The efficient management of IgM patients with PN confirmed by neurophysiological tests depends on the type of neuropathy: Demyelinating cases with prolonged distal latency must be tested for anti-myelin-associated glycoprotein antibodies to rule out anti-myelin-associated glycoprotein neuropathy; negative cases with chronic ataxia and ophthalmoplegia must be tested for antiganglioside antibodies to exclude CANOMAD (chronic ataxic neuropathy, ophthalmoplegia, Ig M paraprotein, cold agglutinins, and disialosyl antibodies). This evidence concerns the gene MAG and neuropathy.