The electrophysiology of thyroid surgery: electrophysiologic and muscular responses with stimulation of the vagus nerve, recurrent laryngeal nerve, and external branch of the superior laryngeal nerve.

Correlation of physiologically important electromyographic (EMG) waveforms with demonstrable muscle activation is important for the reliable interpretation of evoked waveforms during intraoperative neural monitoring (IONM) of the vagus nerve, recurrent laryngeal nerve (RLN), and external branch of the superior laryngeal nerve (EBSLN) in thyroid surgery. Retrospective chart review. Data were reviewed retrospectively for thyroid surgery patients with laryngeal nerve IONM from January to December, 2015. EMG responses to monopolar stimulation of the vagus/RLN and EBSLN were recorded in bilateral vocalis, cricothyroid (CTM), and strap muscles using endotracheal tube-based surface and intramuscular hook electrodes, respectively. Target muscles for vagal/RLN and EBSLN stimulation were the ipsilateral vocalis and CTM, respectively. All other recording channels were nontarget muscles. Fifty surgical sides were identified in 37 subjects. All target muscle mean amplitudes were significantly higher than in nontarget muscles. With vagal/RLN stimulation, target ipsilateral vocalis mean amplitude was 1,095.7 μV (mean difference range = -814.1 to -1,078 μV, P < .0001). For EBSLN stimulation, target ipsilateral CTM mean amplitude was 6,379.3 μV (mean difference range = -6,222.6 to -6,362.3 μV, P < .0001). Target muscle large-amplitude EMG responses correlated with meaningful visual or palpable muscular responses, whereas nontarget EMG responses showed no meaningful muscle activation. Target and nontarget laryngeal muscles are differentiated based on divergence of EMG response directly correlating with presence or absence of visual and palpable muscle activation. Low-amplitude EMG waveforms in nontarget muscles with neural stimulation can be explained by the concept of far-field artifactual waveforms and do not correspond to a true muscular response. The surgeon should be aware of these nonphysiologic waveforms when interpreting and applying IONM during thyroid surgery. 4 Laryngoscope, 127:764-771, 2017.

Liddy W ，Barber SR ，Cinquepalmi M ，Lin BM ，Patricio S ，Kyriazidis N ，Bellotti C ，Kamani D ，Mahamad S ，Dralle H ，Schneider R ，Dionigi G ，Barczynski M ，Wu CW ，Chiang FY ，Randolph G ... -  《-》

Optimal stimulation during monitored thyroid surgery: EMG response characteristics in a porcine model.

To compare electromyography (EMG) characteristics of the external branch of superior laryngeal nerve (EBSLN), recurrent laryngeal nerve (RLN), and vagus nerve (VN) evoked with different stimulation probes/dissectors during monitored thyroid surgery. Experimental porcine model. In five piglets (10 EBSLNs/RLNs/VNs), laryngeal EMG was recorded by endotracheal tube surface electrodes with stimulation using five monopolar probes (group I), three bipolar probes (group II), and two stimulation dissectors (group III). The detectable EMG response (DER) was defined as > 100 μV and was obtained with these different probes/dissectors. Electromyography parameters, stimulus-response curve, and distance-sensitivity results were compared. All stimulation probes/dissectors evoked typical EMG waveforms from the EBSLN/RLN/VN with 1 mA current. A stimulus-response curve with increasing EMG amplitude with increase in stimulating current was noted, with the maximum EMG elicited by group I/III probes/dissectors at < 1 mA and at a higher current for group II probes. All groups recorded lower evoked EMG amplitudes when the nerve was stimulated with overlying fascia or when probe/dissector to nerve distance was greater. The mean amplitude decreased by 11%/33%/13% in group I/II/III probes/dissectors when stimulating nerves covered by fascia versus nerves dissected free of overlying fascia. The rate of obtaining DER at 1- or 2-mm distance was significantly higher in group I than in group II/III probes/dissectors (P < 0.001). Latency did not change with any of the stimulation probes/dissectors or trials. Monopolar, bipolar probes, and newer stimulation dissectors all provided valid evoked VN/RLN/EBSLN waveforms. They have different functional sensitivity profiles and vary when stimulating with fascia and at a distance from the nerve. Selection of a stimulation probe/dissector for nerve monitoring can be based on the stimulation characteristics, the intended nerve monitoring application, and the surgeon's preference. N/A. Laryngoscope, 127:998-1005, 2017.

Wu CW ，Liu X ，Barczyński M ，Kim HY ，Dionigi G ，Sun H ，Chiang FY ，Kamani D ，Randolph GW ... -  《-》

Monitoring of the posterior cricoarytenoid muscle represents another option for neural monitoring during thyroid surgery: Normative vagal and recurrent laryngeal nerve posterior cricoarytenoid muscle electromyographic data.

Intraoperative neural monitoring (IONM) of laryngeal nerves using electromyography (EMG) is routinely performed using endotracheal tube surface electrodes adjacent to the vocalis muscles. Other laryngeal muscles such as the posterior cricoarytenoid muscle (PCA) are indirectly monitored. The PCA may be directly and reliably monitored through an electrode placed in the postcricoid region. Herein, we describe the method and normative data for IONM using PCA EMG. Retrospective review. Data were reviewed retrospectively for thyroid and parathyroid surgery patients with IONM of laryngeal nerves from January to August 2016. Recordings of vocalis and PCA EMG amplitudes and latencies with stimulation of laryngeal nerves were obtained using endotracheal (ET) tube-based and postcricoid surface electrodes. Data comprised EMG responses in vocalis and PCA recording channels with stimulation of the vagus, recurrent laryngeal nerve (RLN), and external branch of the superior laryngeal nerve from 20 subjects (11 left, 9 right), as well as PCA EMG threshold data with RLN stimulation from 17 subjects. Mean EMG amplitude was 725.69 ± 108.58 microvolts (µV) for the ipsilateral vocalis and 329.44 ± 34.12 µV for the PCA with vagal stimulation, and 1,059.75 ± 140.40 µV for the ipsilateral vocalis and 563.88 ± 116.08 µV for the PCA with RLN stimulation. There were no statistically significant differences in mean latency. For threshold cutoffs of the PCA with RLN stimulation, mean minimum and maximum threshold intensities were 0.37 milliamperes (mA) and 0.84 mA, respectively. This study shows robust and reliable PCA EMG waveforms with direct nerve stimulation. Further studies will evaluate feasibility and application of the PCA electrode as a complementary quantitative tool in IONM. 4. Laryngoscope, 128:283-289, 2018.

Liddy W ，Barber SR ，Lin BM ，Kamani D ，Kyriazidis N ，Lawson B ，Randolph GW ... -  《-》

Intraoperative cricothyroid muscle electromyography may contribute to the monitorization of the external branch of the superior laryngeal nerve during thyroidectomy.

Aygun N ，Unlu MT ，Kostek M ，Caliskan O ，Isgor A ，Uludag M ... -  《Frontiers in Endocrinology》

Superior laryngeal nerve quantitative intraoperative monitoring is possible in all thyroid surgeries.

To report normative electromyography (EMG) data on the external branch of the superior laryngeal nerve (EBSLN) and to compare this to analogous data of the recurrent laryngeal nerve (RLN) and vagus nerve (VN) during intraoperative neural monitoring (IONM) using both the standard monopolar stimulator probe and a novel bipolar stimulator probe. Prospective multiple tertiary care center study. A prospective study of EBSLN, RLN and VN EMG data in 22 thyroid surgeries was performed. Subjects with preoperative vocal fold paralysis were excluded. Postoperative laryngoscopy was normal in all subjects. Normative EMG data were acquired using both a standard monopolar and a novel bipolar stimulator probe, as well as a novel endotracheal tube. Cricothyroid muscle (CTM) twitch response during EBSLN stimulation was analyzed. In 100% of cases, EBSLN was identified and quantifiable EMG response was observed. EMG amplitude did not change despite extensive nerve dissection and multiple nerve stimulations. EBSLN amplitude was similar for left and right sides for patients under age 50 and aged 50 or older, for both genders, and with monopolar and bipolar stimulators. Intraoperative neural monitoring may be used to safely assist in EBSLN identification during thyroid surgery in 100% of patients. A novel endotracheal tube allows for quantifiable EBSLN EMG activity in 100% of cases. Monopolar and bipolar stimulator probes produce similar EMG data. 4.

Darr EA ，Tufano RP ，Ozdemir S ，Kamani D ，Hurwitz S ，Randolph G ... -  《-》