Recording of single fiber electromyography in patients with peripheral facial palsy.

We determined muscle fiber density with single fiber electromyography (SFEMG) to discuss the condition of re-innervation after the recovery of facial movement in cases of peripheral facial palsy. Muscle fiber density was then compared with electroneurography (ENoG) which is thought to correlate with the severity of facial neuropathy in the early stage after the onset. The degree of neuropathy and subsequent recovery of innervation was also discussed. The subjects were 36 patients with peripheral facial palsy (30 patients with Bell's palsy and 6 with Hunt's syndrome), treated at our hospital, in whom ENoG could be recorded within 2 weeks after the onset. Muscle fiber density was determined after the recovery of facial movement. As a control, muscle fiber density was determined in 11 normal adults, and muscles on the healthy side in 23 patients with Bell's palsy. Muscle fiber density was 1.44 +/- 0.15 (mean +/- S.D.) in normal adults and 1.51 +/- 0.18 on the healthy side in patients, showing no significant difference. Data on the affected side were divided into 4 groups according to the minimum ENoG level within 2 weeks after onset and were compared with the normal group. In all cases with an ENoG level of 40% or more, muscle fiber densities were normal, and no significant differences were noted between the affected side and the healthy side. In cases with an ENoG level of less than 40%, muscle fiber density increased significantly with increasing severity of denervation. These findings suggest that collateral sprouting is absent in cases of peripheral facial palsy who show an ENoG level of 40% or more, or no wallerian degeneration.