The effects of neuromonitorization in thyroidectomies can be safely evaluated with the standardized technique.

To the Editor,

We read the article written by Demiryas et al. [1] with interest, and we would like to offer some observations about the study based on the current literature.

Though the purpose of the study was to determine the effect of intraoperative neuromonitoring (IONM) on thyroid surgery complications, the explanation of the IONM technique given in the Materials and Methods section was very limited. In addition, it would appear that only the recurrent laryngeal nerve (RLN) was stimulated and vagus nerve (VN) stimulation was not performed.

The International Neural Monitoring Study Group published guidelines for RLN monitoring during thyroid surgery in 2011. The standardized technique includes VN stimulation both before thyroid dissection (V1) and after complete thyroidectomy (V2) [2]. V1 is used as a reference to verify the function of the IONM system and allows for subsequent dissection and RLN identification. V2 testing is the most appropriate technique to predict postoperative vocal cord function [2].

This protocol must be applied in order to optimize the prognostic value of IONM [2]. We suggest that because this standardized technique was not used, and because this study includes the data of patients from 2014 to 2016, the results regarding the effects of IONM might be misleading.

Near-total thyroidectomies in which the RLN is partially visualized and total thyroidectomies in which the RLN is totally visualized were included in both groups. These two different techniques may lead to different RLN paralysis results. Complete dissection is greatly superior to simply localized or partial exposure of the nerve [3]. What were the vocal cord paralysis ratios of the near-total and total thyroidectomies?

The preoperative diagnosis and hyperthyroidism ratios for the two groups were not provided. A high-risk thyroidectomy case, such as a substernal goiter, thyroid cancer, or Graves disease, may prolong the operation time. Without evaluating these factors, can the short duration of the operations in Group 1 only be attributed to IONM?

The total hypocalcemia ratios were lower in the IONM group. Surgical factors, such as the extent of surgery, central node dissection, reoperation for bleeding, presence of Graves disease or thyroid cancer, operation for recurrent goiter, inadvertent parathyroid excision, and parathyroid autotransplantation may also affect the postoperative ratios of hypocalcemia [4]. Can a reduction in the rate of hypocalcemia be attributed to IONM without assessing these considerations?

The conclusion of the article mentions that the authors’ research and similar studies in the literature did not reveal a benefit to IONM usage in terms of decreasing the rate of RLN injury. In the literature, the impact of IONM on RLN paralysis is still controversial. Nonetheless, in a recent meta-analysis of 34 comparative studies on this subject, it was determined that IONM significantly reduced total, temporary, and permanent RLN paralysis [5].

This study [1] is a retrospective study. Features such as the preoperative diagnosis, which can affect the results, were not evaluated and compared. The number of cases was insufficient for a reliable assessment and the standard IONM technique was not implemented. Considering all of these limitations, the conclusions about IONM are questionable.