Is intraoperative neuromonitoring (IONM) necessary for safe thyroidectomy?
One of the major potential complications of thyroid surgery is damage to the nerves supplying the voice box (the recurrent laryngeal nerves) which run on both sides directly behind the thyroid gland. They may get stretched or damaged during surgery and not work properly after the operation (a nerve palsy). Loss of a single nerve on one side only leads to a croaky voice, whereas loss of both nerves is much more serious as it affects breathing and may require a tracheostomy (external tube into the windpipe). In experienced hands the risk of permanent damage to one nerve should be less than 1 in 100 (<1% of operations), although the rate of damage has been shown to be higher when the operation is performed by less experienced surgeons. Statistically then, the rate of a permanent bilateral palsy (both nerves) should be less than 1 in 10,000. There has been a lot of interest in neuromonitoring (also know as neural monitoring or nerve monitoring) during thyroid surgery. Neuromonitoring refers to the use of a special nerve stimulating probe to induce a signal in the recurrent laryngeal nerve which can be monitored. Loss of the signal is a warning of potential loss of function of the nerve. The proponents of this procedure claim that its use will reduce the risk of nerve damage and allow a less experienced surgeon to find the nerve and perform the operation safely. A number of so-called “Evidenced-Based Guidelines” have been published stating that the routine use of neuromonitoring during thyroid surgery is necessary, proposing it as a mandatory standard of care. Unfortunately no properly conducted research study has ever demonstrated that routine neuromonitoring reduces the risk of permanent damage to the recurrent nerve. In fact, a recent very large study published in the Journal of the American College of Surgeons (see link below) with 245,527 thyroid procedures demonstrates a higher rate of nerve injury with neuromonitoring than with anatomical visualization. There are also many downsides to routine IONM, including cost, and incorrect test results leading to unnecessary cancellation of operations. The evidence clearly supports the safest way to avoid damage to the recurrent laryngeal nerves is for thyroid surgery to be performed by an experienced thyroid surgeon utilizing anatomical visualization, with neuromonitoring reserved for complex cancer or re-do surgery where the nerve is likely already at risk.