ACUTE MOTOR AXONAL NEUROPATHY

Acute Motor Axonal Neuropathy (AMAN) is a distinctive form of peripheral nerve disorders, which is identified on the base of pathological and electrodiagnostical studies being consistent with pure motor axonal degeneration. Although many causations, including some preceding infections, metabolic diseases, chemical toxins etc, could cause the form, it has been recognized as the one of the two major subtypes of Guillain-Barré syndrome (GBS), particularly in east Asia (China and Japan) with 40–80% proportion of GBS patients, whereas the another most common subtype of GBS, acute inflammatory demyelinating polyneuropathy (AIDP) characterized by typical demyelination at motor as well sensory nerve fibers, still accounts for about 90% of GBS cases in Western countries.

AMAN of GBS is more likely epidemic in children. The major clinical manifestation is muscle weakness usually progressing over a period of several days or more, at the most 4 weeks. Although most patients eventually recover without or with residual disability, death could be occasionally occurring from respiratory failure. Some patients recover quickly within days, which is presumed resulting from the resolution of functional nerve conduction failure originally due to the pathogenetic antibody combined at the Ranvier nodes. Others, however, could experience slow and poor recovery due to severe or extensive axonal degeneration.

AMAN is often triggered by enteric infection of Campylobacter jejuni (C. jejuni). There are frequently increased titers of antiganglioside antibodies (GM1, GM1b, GD1a and GalNAc-GD1a) in patients' sera. Therefore it has been supposed that C. jejuni probably share homologous epitope to a component of the nerve terminal, and the immune responses due to molecular mimicry between carbohydrate structures in C. jujeni and GM1 or other gangliosides cause nerve axonal degeneration. Several recent experiments confirmed the presumption. AMAN models with flaccid limb paresis and typical pathological features at nerve roots were successfully created in rabbits immunized by GM1 or CJ jejuni lipooligosaccharide (LOS). In contrast with parental strain of C. jejuni, its mutant of galE or neuB1 gene, which involved the synthesis of galactose residues or sialylation of GM1-like structures in LOS, no longer induced anti-GM1 antibody but still high level of anti-LOS IgG in serum of guineas pigs immunized with whole cell suspension. Furthermore the immune damage at their sciatic nerves was also no longer significant comparing the parent strain.

IVIg and plasma exchange have been proven to shorten the progressive course of GBS but some reports mentioned that IVIg is more efficacious than plasma exchange for AMAN. Causative management could be important for some AMAN patients associated with metabolic and toxic factors.