[Case of pure motor Guillain-Barré syndrome with motor conduction block and anti-GM1/GalNAc-GD1a antibody].

A 38-year-old man presented with distal-dominant limb weakness two weeks after an upper respiratory infection. He had no sensory and autonomic signs and no cranial nerve involvement during the course of the disease. Tendon reflexes were preserved except for an absent Achilles' tendon reflex. His disability at nadir was grade 2 on the Hughes functional scale. Cerebrospinal fluid analysis showed albuminocytologic dissociation and he was diagnosed with pure motor Guillain-Barré syndrome (GBS). Thin-layer chromatography immunostaining and an enzyme-linked immunosorbent assay revealed an immunoglobulin G antibody to the ganglioside complex GM1/GalNAc-GD1a in his acute phase serum. A serial nerve conduction study revealed conduction block in the median and ulnar nerve trunks and temporal dispersion in the tibial nerve, without an evident remyelination pattern during the course of the disease. A sensory nerve conduction study was normal. According to Hadden's criteria, the electrodiagnostic findings were judged as a primary demyelinating pattern. Weakness and abnormal motor nerve conduction recovered rapidly after intravenous immunoglobulin therapy. In view of the localization of GM1 and GalNAc-GD1a on the axolemma of the motor nerves, the clinical course and electrophysiological features may have resulted from functional conduction failure at the nodes of Ranvier of the motor nerves, rather than primary demyelination or axonal degeneration. The illness resembled acute motor conduction block neuropathy characterized by preserved sensory function, an early conduction block at intermediate nerve segments, and good recovery. GM1 and GalNAc-GD1a may form a complex in the axolemma at the nodes of Ranvier or paranodes of the motor nerves, and may be a target antigen in pure motor GBS; especially in the form with acute motor conduction block neuropathy. The present case is the first description of a GBS patient with an IgG anti-GM1/GalNAc-GD1a antibody.