MRI of the brachial plexus in polyneuropathy associated with monoclonal gammopathy

On magnetic resonance (MR) imaging of the brachial plexus increased signal intensity and swelling of the brachial plexus has been found in chronic inflammatory demyelinating polyneuropathy (CIDP). Whether these proximal abnormalities are also present in the distal polyneuropathy associated with monoclonal gammopathy is unknown. Therefore, we performed MR imaging of the brachial plexus in 21 patients with polyneuropathy associated with IgM monoclonal gammopathy (11 IgM with anti-MAG antibodies, 10 IgM without anti-MAG antibodies). For comparison we studied 9 patients with polyneuropathy associated with IgG monoclonal gammopathy and 8 patients with CIDP. Among the 30 patients with monoclonal gammopathy, 24 patients had demyelinating polyneuropathy. Among these 24 patients, there was increased signal intensity of the brachial plexus on the T2-weighted images regardless of whether clinical deficits were generalized or purely distal in location. No association was found with the isotype of the monoclonal gammopathy. Of the 8 patients with CIDP, 5 had brachial plexus abnormalities. None of the 6 patients with axonal polyneuropathy associated with monoclonal gammopathy had such abnormalities. Thus, MR imaging of the brachial plexus shows that the distal demyelinating polyneuropathy associated with monoclonal gammopathy is more generalized than presumed.