Characterizing neuropathies associated with monoclonal gammopathy of undetermined significance (MGUS): a framework consistent with classifying injuries according to fiber size.

Neuropathies associated with monoclonal gammopathy of undetermined significance (MGUS) occur frequently in the elderly. Data from 42 consecutive elderly patients with a MGUS-associated neuropathy - 12 patients with IgM MGUS, 25 patients with IgG MGUS, 5 patients with IgA MGUS - were evaluated prospectively using quantifiable clinical criteria and quantitative sensory testing. Results consistent with preferential injury to large fibers were found in patients with IgM isotypes (P <.005) but not in patients with IgG isotypes (P <.0005 to.0004). These findings support an immunologic origin for at least some MGUS-associated neuropathies and provide information important for the clinical evaluation of neuropathies in the elderly.