The vocal folds, because of their position in the airway, play a vital role in speech, swallowing and breathing. In order to perform these functions normally, the laryngeal muscles must be able to abduct (open) and adduct (close) the folds. Impairment of these functions may occur on one side (more common) or both sides. These two types of impairment in vocal fold motion differ in their seriousness, symptoms and treatment.
Symptoms: Patients with unilateral paralysis may exhibit a weak and "breathy" voice, and speaking may require considerable effort. Because the vocal folds are unable to close completely during swallowing, patients may also experience coughing and choking while eating or drinking. Patients with bilateral paralysis may experience these symptoms, but the possibility of a blocked airway is a more serious threat. The muscles that normally open the folds and provide for an unrestricted airway are unable to function. Thus, the folds may remain closed in the airway and block normal breathing.
Causes: The most common cause of vocal cord motion impairment is injury to the recurrent laryngeal nerve, the nerve responsible for controlling the muscles of the larynx. This may be the result of trauma, compression during anesthesia, surgery, or other less frequent causes. Occasionally, injury or diseases of the brain, including stroke, may also affect this nerve's function and result in impaired motion.
Mechanical obstruction can also result in vocal fold motion impairment. The arytenoid cartilages, to which the vocal folds attach, can become "locked" and restrict movement. Scar tissue may also accumulate and inhibit vocal fold movement.
Treatment: Two treatment options are available for unilateral motion impairment. In medialization thyroplasty, a surgeon makes a small incision in the skin near the larynx and removes a small piece of thyroid cartilage. A small block, usually made of silicone, is carved, inserted and secured in the cartilage. This block acts as a shim, which pushes the paralyzed vocal fold toward the midline, helping to enhance closure with the other vocal fold. This procedure is relatively quick and painless and is usually performed under local anesthesia.
Recently, preformed implants composed of hydroxylapatite, a substance which closely resembles human bone, have entered U.S. Food and Drug Administration clinical trials. These implants, developed by Dr. Charles Cummings and Dr. Paul Flint, offer more stability and less chance of rejection than those currently in use. In addition, because hydroxylapatite is a bioactive material, these implants can stimulate cartilage growth and help in the repair of the defect. They not bring back motion to the paralyzed cord.
The images below depict the medialization throplasty procedure. The image on the left shows the placement of the shim in the thyroid cartilage. The image on the right demonstrates how this shim, when correctly placed, can help push a motion-impaired vocal fold toward the midline.
The second treatment for unilateral vocal fold motion impairment involves the injection of small amounts of materials directly into the vocal fold. Again, the goal is to push the paralyzed fold medially so the normal cord can close the glottis. This technique, although effective, is limited by the difficulty of controlling the placement and volume of the injected material.
Several different substances are commonly used for injection:
- Autologous fat: Fat has the advantage of being well-tolerated by the body. Because it is taken from the patient, the chances of rejection or infection are small. Additionally, fat provides good vibratory characteristics within the vocal fold. Fat, however, may be resorbed by the body and the procedure may need to be repeated to achieve the desired result long term.
- Gelfoam: Gelfoam is a starch-like material that is quickly absorbed by the body. It is used to provide temporary improvement in patients with laryngeal paralysis. It is particularly useful when the impairment is thought to be temporary or until a definitive procedure can be performed.
- Collagen: Collagen is most often used in the correction of small defects of the vocal fold. It offers good vibratory characteristics, and like hydroxylapatite, it is bioactive. This bioactivity can stimulate fibroblasts to remodel and can result in repair of the defect. Collagen's main limitation is that it is resorbed in an unpredictable fashion.
- Teflon: Teflon lasts longer in the body than fat or gelfoam and is usually used to permanently repair vocal fold defects. When injected, Teflon may cause inflammation, which, if severe enough, can lead to a "stiff" vocal fold that adversely affects voice quality.
Several options exist for the treatment of bilateral vocal fold motion impairment. All of these treatments seek to improve the restriction of breathing that this condition may produce. All procedures try to balance the need for a larger airway with the quality of the voice: The larger the airway, the weaker the voice.
A tracheostomy is a standard and commonly performed procedure in which the larynx is bypassed by opening the trachea and bringing it out to the surface of the neck. A transverse cordotomy is another option and involves removing a small portion of the vocal fold from one or both sides. If breathing is seriously compromised, a cordectomy, or surgical removal of the vocal folds, may be undertaken. Newer procedures for dealing with bilateral vocal fold motion impairment have recently emerged. One of these, a posterior cricoid split, involves splitting the cricoid cartilage and inserting a cartilage graft between the arytenoid cartilages. This allows for a larger opening of the vocal cords posteriorly and can help to relieve the symptom of vocal fold motion impairment. An even newer technique still in the experimental stages, laryngeal pacing, involves implanting a small device that causes coordinated movement of the vocal folds during breathing.