Vocal cord paresis, also known as recurrent laryngeal nerve paralysis or vocal fold paralysis, is an injury to one or both recurrent laryngeal nerves (RLNs), which control all intrinsic muscles of the larynx except for the cricothyroid muscle. The RLN is important for speaking, breathing and swallowing.
The primary larynx-related functions of the mainly efferent nerve fiber RLN, include the transmission of nerve signals to the muscles responsible for regulation of the vocal folds' position and tension to enable vocalization, as well as the transmission of sensory 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. This strongly depends on the median or paramedian position of the paralyzed vocal folds. Hoarseness rarely occurs in bilaterally paralyzed vocal folds.
Signs and symptoms
Typically, patients with vocal fold paresis or paralysis are able to identify the onset of their symptoms. The most commonly reported symptom patients with either vocal fold paresis or paralysis make is having a rough voice quality. It is important to note that the symptoms of vocal fold paresis are not specific to the condition and tend to be common symptoms of other voice disorders as well. Vocal fold bowing, decreased vocal fold mobility, especially decreased mobility of the arytenoid cartilage, are often observed in vocal fold paresis. Glottal insufficiency is another common symptom observed in vocal fold paresis. In this case, the vocal folds do not come together properly. Glottal insufficiency may be hard to identify, especially when the area above the vocal folds is hyperfunctional. Hyperfunction may also make it difficult to detect the presence of vocal fold paresis. Hyperfunction of the area above the vocal folds may be considered a sign of glottal insufficiency and potentially, vocal fold paresis.
In some cases, glottal closure may appear to be normal, however, asymmetries in the vocal folds may still be present. Though voice qualities may appear normal in some cases of vocal fold paresis or paralysis, mild differences in tension between the two vocal folds of the larynx can result in changes of voice pitch, intensity and reduced vocal stamina.
Patients with either vocal fold paresis or paralysis may exhibit a breathy voice quality. This voice quality results from the increased activity of the vocal folds to compensate for the immobility of the PCA muscle(s). Patients may need to use more effort than normal when speaking and may find that their voice quiets or grows tired after speaking for a long time. This is known as vocal fatigue. Patients may also complain about having a limited pitch range and trouble varying their pitch at quick rate. It is often difficult for the speaker to project their voice and speak loud enough to be heard in noisy environments, over background noise, or when speaking to someone from a distance. It is possible for symptoms to surface only in situations where the environmental acoustics are poor, such as outdoors. Patients may report feeling pain in the throat or experiencing bouts of choking. A patient presenting with diplophonia is of major concern as this typically means that the mass and tension of their vocal folds are asymmetrical which may also indicate vocal fold paresis.
Swallowing difficulties (dysphagia) are not commonly seen in vocal fold paresis that results from RLN damage. Dysphagia may however, suggest SLN damage. Symptoms of sensory nerve damage include: chronic coughing, the feeling of having a lump in the throat (globus sensation), hypersensitivity or abnormal sensation, spasms of the vocal folds (laryngospasms), dysphagia, pain from vocal use, and voice loss in high pitch ranges. It is possible for both the RLN and the SLN to be damaged simultaneously, so the symptoms of RLN and SLN damage may be seen independently or alongside one another.
If maladaptive compensatory strategies are used more and more to try to offset the voice difficulties, the vocal mechanisms will fatigue and the above symptoms will worsen.
Causes
There are a wide variety of possible causes of vocal fold (VF) paresis, including congenital (i.e. present at birth) causes, infectious causes, tumors, traumatic causes, endocrinologic diseases (i.e. thyroid disease), and systemic neurologic diseases.