Prognostic Indicators of Non-Transection Nerve Injury and Vocal Fold Motion Impairment After Thyroid Surgery – Correlation Between Intraoperative Neuromonitoring Findings and Perioperative Voice Parameters

Abstract

ObjectivesIn patients with recurrent laryngeal nerve (RLN) injury after thyroid surgery, unrecovered vocal fold motion (VFM) and subjective voice impairment cause extreme distress. For surgeons, treating these poor outcomes is extremely challenging. To enable early treatment of VFM impairment, this study evaluated prognostic indicators of non-transection RLN injury and VFM impairment after thyroid surgery and evaluated correlations between intraoperative neuromonitoring (IONM) findings and perioperative voice parameters.Methods82 adult patients had postoperative VFM impairment after thyroidectomy were enrolled. Demographic characteristics, RLN electromyography (EMG), and RLN injury mechanism were compared. Multi-dimensional voice program, voice range profile and Index of voice and swallowing handicap of thyroidectomy (IVST) were administered during I-preoperative; II-immediate, III-short-term and IV-long-term postoperative periods. The patients were divided into R/U Group according to the VFM was recovered/unrecovered 3 months after surgery. The patients in U Group were divided into U1/U2 Group according to total IVST score change was <4 and ≥4 during period-IV.ResultsCompared to R Group (42 patients), U Group (38 patients) had significantly more patients with EMG >90% decrease in the injured RLN (p<0.001) and thermal injury as the RLN injury mechanism (p=0.002). Voice parameter impairments were more severe in U Group compared to R Group. Compared to U1 group (19 patients), U2 Group (19 patients) had a significantly larger proportion of patients with EMG decrease >90% in the injured RLN (p=0.022) and thermal injury as the RLN injury mechanism (p=0.017). A large pitch range decrease in period-II was a prognostic indicator of a moderate/severe long-term postoperative subjective voice impairment.ConclusionThis study is the first to evaluate correlations between IONM findings and voice outcomes in patients with VFM impairment after thyroid surgery. Thyroid surgeons should make every effort to avoid severe type RLN injury (e.g., thermal injury or injury causing EMG decrease >90%), which raises the risk of unrecovered VFM and moderate/severe long-term postoperative subjective voice impairment. Using objective voice parameters (e.g., pitch range) as prognostic indicators not only enables surgeons to earlier identify patients with low voice satisfaction after surgery, and also enable implementation of interventions sufficiently early to maintain quality of life.

Necessity of Routinely Testing the Proximal and Distal Ends of Exposed Recurrent Laryngeal Nerve During Monitored Thyroidectomy

“…From the results of this study, it can be found that permanent VC palsy rarely occurred in nerve injuries caused by traction or dissecting trauma, but there was a high rate of permanent VC palsy (40%, 2/5) in thermal injuries. The voice outcome and VC mobility prognosis are worse in patients with thermal RLN injuries than in those with mechanical RLN injuries ( 30 , 31 ). Therefore, the use of EBDs or electrocauterization near the RLN should pay special attention to the safety distance.…”

Is There Any Reliable Predictor of Functional Recovery Following Post‐thyroidectomy Vocal Fold Paralysis?

“…None of the above studies included [32] or managed to correlate [21] IONM results and FFL findings to predict progression of transient VFP to permanent. While, in an intriguing study by Huang et al [22], IONM findings and perioperative voice parameters were examined to predict voice outcomes and can perhaps be applied on future ENT protocols.…”

“…Predictive factors for permanent VFP differ among studies depending on instruments, such as laryngeal electromyography [19, 20] or laryngostroboscopy [21], and protocols, such as voice indexes [22], implemented. Although the results of such studies have individually identified possible predictive factors, due to the variability of methods applied or their complexity, none has gained general consensus or has been widely applied.…”

Safety Parameters of Quantum Molecular Resonance Devices During Thyroid Surgery: Porcine Model Using Continuous Neuromonitoring

“…High temperatures are unavoidable when using EBDs, and direct or indirect thermal energy can transfer to the recurrent laryngeal nerve (RLN) and result in thermal injury (3)(4)(5). RLN thermal injury causes more irreversible impairment of vocal cord movement than RLN mechanical injury, resulting in more voice disturbance (6,7).…”