[Polyneuropathy associated with monoclonal gammapathy: treatment perspectives]

Since the first report of a high prevalence of monoclonal gammapathy (MG) in patients with peripheral neuropathy (PN), some 25 years ago, a large number of such associations have been described. Neuropathies associated with MG have heterogeneous clinical, neurophysiological, neuropathological, and hematological features. The most pertinent relationship seems to be that between distal acquired demyelinating sensory (DADS) neuropathy associated with IgM MG of unknown significance (MGUS) and the presence of serum autoantibodies reacting with myelin-associated glycoprotein (MAG). Other interesting correlations were recently reported in CANOMAD (chronic ataxic neuropathy with ophthalmoplegia, M-protein and anti-disialosyl antibodies). Patients with demyelinating neuropathy (DNP) associated with MG should be screened for malignant plasma cell dyscrasia. MG is more likely to be responsible for the neuropathy if it consists of IgM, if autoantibodies (mainly directed to MAG) are found in serum or on nerve biopsy, and if the clinical manifestations correspond to chronic distal sensory neuropathy. DNP associated with IgM MGUS sometimes responds to immunotherapy but the potential benefits must be considered in view of possible adverse effects. Rituximab, an anti-CD20 monoclonal antibody, has shown promise in this setting. DNP associated with IgG or IgA MGUS may be indistinguishable from chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), in terms of clinical and electrophysiological features and the treatment response. In the POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes), appropriate treatment can lead to a drastic improvement in the neuropathy. Patients with chronic axonal polyneuropathy associated with IgG MG should be screened for Al amyloidosis. However, most axonal polyneuropathies associated with IgG or IgM MGUS are indistinguishable from chronic idiopathic axonal polyneuropathies.