Neuropathy associated with immunoglobulin M monoclonal gammopathy: A combined sonographic and nerve conduction study

INTRODUCTION: We assessed the specific sonographic pattern of structural nerve abnormalities in immunoglobulin M (IgM) neuropathy and disease controls. METHODS: We enrolled 106 incident patients—32 patients with IgM neuropathy, 42 treatment‐naive patients with chronic inflammatory demyelinating polyneuropathy, and 32 patients with axonal neuropathies. All patients underwent standardized ancillary testing in addition to standardized sonography of the brachial plexus and the large arm and leg nerves bilaterally. RESULTS: We found widespread nerve enlargement in IgM neuropathy and chronic inflammatory demyelinating polyneuropathy (CIDP), with specific enlargement of brachial plexus and proximal segments of median nerve but not in axonal disease controls (P < .001). Sonographic nerve hypertrophy in IgM neuropathy was not associated with nerve conduction, clinical, or laboratory characteristics. DISCUSSION: Immunoglobulin M neuropathy is characterized by widespread nerve enlargement indistinguishable from CIDP. Our data provide evidence to confirm that the disease process is not confined to the more distal parts of nerves in either classical demyelinating or axonal variants of neuropathy with associated IgM.