A clinical study of motor evoked potentials using a triple stimulation technique

Abstract

Acquired neuromyotonia (Isaac's syndrome) is considered to be an autoimmune disease, and the pathomechanism of nerve hyperexcitability in this syndrome is correlated with anti-voltage-gated K⁺ channel (VGKC) antibodies. The patch-clamp technique was used to investigate the effects of immunoglobulins from acquired neuromyotonia patients on VGKCs and voltage-gated Na⁺ channels in a human neuroblastoma cell line (NB-1). K⁺ currents were suppressed in cells that had been co-cultured with acquired neuromyotonia patients' immunoglobulin for 3 days but not for 1 day. The activation and inactivation kinetics of the outward K⁺ currents were not altered by these immunoglobulins, nor did the immunoglobulins significantly affect the Na⁺ currents. Myokymia or myokymic discharges, with peripheral nerve hyperexcitability, also occur in various neurological disorders such as Guillain–Barré syndrome and idiopathic generalized myokymia without pseudomyotonia. Immuno-globulins from patients with these diseases suppressed K⁺ but not Na⁺ currents. In addition, in hKv 1.1- and 1.6-transfected CHO (Chinese hamster ovary)-K1 cells, the expressed VGKCs were suppressed by sera from acquired neuromyotonia patients without a change in gating kinetics. Our findings indicate that nerve hyperexcitability is mainly associated with the suppression of voltage-gated K⁺ currents with no change in gating kinetics, and that this suppression occurs not only in acquired neuromyotonia but also in Guillain–Barré syndrome and idiopathic generalized myokymia without pseudomyotonia.