Facial nerve excitability after experimental compression.

Animal experiments were designed to test the authors' clinical impression that the facial nerve is frequently hyperexcitable in the very acute stage of intratemporal facial palsy when the damage of the nerve remained neuropraxia. Evoked myograms of the orbicularis oris muscle were recorded before and after clamping of the intratemporal facial nerve of 17 guinea pigs under predetermined constant conditions. In 6 guinea pigs, the evoked responses of the clamped side far exceeded those of the unclamped side. In these animals, electronmicroscopic study revealed that the damage was limited to the myelin sheath.