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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 13 of 17

SPECIAL CIRCUMSTANCES
The utility of IONM is being evaluated and appreciated in the following situations.

Mapping of the RLN
In difficult scenarios such as redo surgeries and infiltrative thyroid cancers, the RLN may be difficult to
identify. In such cases, increasing the stimulation intensity to up to 2 mA helps to localize the nerve. After
identification, further stimulation can be done by reducing the intensity to 1 mA .
[39]

Invasive thyroid cancers
The American Head Neck Society, in a consensus statement, has recommended the use of IONM for all
[47]
cases of invasive thyroid cancers . In such cases, with a preoperative mobile vocal cord, if intraoperative
signal at R1 is present proximal to the infiltrative tumor, all attempts should be made at nerve
preservation . Similarly, in the presence of preoperative vocal cord dysfunction, more than 30% patients
[48]
demonstrate an EMG response when stimulated proximally. Preservation of such nerves results in
maintenance of vocalis muscle tone, thus avoiding atrophy and resultant aspiration due to phonatory gap.
Additionally, dissection of the RLN from the tumor while still preserving its integrity has been found to be
easier if IONM is employed.

Day care thyroidectomy
IONM, with its high negative predictive value (> 95%), largely rules out postoperative vocal cord
dysfunction in the presence of normal signal. The confirmation of nerve integrity at the end of the surgical
procedure using IONM can help in making the decision of discharging a patient on the day of surgery
[53]
provided all other criteria are fulfilled .
Paediatric thyroidectomy
In cases of patients less than 18 years with thyroid neoplasms, IONM has been found to be useful;
continuous monitoring is recommended over intermittent monitoring for prevention of complications .
[54]
Technical modifications to the equipment have been made to facilitate the use of IONM in children.

Challenging anatomic variations
Anatomical variations of the RLN are not infrequent, although they cannot be preempted.

(1) Extra laryngeal motor branches of the RLN are not uncommon. The RLN may branch more than 5 mm
away from its entry into the larynx. Failure to recognize such branching may result in palsy despite an intact
appearing nerve . IONM helps in preventing this by identification of the motor branches, especially as
[55]
these smaller branches may be mistaken for branches of the inferior thyroid artery and therefore may be
ligated or cauterized.

(2) Non-RLN: As is well known, a non-recurrent laryngeal nerve is encountered in 0.6%-1% of all
thyroidectomies, and it is almost exclusively seen on the right side . Since there is no cost-effective method
[56]
of identifying it preoperatively, it is best to stay aware of the entity and identify it. IONM is an effective tool
in confirming a non-recurrent nerve if it exists. This is done by confirming an EMG signal from the
laryngeal muscles on proximal stimulation of the vagus nerve at the level of the superior border of the
thyroid cartilage in the absence of such a response distally at the level of the fourth trachea ring.