The role of nerve monitoring to predict post-operative recurrent laryngeal nerve function in thyroid and parathyroid surgery

Objectives: To determine the role and efficacy of intra-operative recurrent laryngeal nerve (RLN) stimulation in the prediction of early and permanent postoperative nerve function in thyroid and parathyroid surgery. Study design: A retrospective review of thyroid and parathyroid surgeries was performed with calculation of sensitivity and specificity of the response of intraoperative stimulation for different pathological groups. Methods: Normal EMG response with 0.5 mAmp stimulation was considered a positive stimulation response with post-operative function determined by laryngoscopy. No EMG response at >1-2 mAmps was considered a negative response. Results: The number of nerves at risk analyzed was 909. The overall early and permanent paralysis rates were 3.2% and 1.2% respectively with the highest rate being for Grave's disease cases. The overall sensitivity was 98.4%. The specificity was lower at 62.5% but acceptable in thyroid carcinoma and Grave's disease patients. The majority of nerves with a positive stimulation result and post-operative paralysis on laryngoscopy recovered function in 3 to 12 weeks showing positive stimulation to be a good predictor of eventual recovery. Conclusions: Stimulation of the RLN during thyroid and parathyroid surgery is a useful tool in predicting postoperative RLN function. The sensitivity of stimulation is high showing positive stimulation to be an excellent predictor of normal nerve function. Negative stimulation is more predictive of paralysis in cases of thyroid carcinoma and Grave's disease.