IONM in Thyroid Surgery: A Portuguese Reality — Is It Time for Routine Use?

Carlos E Costa Almeida
15 de ago.
6 min de leitura

Thyroid surgery is one of the most commonly performed procedures in general surgery departments worldwide. Whether for benign or malignant disease, patients undergoing thyroidectomy are most concerned about the possibility of postoperative voice changes. The overall rate of recurrent laryngeal nerve (RLN) injury following standard thyroidectomy has been reported to range from 2% to 13%, while the rate of permanent injury is approximately 1–2% in experienced hands. The reported incidence is higher when all patients undergo postoperative laryngoscopy and when the RLN is not routinely identified during thyroidectomy.

In this setting, every effort should be made to facilitate the safe identification and preservation of both the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN). In recent years, the use of intraoperative nerve monitoring (IONM) has become increasingly widespread in general surgery departments, helping to make nerve identification and preservation easier, faster, and safer. However, the true value of IONM in reducing nerve injury is still a matter of debate, essentially due to the heterogeneity of studies showing different results. I have to confess that in my daily practice, all patients undergoing thyroidectomy (lobectomy or total) are operated on with IONM. Should we keep this practice?

In 2025, Miguel Allen et al. from Lisbon, Portugal, published a retrospective analysis of all consecutive patients who underwent thyroidectomy (lobectomy or total thyroidectomy) over a 4-year period, with or without IONM. The outcomes analysed included RLN palsy and other complications related to thyroid surgery. Preoperative laryngoscopy was performed to assess vocal cord (VC) function, and postoperative laryngoscopy was performed when clinically indicated (symptoms or LOS). Permanent RLN injury was defined as palsy persisting for more than 12 months.

IONM in thyroid surgery in Portugal. Reducing RLN injuries and singing well after surgery.

This study included 502 patients, corresponding to 719 recurrent laryngeal nerves at risk (RLNAR). Lobectomy was performed in 56.8% of cases, while total thyroidectomy, with or without cervical dissection, was performed in 43.2%. Benign disease was diagnosed in 334 cases, while thyroid cancer was diagnosed in 168 patients. Two patients were excluded from this analysis due to preoperative RLN paralysis.

The authors reported an overall transient RLN palsy rate of 0.56% and a definitive RLN palsy rate of 0.28%. Great! Among the four patients who developed transient postoperative RLN palsy, two had malignant disease (lobectomy and total thyroidectomy with central and lateral dissection), and two had benign disease (completion thyroidectomy and total thyroidectomy). The two cases of definitive RLN palsy occurred in patients with malignant disease, and both underwent lobectomy. The transient RLN palsy rate was 0.29% in the non-IONM group compared with 0.81% in the IONM group (P=0.35). The definitive RLN palsy rate was 0.58% in the non-IONM group, while no definitive RLN palsy occurred in the IONM group (P=0.14). Although these differences were not statistically significant, it is important to note that both definitive RLN palsies occurred in patients operated on without IONM.

Dr. Miguel Allen et al. also reported a progressive increase in the use of IONM over the study period. Overall IONM utilization increased from 35.9% in 2019 to 73.2% in 2022. This progressive adoption may reflect the surgical team’s growing confidence in this technology as their experience increased. The authors also reported that the use of IONM was associated with a significant increase (P<0.05) in operative time for both lobectomy and total thyroidectomy, with or without central compartment dissection.

However, in practical terms, this significant increase amounted to approximately 9 minutes for lobectomy and 24 minutes for total thyroidectomy with or without central compartment dissection. I would argue that this difference is of limited clinical relevance and may simply reflect the time required during the initial learning curve with IONM. Moreover, this finding is not consistent with other published studies reporting no significant difference in operative time with the use of IONM. In the end, I fully agree with Dr. Miguel Allen et al. that this difference in time “might not be clinically significant compared to the potential benefit”.

On the other hand, it would have been interesting to know how much time was required for nerve identification. Did IONM actually reduce the time needed to identify the RLN? Probably so. In difficult cases, IONM may reduce the surgeon’s anxiety and facilitate earlier nerve identification, potentially saving time where it matters most. I think this is a major advantage of IONM and may help explain the increasing use of this technology in clinical practice, as reflected by the progressive adoption reported by the authors.

The first point to highlight from this study is the excellent results reported. The rates of transient and definitive RLN injury were very low compared with those reported in other studies, reflecting an excellent surgical technique. Impressive!

NEMODAY - hands-on course of IONM in thyroid surgery.

A second point I would like to highlight is the systematic use of preoperative laryngoscopy. As the authors state, “recognizing preexisting VC paralysis or hypomobility is essential for accurately interpreting IONM nerve conductivity values.” We must not forget that patients may have preoperative VC paralysis or hypomobility without experiencing any symptoms. In the series presented by the authors, 3.42% of patients had some degree of preoperative VC hypomobility, which was crucial for the correct interpretation of the IONM data. Even in the presence of preoperative VC paralysis, residual intraoperative EMG activity should be preserved to avoid additional postoperative symptoms. So, I fully agree with the systematic preoperative laryngoscopic evaluation of all patients. And remember: it may also be important in the event of litigation.

A third point is the increasing use of IONM over the years. I think this reflects the reality of most surgeons who use nerve monitoring. I personally use IONM in all my cases, and all the surgeons I work with have also increased their use of IONM to 100%.

The authors report a decrease in nerve injuries from 2019 to 2022. However, this observation is not based on a statistical analysis, but rather on the absolute numbers: all permanent RLN injuries occurred in 2019. In my opinion, this is important even in the absence of statistical significance. Why? We are living in a “p-mania” era, where everything seems to be reduced to a P value <0.05. However, as some authors have pointed out, data can have clinical relevance without reaching statistical significance—and the opposite is also true.

For example, if an intervention saves one limb out of 100, it may not reach statistical significance, but its clinical relevance would be enormous. Others may argue that, without statistical significance, such a result could simply be due to chance. And I would answer: OK, that may be true. But can you say that it was not the result of the intervention? Think about this…

A final fourth point I must highlight is the absence of a cost-effectiveness analysis. In my opinion, money must not be introduced in this analysis. Surgeons must base their clinical practice on results and outcomes, not on money. If IONM has advantages for patients, that is the only factor surgeons should consider when advising its use. Guidelines must only use this kind of data for recommendations, not cost issues. Doctors should not give administrations and insurance companies reasons for not buying IONM technology or paying for its use. Always think like the following: If I were going to be submitted to a thyroidectomy, would I want IONM to be used? How much are my voice and my ability to swallow worth? To me, they are priceless.

In conclusion, this is an interesting paper reporting outstanding results in terms of RLN injury from an experienced Portuguese surgical team. I fully agree with the authors when they state that “the results support IONM potential to reduce RLN injury without increasing surgical morbidity.” Keeping in mind that visual identification of the RLN remains the gold standard, and that IONM may assist in this identification, I also agree that “routine use of IONM should be considered to improve patient outcomes, particularly in complex thyroid procedures.”

Finally, I would go one step further and argue that IONM should be considered in all thyroidectomies. Always remember: the easiest thyroidectomy can become the most difficult one in a matter of seconds.