Bilateral injury to the recurrent laryngeal nerve (RLN) is a feared complication in thyroid surgery. In association with the visual identification of the nerve, intraoperative neuromonitoring (IONM) can assist in the identification and confirmation of the normal function of the RLN and the external branch of the superior laryngeal nerve. Loss of signal can be a source of confusion, and all possibilities must be considered.

A 70-year-old female patient with a large multinodular goiter and suspected papillary carcinoma in the left lobe of the thyroid was proposed for total thyroidectomy. Due to the suspicion of cancer, it was decided to use intraoperative neuromonitoring. For intubation, succinylcholine was used. During surgery, there was never an EMG activity. In the end, residual curarization was evident, taking an hour for spontaneous ventilation.

In the immediate postoperative period, there was no stridor or dysphonia. A cholinesterase deficiency was suspected, which was confirmed by a serum value of 2800 U/L (4900 - 11900 U/L). The patient was discharged home on the second day, free of symptoms.

IONM is based on nerve stimulation, muscle contraction, and EMG recording. Loss of signal may be due to a pacing problem or a registration problem. The absence of EMG activity may be the first manifestation of cholinesterase deficiency. All surgeons who use IONM must be aware of this possibility when there is no signal since the beginning.