Polyneuropathy associated with monoclonal gammopathy of undetermined significance. A prospective study of the prognostic value of clinical and laboratory abnormalities.

The natural course of polyneuropathy associated with monoclonal gammopathy of undetermined significance (MGUS) is not well known. We therefore studied 32 untreated patients for a period of 5 years. Fifteen patients had an IgM M-protein, 15 an IgG and two an IgA. There was a male predominance, a mean age of onset at the end of the sixth decade and sensory signs were more pronounced than motor deficits. On entry into the study and during the 5 years of follow-up, we quantified the neuropathy in a standard way: totals of motor and sensory scores; vibration perception threshold; tapping tests; quantified Romberg test; electrophysiological parameters. A significant difference in the natural history between the polyneuropathy associated with IgM-MGUS and IgG/IgA-MGUS was found for the motor and sensory sum scores, the vibration perception threshold and the tapping tests. The polyneuropathy in IgM-MGUS is more progressive, with significantly more weakness and sensory signs, indicating that the neuropathies associated with IgM-MGUS and IgG/A-MGUS may be two different entities. A rapid progression of the neuropathy was found in five patients. We found no predictive factors for this severe progression of the neuropathy of these five patients. Of these five, three (two IgM, one IgG) developed a non-Hodgkin lymphoma.