The electrodiagnostic findings in polyneuropathies associated with IgM monoclonal gammopathies

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Abstract
Electrodiagnostic studies were analyzed in patients with neuropathy associated with IgM monoclonal proteins, 7 with anti‐myelin associated glycoprotein reactivity (MAG) and 7 nonreactive to MAG. The findings were distinctly different in the two groups. The electrodiagnostic studies of all the MAG‐reactive patients had demyelinating features with slowing of conduction and prolonged distal latencies while only one of the MAG‐nonreactive patients had a demyelinating pattern. In fact, the MAG‐nonreactive patients were a heterogeneous group, both electrodiagnostically and clinically. This study supports the concept that MAG‐reactive polyneuropathy is demyelinating in type, and is caused by the activity of the IgM M‐protein directed at an antigen in the myelin sheath.