Discontinuous nerve stimulation during thyroidectomy is an alternative to dissection for the intraoperative identification of laryngeal nerves and the prediction of their postoperative integrity.
The thyroid, located at the front of the neck, is responsible for regulating metabolic activities and supporting various other functions such as heart rate and blood flow. Surgical removal of part or all of the thyroid (thyroidectomy) is required to treat a number of conditions, including thyroid tumours (both malignant and benign), hyperthyroidism, hypothyroidism and thyroid nodules.
Damage of the nerves attached to the larynx during thyroid surgery, in particular the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN), is the most significant complication of thyroidectomy.
Unilateral damage of the laryngeal nerves may result in temporary or permanent verbal hoarseness (dysphonia), or difficulty speaking (including trouble producing higher vocal frequencies and projection of the voice) or swallowing (dysphagia). Bilateral damage of these nerves is a more urgent situation as it may lead to difficulty breathing and permanent vocal damage.
Although laryngeal nerve damage during the first thyroidectomy is relatively uncommon (1% to 2%), the likelihood increases significantly with subsequent thyroid surgery (12.5%). The incidence of permanent and transient dysphonia and dysphagia after thyroidectomy ranges from 3.4% to 7.2% and 0.2% to 0.9%, respectively. Thus, it is imperative that surgeons take measures to avoid damaging the laryngeal nerves.
Current practice uses anatomical dissection to identify and preserve the RLN during thyroid surgery, but nerve stimulation has been suggested as a more effective alternative. The surgeon then determines nerve function by inserting a finger into the postcricoid region of the larynx to feel for contraction of the posterior crioartenoid (PCA) muscle in response to RLN stimulation. In a similar fashion, the integrity of the EBLSN can be determined by stimulating the nerve and eliciting a cricothyroid muscle twitch.
Many researches and studies has been undertaken in order to determine the efficiency of nerve stimulation in thyroidectomy and compare the results with thyroid surgery which uses anatomical dissection.
Evidences and results from studies suggest that intraoperative RLN stimulation for locating and predicting vocal cord injuries after thyroid surgery is safe and efficient. Nerve stimulation appeared to offer a level of diagnostic evidence in detecting and conserving the integrity of vocal cord nerves.
Clinical studies on the use of nerve stimulation in thyroid surgery have been done for years in Europe, America, Australia, China and Japan. Since 2008, in Iran, Dr. Ahmed Fanaei, surgeon and specialist in thyroid and parathyroid diseases, apply this approach in his thyroid surgeries.
Leopardi D, “Nerve Stimulation in Thyroid Surgery”, Horizon Scanning prioritizing summary, Department of Health and Ageing, Royal Australasian College of Surgeons, 2008.