Severe motor-dominant neuropathy with IgM M-protein binding to the NeuAcalpha2-3Galbeta- moiety.

We report the occurrence of a relapsing, severe predominantly motor neuropathy in a 75-year-old man with an IGM-K M-protein binding to gangliosides GM2, GM3, GM4, GD1a, GT1b and LM1. Motor nerve conduction velocities were slowed with conduction block. A superficial peroneal nerve biopsy specimen revealed segmental demyelination and remyelination. The patient improved after repeated plasma exchanges, and the antibody titer decreased in association with clinical recovery. This IgM M-protein has a unique, previously unreported binding specificity for terminal NeuAcalpha2-3Galbeta- moiety in common to all gangliosides bound by the antibody except GM2. M-proteins with this affinity may be involved in the pathogenesis of this and other cases of motor-dominant demyelinating neuropathy.