Measurement of facial nerve conduction velocity and its application to patients with Bell's palsy.

Motor nerve conduction velocity (MCV) of the facial nerve was measured by electrical stimulation of the marginal mandibular branch and by evoked electromyography of the mentalis muscle. Normal MCV was 48.8 +/- 3.68 (mean +/- SD) m/s. In 132 patients with Bell's palsy, the minimum MCV was investigated within 2 weeks after onset. Sixty patients with normal MCV completely recovered in 1 month, but in the other patients with lower MCV, recovery was delayed. All of the 19 patients with markedly decreased MCV (0 to 10 m/s) exhibited partial recovery at 6 months after onset. MCV in Bell's palsy provides a good reflection of the prognosis, and of the degree of nerve damage.