The most feared complication after thyroidectomy is the recurrent laryngeal nerve (RLN) injury. RLN injury causes phonation changes, and swallowing changes (choking). In case of bilateral injury to the RLN, a tracheotomy may become necessary to maintain airway patency. As described in the literature, injury to the RLN occurs in 2-13 % of thyroidectomies, and a permanent injury affects 1-2% of those procedures. It is consensual that visual identification of the RLN reduces the injury rate. Additionally, adding IONM to visual identification reduces transient palsy, has advantages in high-risk thyroidectomies (thyroidectomy for cancer, substernal goiters, big goiters, and reoperations), and reduces RLN palsy in benign disease (including Graves disease). We must not forget that an anatomically normal nerve can be a non-functioning nerve, that is why IONM is so important.
One of the main problems after thyroidectomy is voice changes. Although most are transitory, they reduce the quality of life of patients. The main cause of these post-thyroidectomy phonatory changes is RLN injury. Additionally, injury to the external branch of the superior laryngeal nerve (EBSLN) is associated with high-pitched problems. This means that preserving RLN and EBSLN functions is very important to avoid voice changes. However, doctors must not forget that trauma during endotracheal intubation and laryngotracheal fixation of the strap muscles can also be causes of voice changes. So, the question is: does IONM protect the voice?
Dr. Seung-Kuk Baeka et al from the Department of Otolaryngology–Head and Neck Surgery from Seoul, Republic of Korea, compared two groups of patients submitted to hemithyroidectomy with (A) and without (B) IONM, and two groups of patients submitted to total thyroidectomy with (C) and without (D) IONM. All patients were female and were operated on because of papillary carcinoma.
A voice analysis was conducted before and after surgery. According to the authors, fundamental frequency (F0) – the number of times per second the vocal cord vibrates while making voice sounds – showed a tendency to decrease in all groups. However, a significant decrease was evident in group D compared to group C (p<0.01). The proportion of patients with normal F0 after surgery was significantly lower in patients submitted to total thyroidectomy without IONM.
Changes in F0 gradually increased until 1 month in all groups (with or without IONM), and then showed a tendency to recover. However, changes in F0 were higher in groups B and D (no IONM). After 1 week, changes in F0 were significantly higher in patients submitted to total thyroidectomy without IONM (p=0.04). Additionally, at 1 month the changes in F0 were significantly higher in patients submitted to hemithyroidectomy (p=0.04) and total thyroidectomy (p=0.03) without IONM.
Maximum pitch showed a gradual decrease in groups C and D at 1 week and 1 month. The changes in maximum pitch were significantly smaller (p=0.02) at 1 week in groups A and C (with IONM) compared to groups B and D (without IONM). These changes were higher in total thyroidectomy.
From these results, we can conclude that phonation changes occurred within the first postoperative month, affected more patients submitted to total thyroidectomy, and were more frequent after thyroidectomies without IONM. The differences between hemithyroidectomy and total thyroidectomy were expected and related to the extent of surgery.
The phonation changes reported by the authors point out an EBSLN injury, which is associated with a reduction in F0 and maximum pitch. Since the authors only performed IONM for RLN preservation (did not monitor the EBSLN), and patients with IONM had lower rates of phonation changes, they state that we can decrease the risk of EBSLN injury by performing IONM of the RLN. Why? Terminal branches of the EBSLN communicate with branches of the RLN (human communicating nerve), and the RLN can innervate fibers of the cricothyroid muscle. This also means that reversible damage to the RLN can result in a temporary malfunction of the cricothyroid muscle causing the reported phonation changes. Very interesting and useful to know. Protecting the EBSLN by performing IONM of the RLN is another advantage of using IONM in thyroid surgery, I think.
Based on the presented data, the authors conclude that the “use of IONM during thyroid surgery appears to be an effective method to reduce transient voice alteration after thyroid surgery”. So… Yes, IONM in thyroid surgery can protect your voice.
Although IONM may not have a significant benefit to permanent voice changes, it has a positive impact on quality of life by minimizing voice changes in the early postoperative period after thyroidectomy.
If you have IONM available, why don't you use it?
If you have it, you use it! It is better for you and your patients.
Link to article:
Dr. Carlos Eduardo Costa Almeida
General Surgeon