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Priya et al. J Cancer Metastasis Treat 2021;7:70 https://dx.doi.org/10.20517/2394-4722.2021.122 Page 11 of 17

LOS is defined as either complete loss of amplitude or decrease of the nerve amplitude to 100 µV after
[31]
suprathreshold stimulation (1-2 mA), paying careful attention to troubleshooting algorithms .
Not all cases with LOS will have permanent RLN palsy. The literature suggests that recovery of amplitude to
[40]
50% of baseline amplitude always indicated normal early postoperative vocal fold function . However, LOS
is a grave finding, and, in this series, only 17% of those with LOS intraoperatively exhibited recovery . LOS
[17]
developing acutely was more likely to develop into nerve palsy as opposed to a gradually occurring LOS .
[42]
LOS, if transient, generally recovers within 20 min of occurrence [18,21] .

MANAGEMENT DECISIONS AFTER TRUE LOS
True LOS could suggest either Type I (segmental Injury) or Type II (global Injury).

Segmental injury
There is a positive EMG signal at laryngeal entry point but negative signal at the most proximal point of the
exposed RLN . The point of injury can be picked on stimulating the nerve in its entirety from the distal
[43]
most point of entry proximally. The point at which the signal stops is the point of injury.

Global injury
When there is no EMG signal in the entirety of the visible portion of the nerve, it is Type II injury.
However, the signal is elicited on the opposite vagal stimulation. Figure 6 gives an algorithm on the
management decision in case of true LOS.

OUTCOMES OF USE OF IONM
Performance of the IONM
Various series have reported a high negative predictive value (NPV) of the IONM upwards of 95% [46-48] ,
making it suitable to predict that the nerve is intact. Nonetheless, IONM has a learning curve, and the
operating team may encounter hurdles until a normal signal is achieved. This gives a high false LOS
reducing the positive predictive value of 12%-88%. There has been a prospective randomized controlled trial
comparing conventional thyroidectomy with IONM vs. no IONM. Forty-one nerves at risk in patients with
benign as well as malignant disease were operated on by two experienced surgeons. The findings
demonstrate no RLN injuries in both arms, although the operative time for nerve identification was
significantly lower in the IONM group notwithstanding the fact that total surgery time was not significantly
different. Even in experienced hands, there was one false LOS (1/41, 2.4%) .
[49]

Thus, from available evidence, IONM can prove beyond doubt that the nerve is normally functioning in the
presence of a normal signal and one can proceed with surgery on the contralateral side. However, decision
making in the case of LOS requires expert opinion in high-volume centers to negate false LOS.

Outcomes in surgeries of thyroid cancer
There is growing consensus among thyroid surgeons over deferring contralateral surgery in the event of
LOS on ipsilateral side with the International Neuromonitoring Study Group endorsing this viewpoint .
[20]
While this would be easier in surgery of benign disease, deferring surgery of the contralateral side in thyroid
cancers is a contentious issue and much debated. Needless to mention, apart from a second surgical insult,
there is a question of oncological safety. There is some evidence of favorable outcomes from high-volume
centers, albeit with limited numbers in support of staged surgery. The authors of one study suggested no
deterioration in oncologic outcomes by deferring contralateral surgery in 35 patients of locally advanced
thyroid cancers, both differentiated and medullary cancers [33,50] .