Motor neuron disease and paraproteinemia.

We studied two patients with motor neuron disease and paraproteinemia. One had amyotrophic lateral sclerosis (ALS) and IgG lambda monoclonal gammopathy. The second had slowly progressive muscular atrophy and an IgM kappa paraprotein, followed by a biclonal gammopathy when an IgA kappa paraprotein appeared. Treatment with immunosuppressive agents and plasmapheresis lowered the serum concentration of the paraproteins. The ALS syndrome progressed despite therapy. The other patient improved, was stable for several years, but then deteriorated despite continued therapy.