Vocal cord paresis
Recurrent laryngeal nerve paralysis (also called vocal fold paralysis) is the medical term describing an injury to one or both recurrent laryngeal nerves (RLNs), which control all muscles of the larynx except for the cricothyroid muscle. The RLN is important for vocalization, breathing and swallowing.
|Vocal fold paresis/paralysis|
|Classification and external resources|
The primary larynx-related functions of the mainly efferent nerve fiber RLN, include the transmission of nerve signals to the muscles responsible for the regulation of Vocal folds position and tension to enable vocalization, but also the transmission of nerve signals from the mucous membrane of the larynx to the brain.
A unilateral injury of the nerve typically results in hoarseness caused by a reduced mobility of one of the vocal folds. It may also cause minor shortages of breath as well as aspiration problems especially concerning liquids. A bilateral injury causes the vocal folds to impair the air flow resulting in breathing problems, stridor and snoring sounds and fast physical exhaustion, strongly depending on the median or paramedian position of the paralysed vocal folds. Hoarseness seldomly appears with bilaterally paralysed vocal folds.
Definition / Classification
Physicians often use the term recurrent laryngeal nerve paralysis to describe a partial or complete immobility of one or both vocal folds. This definition may be misleading from a medical point of view, as scar formation at the larynx after long-term intubation, injuries (luxations) and inflammation of the cricoarytenoid joint (rheumatism) or tumor ingrowth into the vocal fold can prevent motion of the vocal folds. The physician should therefore clarify in further examinations if a recurrent laryngeal nerve paralysis is present. Every (unclear) vocal fold immobilization should be clarified, as other causes, such as cancer, must be addressed differently.
Recurrent laryngeal nerve paralysis is often called vocal fold paralysis/paresis. Exact terminology varies from area to area, but in general a vocal fold paresis describes the weakness of the posterior cricoarytenoid muscle and a certain kind of impairment of the function, while a vocal fold paralysis means a general loss of function of this muscle resulting in a full loss of mobility.
Vocal fold paralysis may either be unilateral or bilateral, central or peripheral. The paralyzed vocal fold may be immobilized in various positions: median, paramedian (most frequent position) or, less often, intermediate or lateral.
Vocal fold paralysis may be flaccid or, in most cases, rigid (i.e. muscle tension is maintained). Many paralyses are initially flaccid and become rigid over time. The reason is believed to be an undirected regrowth of the nerve from the site of the injury to the inner larynx muscles. This usually causes tension but does not lead to mobility of the vocal fold. Such miswiring of nerves is known as synkinesis.
Unilateral (UVFP) and bilateral paralyses (BVFP) are characterized by different main symptoms.
Unilateral recurrent laryngeal nerve paralysis causes hoarseness due to an incomplete closure of the vocal folds during vocalization. This leads to a soft, breathy voice which cannot be raised. An additional problem is shortness of breath when speaking because air escapes unused during the vocalization. Breathing is often only impaired by an unfavorable position of the paralyzed vocal fold because opening of the other, healthy vocal fold at rest or slight exertion is sufficient. If the original nerve, the vagus nerve is affected too, choking and problems with swallowing may additionally occur.
Bilateral recurrent laryngeal nerve paralysis causes at least a severe reduction of the glottis opening - even complete closures in extreme cases. In addition, the flaccid vocal folds are sucked in by the respiratory flow (Bernoulli's principle). The respiratory flow is often severely impaired. Under exertion, when suffering from respiratory tract infections and frequently during sleep this causes dyspnea and audible respiratory sounds when breathing (stridor). Patients often snore very loudly, partly with dangerous apneas (sleep apneas). In extreme cases bilateral paralysis may require treatment with a tracheal cannula. Patients consider this life-saving treatment a social stigmatization which causes additional stress. A reduced air exchange between lung and environment often leads to shortness of breath in patients with bilateral paralysis. With additional diseases like the flu, this can lead to severe dyspnea. Laughing and emotional situations may also cause dyspnea. Patients often suffer from a deteriorated quality of sleep and may have to take naps during the day. The permanent undersupply with air may also cause cardiovascular diseases (e.g. high blood pressure). Muscle pain due to insufficient breathing is observed less often. The physical performance is severely impaired particularly in patients with bilateral recurrent laryngeal nerve paralysis. Patients are often significantly limited in their daily lives. Most patients with bilateral recurrent laryngeal nerve paralysis are long-term or even permanently incapacitated.
Apart from thyroid surgeries, which are the most common reason for vocal fold paralysis in hospitalized patients, also cervical spine surgeries and carotid endarterectomies are mentioned. Other causes for the disease are tumors, idiopathic reasons, trauma, radiation and nerve lesions after viral infections.
Paralysis of the vagus nerve may be caused by stroke, i.e. hemorrhage or vascular obliteration in the brain (i.e. Wallenberg Syndrome). Malign tumors, e.g. thyroid carcinoma, or metastases of malign tumors can damage the recurrent laryngeal nerve or the vagus nerve and lead to paralysis. Brain tumors may damage the area of origin of the vagus nerve. Recurrent laryngeal nerve paralysis is rarely caused by direct injury of the neck or pressure on the nerve, e.g. by a breathing hose. Recurrent laryngeal nerve paralysis may have many causes which cannot always be verified. Such idiopathic paralyses often concern the entire vagus nerve. Unverifiable virus infections of the nerve or reactivation of already present viruses (mainly zoster/chicken pox) are suspected.
|Cause||UVFP in % of total||BVFP in % of total|
|Thyroid surgery (struma surgery)||12-16||27-49|
|CNS / Neuropathy||3-5||7-11|
|Other (radiation, stenosis, ..)||4-7||4-7|
Standards to clarify vocal fold paralysis are not homogenous. Important indications of possible causes are revealed in accurate anamneses.
In the presence of neural lesions with unknown cause, a thorough ENT endoscopy with additional imaging techniques (computed tomography (CT) of the chest, particularly in the case of left-sided paralyses, and magnetic resonance imaging (MRI) of the neck including the base of the skull and the brain, ultrasound examination of the neck) are performed to exclude tumors along the laryngeal nerves.
When tumor formation is suspected, parts of the hypopharynx and the upper esophagus and passive mobility of the arytenoid cartilage are endoscopically examined under anesthesia.
Voice diagnostics are used to assess voice quality and vocal performance. Voice assessment is necessary to plan and estimate the success of a possible speech therapy.
In incompletely or only partially healed paralyses, stroboscopic larynx examinations yield a type of slow motion picture to assess tension and fine mobility of the vocal folds during vocalization. Stroboscopy and voice assessment are important to establish an individual treatment plan to improve the voice.
Electromyography of the larynx muscles (larynx EMG), which measures the electrical activity of the larynx muscles via thin needle electrodes, allows better differentiation between a neural lesion and other causes of impaired mobility of the vocal fold and localization of the lesion along the nerve. The larynx EMG can, within limits, provide a prognosis of the development of a recurrent laryngeal nerve paralysis. Patients with a poor chance of healing can be identified at an early stage. Unfortunately, this advanced examination technique is not available in all treatment centers.
The treating physician must view all examination results combined and establish an individual diagnosis and treatment plan for each patient.
Scientific opinions on this topic assume up to 80.000 unilateral vocal fold paralyses each year in the US, while the more seldom bilateral paralysis is said to be around 10.000 new incidences each year. Detailed information in scientific literature is, however, very limited and not always clear. Scientific assumptions are also available for the German speaking countries. Estimations for that region mention around ten thousand unilateral and nearly one thousand bilateral vocal fold paralyses per year.
Treatment depends on the cause of the paralysis and main medical conditions. If the vocal fold immobility or the recurrent laryngeal nerve paralysis is caused by a disease requiring treatment, e.g. a tumor, suitable therapy should be initiated. If the medical conditions are minor, e.g. in a quickly recovering unilateral paralysis, special treatment is not always necessary. After the diagnosis, the ENT surgeon or laryngologist/speech-language pathologist will perform follow-up examinations.
For unilateral vocal fold paralysis with poor voice, treatment aims at improving vocal performance. The preferred treatment is speech therapy. Special exercises help to improve closure of the vocal folds when speaking. The contact of the two vocal folds should be as complete as possible to allow efficient and harmonic vibration during vocalization. If this goal cannot be reached with speech therapy, further steps are required. Such steps aim at moving the paralyzed vocal fold closer to the center (medialization), i.e. to the healthy side. In many cases medialization can be reached by vocal fold injection (vocal fold augmentation). Various substances of different consistency and residence time in the tissue are available and allow selecting the suitable substance for each individual case. Vocal fold injections are performed under local or brief general anesthesia.
Surgical procedures to center the paralyzed vocal fold are required when augmentation alone is not sufficient. Two procedures are mainly used: Medialization of the vocal fold from the outside by inserting a “stamp” between vocal fold and thyroid cartilage (Thyroplasty type I after Isshiki, with the body’s own cartilage, silicone, titanium clamps or Goretex strips) and arytenoid adduction with special sutures. Both procedures can be combined.
Permanently impaired respiration during physical exertion may necessitate glottic enlargement surgery. As this surgery poses a risk for voice quality and is usually irreversible, glottic enlargement surgeries should be performed only when mobility of the larynx is unlikely to return after healing of at least one laryngeal nerve. Due to the slow growth rate of the nerve, a healing period of at least 6 to 12 months, is recommended. A larynx EMG might allow an earlier prognosis and could reduce the waiting period for a glottic enlargement surgery in some cases.
A partially reversible lateral fixation of the vocal fold with a special suture (Lichtenberger’s technique) and various irreversible glottic enlargement techniques are distinguished. In the latter, one (rarely both) of the vocal folds is incised with a laser beam and part of the vocal fold and/or the arytenoid cartilage removed. Enlargement of the respiratory pathway almost always causes a certain deterioration of the voice because complete vocal fold closure is no longer possible. The more extensive the enlargement, the weaker the voice. Thus it is necessary to find a good compromise between improving respiration and preserving the voice.
Preservation of the voice while improving respiration requires at least a partial recovery of vocal fold mobility. Research results indicate that dynamic therapeutic approaches will be possible soon.
In the future, recurrent laryngeal nerve paralysis may be treated with a laryngeal pacemaker. This device electrically stimulates the responsible muscle respectively nerve within the larynx, which leads to an opening of the vocal folds. First human studies had already been performed in US in the late 90s   which proved the concept of laryngeal pacing. Furthermore, a new approach has been successfully tested in a human study by a European group.
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