Impairment of peripheral nerve excitability

Functional abnormalities, especially the excitability changes of axon in the peripheral nerve involvement, were reviewed. In GBS and CIDP, the correlation between conduction block and anti-ganglioside antibodies have been discussed. Using anti GM1 antibody positive sera, the suppression of voltage-gated sodium channels (VGSC) has been reported. Although this findings have not been confirmed, the involvement of VGSC may be an important mechanism for eliciting conduction block. In Isaacs' syndrome, voltage-gated potassium channels (VGKC) were suppressed by autoantibodies to VGKC. Furthermore, in generalized myokymia syndrome which shows only myokymia and muscle cramp without grip myotonia, VGKCs are also suppressed in some cases. These findings suggest that some patients with myokymia and neuromyotonia are induced by anti-VGKC antibodies. For evaluating the axonal excitability in vivo, the threshold electrotonus method have been developed and applied for the involvement of peripheral nerves. In ALS, impairment of potassium conductance was shown and was speculated to have the possible rrelation with fasciculation. Thus threshold electrotonus method will be an important method for evaluating axonal excitability in human. The accumulated knowledge about the involvement of axonal ion channels will expand and will be categorized as axonal channelopathies.