Reproducibility of normal facial motor nerve conduction studies and their relevance in the electrophysiological assessment of peripheral facial paralysis

To determine the intra-examiner intertrial reproducibility of normal facial motor nerve conduction studies (FNCS) and their relevance in electrophysiological assessments of peripheral facial paralysis, 52 patients with acute unilateral Bell's palsy were examined on two separate occasions 1 month apart. Three electroneurographic methods were assessed. On the unaffected side of the face, FNCS are reliable when performed by a single examiner over time. Nevertheless, compound muscle action potential (CMAP) baseline-to-peak and peak-to-peak amplitude showed a rather high intertrial variability. Reproducibility of the assessed surface electrode recording procedures was similar. Regarding the affected side, in patients with mild axonotmesis of the facial nerve variations of electroneurographic parameters 1 month apart fell within the range of normal intertrial variability. In patients with severe or moderate axonotmesis, the distal latency and the M wave amplitude variations showed significant intertrial variations. Reproducibility of FNCS appears to be similar to that found in limb motor nerves. Normal variability curtails the sensitivity of FNCS in detecting mild facial nerve axonotmesis, although this technique remains useful in severe cases.