Vocal cord paresis or paralysis is one of the main problems in thyroid surgery. There are two sets of nerves near the thyroid gland that help control the voice. These are the recurrent laryngeal nerve and the external branch of the superior laryngeal nerve. Damage to a recurrent laryngeal nerve can cause you “to lose your voice”. The chance that one of the recurrent laryngeal nerves will be permanently damaged is about 1%.
Temporary voice changes, such as mild hoarseness, voice tiring, and weakness are more common and can happen in 5 to 10% of patients. The temporary problem usually occurs because one or more of the nerves are irritated either by moving them out of the way during the operation or because of the inflammation that happens after the surgery. Although the voice usually improves in the first few weeks after surgery, it can last up to 6 months.
If both recurrent laryngeal nerves are damaged, the vocal cords may close and not allow air to pass from the mouth and nose into the lungs. In this case, a tracheostomy tube may need to be placed to allow passage of air into the lungs. This is extremely rare.
If the external branch of the superior laryngeal nerve is injured and not functioning properly, the vocal cord may move normally. However, it may cause a problem in making high-pitched noises or yelling. These changes are slightly more common, but may be so subtle that they are difficult to notice.
If any of these voice changes last for more than 6 months after the operation, they are likely to be permanent. An otolaryngologist/Ear, Nose, & Throat (ENT) doctor or vocal specialist can be very helpful in determining the specific problem and can perform different procedures to reposition the vocal cord to improve voice quality.
Nowadays use of nerve monitors during surgery has become more common and as a result of these surgical devices the risk of damage to vocal cords has been reduced a lot.
References:
http://endocrinediseases.org/thyroid/surgery_complications.shtml
https://www.verywell.com/complications-after-thyroid-surgery-3233261
