Vocal Outcomes in Vagus Nerve Stimulation: A Laryngeal Pattern-Based Objective Analysis

Abstract

The aim of our study is to evaluate objective and subjective vocal outcomes in patients undergoing vagus nerve stimulation (VNS) therapy for drug-resistant epilepsy and to assess the vocal outcome in the known laryngeal dysmotility patterns induced by VNS. We enrolled 16 adult patients without cognitive impairment who had undergone VNS implant for drug-resistant epilepsy at least 1 year prior. They were evaluated by flexible fibreoptic laryngeal examination and Voice Handicap Index questionnaire administration; acoustic and perceptual voice analysis was performed both at rest and during VNS activation. All recruited patients were admitted to the study. The VNS implant systematically determined laryngeal motility alterations, which were in turn mirrored by perceptual, subjective, and/or acoustic analysis voice alterations in all patients. Patients with intact vocal fold function at rest performed worse during acoustic voice analysis in terms of jitter during VNS activation and shimmer at rest when compared to other laryngeal patterns (P= 0.027 and P=0.034, respectively, Kruskal-Wallis test). Furthermore, VNS activation determined an overall worsening of the perceptual and acoustically analysed voice quality: the grade of hoarseness, instability and breathiness parameters of the GRBASI (grade, roughness, breathiness, asthenia, strain, instability) scale and the jitter, shimmer and noise-to-harmonic ratio of the acoustic analysis worsened significantly during VNS activation (P=0.001, P=0.021, P=0.012, P < .001, P=00.002, P=0.039, respectively, Wilcoxon test). According to our results, the VNS implant determines a significantly impaired vocal outcome that has a surprisingly mild impact on Voice Handicap Index scores. Such impairment is significantly greater in patients with intact vocal fold function at rest.