condition concurrent with CIDP. The purpose of this study was to clarify the nosological relationship between CIDP and IgM anti-myelin-associated glycoprotein (MAG)/sulfated glucuronyl paragloboside (SGPG)-associated polyneuropathy. We investigated IgM anti-MAG/SGPG antibody in 85 CIDP patients by various methods, then examined the relation of M-protein to the presence of IgM anti-MAG/SGPG antibody. In our large study, 17 (20%) of 85 CIDP patients had high IgM anti-SGPG antibody titers in the enzyme-linked immunosorbent assay. This was confirmed by thin-layer chromatography-immunostaining for IgM anti-SGPG antibody and immunoblotting for IgM anti-MAG antibody. Immunoelectrophoresis and immunofixation, respectively, detected IgM M-protein in 6 (35%) and 13 (76%) of the 17 CIDP patients. We conclude that some patients with IgM anti-MAG/SGPG antibody with or without monoclonal gammopathy may be diagnosed as having CIDP, when patients are diagnosed according to the current CIDP criteria.