Long-term clinical and neurophysiological follow-up of patients with peripheral, neuropathy associated with benign monoclonal gammopathy.

The incidence of hematological malignancy in patients with monoclonal gammopathy of undetermined significance (MGUS) has been assessed as 17% to 25%. To ascertain whether this is true of neuropathy associated with MGUS, a long-term (5-42 years) retrospective clinical and neurophysiological follow-up was conducted in 50 cases (immunoglobulin M [IgM], n = 38; IgG, n = 11; IgA, n = 1). Only three patients developed hematological malignancy. Of 25 survivors with IgM paraproteinemia, 7 had myelin-associated glycoprotein antibodies with typical clinical features. Evoked distal muscle amplitudes were significantly smaller than for the other paraprotein classes. Preferential distal demyelination manifested by relative prolongation of distal motor latency was not apparent in the cases of long duration. Two patients with IgM antidisialosyl antibodies and cold agglutinating activity had a large fiber neuropathy with intermittent oculofacial involvement. Both responded to intravenous immunoglobulin. Findings in the remaining patients were varied. Recognition of IgM subgroups is important both for prognosis and possible response to treatment.