VOCAL CORD PARALYSIS (VCP)
Vocal cord paralysis and paresis results from abnormal function of the nerves that control laryngeal muscles. People have two vocal cords, also known as vocal folds, that work together to produce sound. They open during breath to let the air flow into lungs, and they close and vibrate during speech (this is called phonation). To produce good voice, both vocal cords should move toward each other and close completely to vibrate together (this is called glottic closure). Vocal cords move through the contraction of various muscles controlled by the brain and a specific set of nerves. Paralysis is a complete absence of vocal cord movement, caused by a complete loss of nerve input; paresis is a weakened vocal cord movement, caused by a partial loss of nerve input. There are two nerves that can be involved: Vagus nerve is the longest cranial nerve in the body; it exits the brainstem and the skull to enter the neck. It gives off two nerves that supply larynx: 1. Superior laryngeal nerve (SLN) is given off right after vagus nerve’s exit from the skull. 2. Recurrent laryngeal nerve (RLN).
RLN carries signals to different laryngeal muscles responsible for opening, closing, and adjusting tension in the vocal cords. It also carries signals to lower pharyngeal muscle and upper esophageal muscle; these muscles are important for normal swallowing. Healthy function of this nerve is needed for breathing, speaking, coughing, and swallowing. The left RLN is given off the vagus nerve in the chest and turns back into the neck to reach larynx. It can be damaged or compressed by tumors in the left side of neck or chest, or injured after surgery to the left side of neck or chest. The right RLN is given off vagus nerve at the lower most part of neck, however, it does not enter chest; it turns back from low in the neck to larynx. It can be damaged by tumors in the neck or injured during surgery in the neck. The Vagus nerve can be damaged by tumors or surgery of brain stem, skull base, pharynx, neck and left upper chest.
The superior laryngeal nerve (SLN) carries signals to cricothyroid muscle that controls pitch of voice. This muscle tenses the vocal cords for high notes during singing and screaming and shouting. An injury or damage to the SLN can cause inability to increase pitch when singing or reach higher notes. This nerve also receives sensation from larynx; when paralyzed, there is severe aspiration of both liquids and solids into the airway, causing severe coughing episodes.
Causes of vocal cord paralysis
Idiopathic—An idiopathic vocal cord paralysis means that no specific cause could be found despite diagnostic tests. This happens in up to 50 percent of cases. One theory is that the common cold virus may cause nerve inflammation.
Injury during surgery—Surgery in the neck (thyroid gland, carotid artery, cervical spine) or in the chest (lungs, esophagus, heart, or large blood vessels) may cause RLN or SLN paresis or paralysis.
Tumors of the skull base, neck, and chest—Tumors (both cancerous and non-cancerous) can grow around nerves and squeeze them, resulting in varying degrees of paresis or paralysis.
Viral infections—Inflammation from infections may injure the vagus nerve or its branches to the larynx (RLN and SLN).
Auto-immune diseases—Various auto-immune diseases can cause transient or permanent vocal cord paralysis.
Neurological causes—Strokes and other neurological diseases can cause vocal cord paralysis.
The three most common etiologies of VCP are cancer, surgery and idiopathic. Among cancers, cancer of lung, esophagus and thyroid cause VCP by directly invading recurrent laryngeal nerve. Lung cancer is common in our country because of high tobacco consumption. Thyroid cancers are common in our country because of Chernobyl nuclear accident in 1986. Esophageal cancers are infrequent in our country because of low alcohol consumption; these are very common in western countries because of high alcohol consumption. During thyroidectomy and left thoracic surgery (heart, left lung operations) RLN may be damaged. If no cause could be determined for VCP, it is called idiopathic; these cases are considered to be caused by viral infections; virus infects vagus nerve or its branches to larynx and disturbs its function; 2/3 of the idiopathic paralyses recover spontaneously.
On a patient with VCP, the physician’s duty is to search for disorders possible to cause this paralysis. In order to search for the cause of VCP your doctor will order some blood tests and radiological tests. One has to scan the entire head and neck and thorax between brain stem and arcus aorta when searching for the cause of VFP. Many diagnostic tests may be performed for this purpose; however, I prefer CT or MRI of nasopharynx and CT of thorax for left VCP and CT or MRI of nasopharynx for right VCP.
VCP can be simply classified as unilateral or bilateral. Unilateral VCP means only one vocal cord is paralyzed; however, in bilateral VCP both vocal cords are paralyzed.
In unilateral VCP, paralyzed vocal cord stays immobile a little off the midline of larynx; healthy vocal cord cannot come into contact with the paralyzed one; thus, glottal gap and glottal air escape develops. Voice is hoarse and weak; phonation time is short; cough is also weak. The patient has trouble to make the others around him hear his voice. Because there is a lot of air escape through vocal cords while speaking, he has to breathe after each word he says; that is why he appears breathless while talking. The patient aspirates water and food or may be unable to swallow. Aspiration problem is worse when vagus nerve is paralyzed high in the neck or at the skull base because of involvement of SLN. For treatment, paralyzed vocal fold must be brought closer to the healthy vocal fold to correct hoarseness; this is called medialization.
In bilateral VFP, both vocal folds are paralyzed and stay immobile a little off the midline of larynx; they may be aspirated a little bit towards midline during inspiration due to negative pressure. The gap between vocal folds is usually enough for respiration at rest; however, this gap is insufficient during motion and exertional dyspnea develops. Sound (stridor) is produced during breathing. Voice is monotonous and near normal, but it is not normal. However, patients are usually not unhappy with their voice. The patient aspirates water and food or may be unable to swallow. Aspiration problem is worse when vagus nerve is paralyzed high in the neck or at the skull base because of involvement of SLN. For treatment, to correct dyspnea, one of the vocal folds must be lateralized. The voice gets worse while respiration improves. One must inform the patient about this voice loss before the operation.
Before commencing with irreversible treatment we must wait for 6 to 12 months to expect spontaneous recovery. If there is no recovery after 6 months, we can start with surgical treatment. 3-4 weeks after onset of vocal cord paralysis laryngeal EMG may show the cause, the location of injury and healing potential of RLN. It gives us information about whether paralyzed vocal cord will heal spontaneously or not. Repeated laryngeal EMGs a month apart show healing or degeneration of nerve. Laryngeal EMG is useless after 6 months following onset of paralysis.
Unilateral vocal cord paralysis
Voice therapy is helpful for patients with small gap between vocal cords. The patient performs exercises that help him bring vocal cords together. This helps him to speak more comfortably by decreasing air leak during phonation.
In unilateral VCP, paralyzed vocal fold must be medialized. Medialization can be done by two ways: Endoscopic injection or external surgery.
Injection laryngoplasty: Filling material is injected lateral to paralyzed vocal cord in order to push it medially. This is usually done in the office under topical anesthesia, rarely under general anesthesia. Injection needle pierces neck skin to enter larynx; under endoscopic visualization the needle is directed lateral to paralyzed vocal cord and injection is performed. There are short term (gelfoam, collagen) and long term (fat, Ca-hydroxyl apatite, hyaluronic acid, silicone) injection materials. Fat, obtained from patient’s abdominal wall, is the only autologous material available; the others are synthetic and available as commercial material. Short term materials are known to resorb after 1-3 months. Fat stays in larynx forever, but medialization is lost after about six months. Hyaluronic acid remains in vocal cord for about 6 months, calcium-hydroxyl apatite for 6-9 months. Therefore, all materials are temporary and there is no permanent injection material. Therefore, injection laryngoplasty procedure must be repeated every 6-12 months.
Thyroplasty type 1 (Laryngeal framework surgery or medialization laryngoplasty) is done as external surgery under local anesthesia and sedation. A cartilage window is opened on thyroid cartilage on the side of paralysis; a silicon block, titanium plate or any other material is inserted through this window to medialize paralyzed vocal fold. The surgical result is permanent and voice becomes nearly normal. If there is a large gap between vocal cords or there is level difference between vocal cords, arytenoid adduction or adduction arytenopexy must be added to thyroplasty type 1; otherwise voice result will be suboptimal.
Reinnervation is another external surgery option. Here, a branch of one of the neck nerves is anastomosed to distal end of RLN. This does not create active vocal cord motion, instead it brings paralyzed vocal cord to a more favorable position during phonation, so that it meets contralateral vocal fold during phonation. It increases tension and bulk of paralyzed vocal cord muscle. Clinical improvement is observed within 4-12 months postoperatively.
For children with unilateral VCP, injection laryngoplasty is the most frequently chosen treatment option. It is performed under general anesthesia. Recently, reinnervation has gained more popularity as a treatment choice. For adults with unilateral VCP, thyroplasty is preferred most frequently.
Thyroplasty type 1 window and silicon prosthesis
Bilateral vocal cord paralysis
For bilateral VCP there are many surgical options available; the reason for this is that none of the treatments has given an ideal result. Tracheotomy appears as an ideal treatment because it both solves respiratory problem and preserves voice, however, it is just a temporary treatment option because it is not socially acceptable. Vocal fold lateralization by using suture directed into larynx through external needle is an easy and fast surgical option; however, it is a temporary solution, because suture cuts through vocal cord tissue in a few months and vocal cord comes to midline position again and breathing difficulty reappears. This procedure is an alternative to tracheotomy.
During posterior or transverse cordotomy, we perform a lateral cut to vocal fold using CO2 laser. It is done through mouth without skin incision. It is claimed that posterior cordotomy relieves dyspnea whilst damaging voice less. However, in reality the reverse is true: It relieves dyspnea very little, while worsening voice severely. This surgery must be repeated many times due to recurring airway obstruction. It can be performed unilaterally or bilaterally; however, when it is performed bilaterally, there is total loss of voice.
Today the most successful solution for bilateral VCP is endoscopic partial arytenoidectomy or endoscopic total arytenoidectomy (Thornell’s operation) concomitant with laterofixation of vocal cord with endoscopic suture. It is done through mouth without skin incision. It is performed with the help of CO2 laser. It is a one-hour operation. Tracheotomy is not performed. Dyspnea is relieved permanently and voice loss is less. I prefer partial arytenoidectomy as an initial operation; if revision surgery is required I perform total arytenoidectomy.
Before and after left total arytenoidectomy
Reinnervation can be done using a root of nerve to the diaphragm on one side; this root is anastomosed to both muscles responsible for opening vocal cords using Y-shaped nerve graft obtained from neck nerves. Tracheotomy is performed before starting the operation. This is the most ideal solution for bilateral VCP; however, it is a one-day surgery requiring 2-3 surgeons in the team and its success rate is not very high.