Transcutaneous Facial Nerve Frontal Branch Stimulation to Restore Dynamic Elevation of the Paralyzed Eyebrow in Synkinetic Patients.

Abstract

Background: While patients commonly recover motion following facial nerve injury, aberrant neural regeneration can lead to synkinesis and chronic nonflaccid facial palsy (NFFP); many patients fail to recover volitional eyebrow elevation. Objective: To assess if transcutaneous electrical stimulation of injured frontal branches can achieve eyebrow elevation. Methods: We studied healthy volunteers (N = 10) and patients with unilateral NFFP (N = 36). We performed monopolar transcutaneous stimulation of healthy and paralyzed frontal branches with 4-10 mA pulse trains. We measured eyebrow elevation using Emotrics. Differences between stimulated and volitional elevation were assessed using Wilcoxon signed-rank tests. Results: Stimulable patients (N = 32) were capable of a median of 7.2 mm (interquartile range [IQR]: 5.9-10.5 mm) healthy eyebrow and 1.5 mm (IQR: 0.5-3.1 mm) paralyzed eyebrow volitional elevation. Transcutaneous stimulation of the healthy hemiface achieved a median of 8.5 mm (IQR: 6.3-10.5 mm) eyebrow elevation and 7.2 mm (IQR: 5.3-8.2 mm) on the paralyzed side. Maximum stimulated eyebrow elevation required a median current of 9 mA (IQR: 8-10 mA), which patients felt would be tolerable for daily use in a facial pacing prosthesis. Conclusions: Transcutaneous electrical stimulation can consistently elevate healthy and paralyzed eyebrows in most individuals with NFFP, suggesting they may benefit from dynamic reanimation of eyebrow elevation and possibly other facial regions in future facial pacing systems.