Abstract
Background: Most Recurrent Laryngeal Nerve Palsies (RLNP) occurs with visually intact nerves, indicating neurapraxia. However the mechanism of RLNP neurapraxia in intact nerves is not well understood. During thyroid surgery, Recurrent Laryngeal Nerve (RLN) palsy has occasionally been observed immediately following anteromedial rotation of the thyroid lobe (AMRT), upon identification but prior to dissection of the RLN. We postulated that traction placed on RLN during AMRT may lead to neurapraxia. This study aimed to describe these cases, and to measure Electromyographic (EMG) changes in the vocal cord adductors (VCA) with Vagus Nerve (VN) stimulation, before and after AMRT, and to correlate the EMG findings to prediction of RLN palsy. Methods: Firstly, the cases of RLN palsy following AMRT are described. Secondly, in a prospective study, the EMG amplitudes of 138 VCA muscles following VN stimulation were measured using the Intraoperative Nerve Integrity Monitor (IONM) during thyroidectomy in 90 patients. The EMG amplitudes of VCA with VN stimulation were measured before and after AMRT. All data was collected during a 16-month period, between 2012 and 2013. Standard statistical methods were used to analyse the data. Results: A retrospective series of 7 cases is described where EMG activity with VN stimulation was lost following AMRT upon identification but prior to dissection of the RLN. In the prospective study of 90 patients, anteromedial rotation of the thyroid caused a significant increase in EMG amplitude on the right side (p=0.02) but not on the left (p=0.44). Multivariate analysis identified only extralaryngeal branching of the RLN to be associated with the EMG change. Conclusion: The increase in EMG amplitude of the VCA with right VN stimulation is likely to represent hyper excitability of the RLN after AMRT. Further studies are required to explore the underlying mechanism of this finding, and correlate it to the development of nerve palsy.
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