Axonal neuropathy associated with monoclonal gammopathy of undetermined significance

Objective-The neuropathy associated with monoclonal gammopathy of undetermined significance (MGUS) is typically a predominantly demyelinating process that may have additional features of axonal degeneration. Sixteen patients with MGUS and a pure or predominantly axonal neuropathy are reported and compared with 20 consecutive patients with demyelinating neuropathy and MGUS who were seen during the same period. Methods-Retrospective review of a consecutive series of patients with neuropathy and MGUS evaluated during a five year period. Results-The axonal group had mild, symmetric, slowly progressive, predominantly sensory neuropathy, usually limited to the legs. There were no differences in the age of onset or duration of symptoms at the time of presentation, initial symptoms, or the severity of weakness between the axonal and demyelinating cases. However, the axonal process was associated with less vibration and proprioceptive loss, did not include leg ataxia (present in 55% of patients with demyelinating type), less often had generalised areflexia (19% v 70%), IgM gammopathy (19% v 80%), and anti-MAG antibodies (0% v 40%), and had lower CSF protein concentrations (mean, 49 v 100 mg/dl). The illness was also generally milder with less disability (mean Rankin score 2.1 v 2.8). Fewer patients with axonal neuropathy improved with immunomodulating therapy (27% v 75%). Conclusion-There is an axonal neuropathy associated with MGUS that is clinically and electrophysiologically distinct from the more typical demyelinating pattern.