Quantitative estimation of the recurrent laryngeal nerve irritation by employing spontaneous intraoperative electromyographic monitoring during anterior cervical discectomy and fusion

STUDY DESIGN: Prospective, clinical study. OBJECTIVE: The objective of our study was to evaluate the role of laryngeal intraoperative electromyography (IEMG) in predicting the development of postoperative recurrent laryngeal nerve (RLN) palsy in patients undergoing anterior cervical discectomy and fusion (ACDF). We also attempted to develop a method to quantify the total IEMG irritation of the RLN. SUMMARY OF BACKGROUND DATA: RLN injury has been recognized as the most common ACDF-associated neurologic injury. It has been postulated, that the employment of laryngeal IEMG may identify the operative events leading to RLN injury and subsequent postoperative palsy. METHODS: Laryngeal IEMG monitoring was performed in 298 patients undergoing ACDF. Preexistent baseline EMG activity, amplitude, and duration of IEMG activity were recorded. The total amount of RLN irritation was expressed as an Irritation Score (IS) applying a specially designed mathematical equation incorporating the amplitude, the duration, and the presence of any baseline EMG irritation. The relationship of IEMG activity with parameters such as the number of operative levels, the duration of the procedure, the presence of any previous neck surgeries, and the type of the used retractor was examined. RESULTS: IEMG activity was recorded in 14.4% of our patients. Postoperative RLN injury occurred in 2.3% of our patients. The sensitivity of IEMG was 100%, the specificity 87%, the positive predictive value 16%, and its negative predictive value 97%. The calculated IS ranged between 0.28 and 3.47 (mean IS: 2.09). Significantly increased IEMG activity was found in patients with previous surgical intervention, patients undergoing multilevel procedures, long-lasting procedures, and cases in which self-retained retractors were used. Likewise, significantly increased IS were observed in patients with previous surgeries and in cases where self-retained retractors were used. CONCLUSIONS: Our study indicates that laryngeal IEMG is a high-sensitivity modality that can provide real-time information and can potentially minimize the risk of operative RLN injury.