Chronic motor axonal neuropathy associated with antibodies monospecific for N-acetylgalactosaminyl GD1a.

We report on three patients with chronic motor neuropathy who had elevated titers of immunoglobulin (Ig)G antibodies against N-acetylgalactosaminyl GD1a (GalNAc-GD1a) and normal titers of antibodies against other gangliosides. Presenting with progressive muscular atrophy, fasciculations, and no sensory deficits, the patients had been diagnosed to have motor neuron disease. Electrodiagnostic features were predominantly axonal. Two patients clinically improved after intravenous Ig infusion and cyclophosphamide therapy. Increased titers of IgM antibodies to GalNAc-GD1a were also found in two of 15 patients with multifocal motor neuropathy with conduction block but were associated with concomitant rise of anti-GM1 antibodies. These three cases represent a chronic motor axonal neuropathy in which antibody testing for a minor ganglioside was helpful for instituting therapy.