Voice modulation,self-perception and motor branch of the superior laryngeal nerve

ObjectivesVocal morbidity resulting from damage to the motor branch of the superior laryngeal nerve (SLN) after endocrine surgery is well known, but diagnosis is often delayed. The present study aimed to quantify these vocal changes acoustically (main objective), and correlate this with the vocal complaints of patients with suspected SLN motor impairment (secondary objective).Material and methodsThirty females patients with suspected injury of the SLN cricothyroid branch (CT−) were compared to 30 patients without postoperative vocal impairment (CT+) and to 30 control subjects. Mean, minimal and maximal fundamental frequencies (F0mean, F0min and F0max) and vocal range were measured on /e/ at high frequency, sirens (glissandi), a reading text, and minimal intonation pairs. Subjective vocal impairment was evaluated on the Voice Handicap Index (VHI).ResultsA lowering of F0mean associated with vocal range reduction by one fifth (in the reading text) seemed to be specific to CT− patients. Production of questions was affected, with differences in melodic curve and attack. Thyroidectomy within 2 months in itself (without suspected SLN cricothyroid branch injury) also affected these parameters, but to a lesser degree. CT− patients reported greater voice impairment than CT+ patients or controls (P = 0.0004).ConclusionAlterations in speech intonation, quantified on minimal pair test, and self-assessed vocal handicap (VHI) are tools that can easily be used in daily practice to screen for SLN motor branch lesion.     

Intraoperative neuromonitoring by vagus nerve stimulation in thyroid surgery: Clinical assessment of recurrent and superior laryngeal nerves

Intraoperative neuromonitoring of the laryngeal nerves during thyroidectomy is a reliable method to assess nerve function. After identification of the cricothyroid ligament, a bipolar electrode is selectively inserted through the ligament into the thyroarytenoid muscle (TAM) and cricothyroid muscle (CTM). Vagus nerve stimulation then allows precise monitoring of the recurrent laryngeal nerve and the external branch of the superior laryngeal nerve (EBSLN) in the TAM and CTM, respectively. A significant muscle response (greater than 100 μV) is 100% predictive of preserved laryngeal mobility, while the absence of a muscle response is 70% predictive of vocal fold paralysis with 100% sensitivity and 98% specificity. A significant thyroarytenoid muscle response is only recorded ipsilateral to the stimulation with a shorter latency on the right side. A concomitant TAM and CTM response to vagus nerve stimulation or EBSLN stimulation is observed in more than 70% of cases.     

Restoring vocal fold movement after transection and immediate suturing of the recurrent laryngeal nerve with local application of basic fibroblast growth factor: an experimental study in the rat

OBJECTIVE: To evaluate the effects of basic fibro-blast growth factor (bFGF) on the recovery of vocal fold movement and the attenuation of laryngeal muscle atrophy after transection of the recurrent laryngeal nerve (RLN). STUDY DESIGN: Quantitative assessment of vocal fold movement using the video cassette recorder (VCR) image-analysis method and histologic examination of the laryngeal muscle. METHODS: Fifty-eight Wistar rats underwent RLN transection and one of the following three procedures: 1) transection of the RLN alone (transection group, n = 18), 2) suture of the nerve stumps followed by local administration of phosphate-buffered saline (PBS) solution using an osmotic pump (PBS group, n =20), or 3) suture of the nerve stumps followed by local administration of bFGF (FGF group, n = 20). Vocal fold movements were recorded with VCR by way of a rigid endoscope, and the VCR images were analyzed on a computer. Histologic changes in the thyroarytenoid (TA) muscle were evaluated by measuring the cross-sectional area of the muscle and average size of muscle fibers. RESULTS: In the transection group, vocal fold movement did not recover, and atrophy of the TA muscle gradually progressed after sectioning the nerve. In contrast, vocal fold movement as assessed by VCR image-analysis recovered in some cases in the immediate suturing groups, more markedly in the FGF group (34.1 +/- 29.1%) than in the PBS group (5.5 +/- 7.9%) (P <.05). Histologically, atrophy of the laryngeal muscle was significantly attenuated by the local administration of bFGF. CONCLUSION: bFGF facilitates regeneration of the transected RLN and attenuation of intrinsic laryngeal muscle atrophy, thereby restoring laryngeal function.