53. Is the facial nerve injured by a vascular compression in hemifacial spasm? Stimulating single-fiber EMG study

Abstract

Primary hemifacial spasm (HFS) is usually related to a vascular compression of the facial nerve at its root exit zone from the brainstem, and it may result in latent facial nerve injury. Axonal stimulating single-fiber EMG (a-SFEMG) was used to investigate whether facial axons are affected in HFS patients. Facial nerve conduction and a-SFEMG of the orbicularis oculi were performed in 30 patients with HFS and 20 patients with blepharospasm (BS). All the patients had not received prior botulinum toxin treatment. Amplitudes of compound muscle action potentials did not significantly differ between the affected side and non-affected side in HFS patients, and between patients with HFS and those with BS. However, jitter (mean consecutive difference) was significantly greater in the HFS group than in the BS group (p = 0.005). After an initial botulinum toxin injection (10 IU) in the O. oculi, 20% of the HFS patients and 5% of the BS patients presented lagophthalmos. These results suggest that HFS is associated with mild facial nerve injury, and this can lead to vulnerability to botulinum injection.