Peripheral neuropathies associated with monoclonal gammopathies of undetermined significance.

Monoclonal gammopathies (MGs) or plasma cell dyscrasias (PCDs) are hematologic disorders that may affect peripheral nerves. An MG is a proliferation of a single clone of neoplastic or nonneoplastic plasma that usually secretes a monoclonal protein (M-protein) serum or urine. If a diagnosis of monoclonal gammopathy of undetermined significance (MGUS) is established, a sudden increase in M-protein levels can indicate malignant transformation of a benign PCD. Roughly 50% of MGUS neuropathies are associated with an IgM gammopathy and the remaining 50% with IgG- and IgA-MGUS-associated neuropathies. MGUS is the most common of the PCDs associated with neurologic disorders, which are easily approached clinically by classifying them as IgM or non-IgM types.