We reviewed our data from patients with the clinical diagnosis of
chronic inflammatory demyelinating polyradiculoneuropathy (
CIDP). Seventy patients had no demonstrable underlying disease to account for their
polyneuropathy and were classified as idiopathic
CIDP (
CIDP-I). We detected a
monoclonal gammopathy of uncertain significance (MGUS) in 30 patients who were classified as
CIDP-MGUS; 17 had an
IgG gammopathy, 12 an
IgM gammopathy, and one an
IgA gammopathy. Compared with
CIDP-I patients,
CIDP-MGUS patients were older and slightly more likely to be males. When compared with patients with an MGUS but without
polyneuropathy reported in the literature,
CIDP-MGUS patients had similar distributions of age, sex, and
immunoglobulin class. There were no significant differences in motor and sensory nerve conduction measures between
CIDP-I and
CIDP-MGUS patients, nor between
CIDP-MGUS patients with
IgM and those with
IgG or
IgA gammopathy. Strict electrodiagnostic criteria for primary
demyelination were fulfilled by 54% of
CIDP-I patients and 40% of
CIDP-MGUS patients, but these were not significantly different. Our study suggests that (1) the demographic features and
immunoglobulin class distribution of
CIDP-MGUS patients largely reflect those of patients with an MGUS, but without
polyneuropathy, (2)
CIDP-MGUS patients as a group cannot be distinguished from
CIDP-I patients on the basis of nerve conduction studies, and (3)
IgM CIDP-MGUS patients cannot be distinguished from those with other
immunoglobulin classes.