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A cadaveric human specimen showing the close proximity of the thyroid gland (red arrow), overlying the the larynx (hidden) which houses the vocal cords (hidden), windpipe/trachea (green arrow) and the recurrent laryngeal nerve (blue arrow).
Have you ever given a thought to your voice ?Do you know how is your voice produced?In our throat, there is a structure called the larynx which contains the voice box (medical term = vocal cords). The larynx is more prominent in the males producing the prominent Adam's apple in some thin males, which moves up and down visibly on swallowing. Within this structure is the more delicate structure vital to voice production - the vocal cords.However larynx is just more than for voice production. Other important functions are as follows:1.Protection of the airway or preventing liquids, food and other debris from entering your windpipe (the sensation of sudden cough when you have swallowing incoordination) -the most important function2.Normal breathing function 3.Phonation, ie voice production 4.Allowing effort closure in coughing, lifting heaving things, and straining to open your bowels especially when you have constipation.Voice production is the result of a well-coordinated contraction of various delicate muscles that are supplied by nerves. The voice box has 2 important nerve supplies which supply the muscles to move the vocal cords. These are the superior laryngeal nerve (SLN) and recurrent laryngeal nerve (RLN). RLN is the more important of the two as it supplies all muscle of phonation except one (this is suppied by SLN instead). Depending on the cause, the nerves can be completely paralysed ( a.k.a 'palsy') or partially paralysed/weak (a.k.a 'paresis'). Hence loss of the RLN have serious consequences, more so in professional voice users like singers. What are the effects ?The effects due to loss of RLN are: •Voice changes: Hoarseness. Due to air leakage as a result of incomplete vocal cords closure, effects include a breathy voice, extra effort on speaking, gets out of breath more easily on talking, excessive air pressure required to produce usual conversational voice. Diplophonia (voice that sounds like a gargle) can also occur.•Airway problems: Shortness of breath especially on exertion, and ineffective cough and straining efforts.•Swallowing problems: Difficult swallowing. Choking or coughing when swallowing food, drink, or even saliva, and food sticking in throat. Persistent or chronic entry of fluid or food through the windpipe into the lung can cause lung infection (aspiration pneumonia, a potentially fatal condition if not recognised and treated early and aggressively)
How Is Vocal Fold Paralysis/Paresis Diagnosed?Diagnosis can be made after a detailed history-taking from the patient followed by a neck examination and an endoscopic examination of the vocal cords. In most cases, if the event of a recent neck surgery (eg. thyroid surgery) or cancer of the neck or chest which preceeds the voice change is present, diagnosis of vocal cord palsy is almost certain.What Are the Causes?To understand the cause of the RLN palsy, let us now explain the course of the nerve itself. The RLN courses downward into the the chest cavity (a.k.a 'mediastinum') and curves back (like a U-turn) upwards into the neck until it reaches the voice box/larynx. Because the nerve is relatively long and travels a long distance between the neck and chest, it is more liable to greater risk for injury from multiple causes-infections and tumors of the brain, neck, chest, or voice box. It can also be damaged by complications during surgery in the head, neck, or chest, that directly injure, stretch, or compress the nerve. Consequently, the RLN is involved in the majority of cases of vocal fold paresis/paralysis. Known reasons can include:1.Injury during skull base, neck, and chest surgery: Surgery in the neck (thyroid gland, other neck organs carotid artery) or in the chest (lungs, esophagus, heart, or large blood vessels) may inadvertently result in RLN paresis or paralysis. The SLN may also be injured during neck surgery. Bloody surgical fields in some neck surgeries can make identification difficult. Some cancers would have grown so close to the nerve or already infiltrating the nerve, hence sacrificing the nerve is inevitable to have surgical margins free of cancerInjury may be avoided by careful surgical techniques. Nowadays, intraoperative nerve monitoring available for real-time monitoring of the integrity status of the RLN, may reduce the risk of RLN palsy. 2.Tumors of the skull base, neck, and chest : Tumors (both cancerous and non-cancerous) can grow around nerves and squeeze them, causing varying degrees of paresis or paralysis. The main trunk for both the SLN and RLN, vagus nerve can also develop tumours, known as vagal schwanomma (see below), in rare circumstances. Cancers in the skull base, neck, chest can infiltrate into the nerve and render it weak or even paralysed. This tends to be permanent.3.Radiotherapy for head and neck cancers eg like nasopharyngeal cancer (NPC). This can be a delayed complications of radiotherapy following radiotherapy courses given up even up to twelve years later. Once this occur, it tends to be a permanent paralysis and can also affect other cranial nerves causing much functional disruption to the patient. Some would even require a nasogastric tube (a feeding tube that runs through the nose straight into the stomach) to prevent fluid or food from entering the lungs.4.Blunt neck or chest trauma: Any type of penetrating, hard impact on the neck or chest region may injure the nerve(s).5.Viral infections: In some cases, viral infection is deemed to be the cause especially when there is no clear-cut readily-identifiable cause. This is commonly known as 'idiopathic' (unknown origin as there is no confirmatory investigative tests available as well). Normally, inflammation from infections may directly involve and injure the nerves vagus nerve or its nerve branches to the voice box (RLN and SLN). 6.Complication from endotracheal intubation: Compressive injury to the RLN may occur when breathing tubes (intubation) are used for general anesthesia or assisted breathing during a surgery (may not even be head and neck surgery). However, this type of injury is very rare and usually resolves spontaneously.
What Is the Treatment?Treatment depends on a few factors:1.Whether the site of injury is on one side of the neck only or on both sides2.Likelihood of spontaneous recovery which again depends on the underlying cause of paralysis or weakness. The cause of vocal fold paralysis or paresis can indicate whether the disorder will resolve over time or whether it may be permanent. When the cause is thought to be reversible, a watch-and-wait measure can be adopted and temporary/reversible surgical correction can be an option.3.Need for usage of voice in their daily activities. Professional singers would have a higher vocal demand as compared to a computer programmer for example.4.Position of the paralysed vocal cord(s), whether the vocal cord is fixed in an incomplete closure (a.k.a 'adductor palsy') or incomplete opening ('abductor palsy')Generally, treatment can include:•Voice therapy i.e the patient is taught methods to optimise the usage of the voice to improve their voice (think of it like a phystiotherapy for the vocal cords). Voice therapy is normally the first treatment option.•Phonosurgery i.e an operation that repositions and/or reshapes the vocal folds to improve voice function. Usually done under general anaesthesia.In the event the vocal cords cannot close completely leaving a gap thus allowing fluid or food to enter the windpipe or causing air leakage, an implant can be inserted from an external approach over the neck (thyroplasty type I) or materials injected into the voice box (injection laryngoplasty) to 'push' the affected vocal cord to be closer to the opposite normal-functioning cord. This can dramatically improve the voice to a more functional level.
Did you know ?Google CEO says vocal cords affected by "very rare" type of VOCAL CORD PARALYSISRead more here ... (external link)
DR. VINCENT TANConsultant Ear, Nose and Throat, Head and Neck Surgeon,MD (UKM), MS ORL-HNS (UKM), DOHNS RCS Edinburgh (UK), MRCS Edinburgh (UK), Postgrad. Cert.in Allergy (UK), A.M. (Mal), Fellowship in Rhinology (Singapore)Fellowship in Head and Neck Oncology & Surgery (Amsterdam)