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
Symptoms from RLN damageSymptoms from SLN damage Rough voice quality Breathy voice quality Vocal fold bowing Decreased vocal fold mobility Glottal insufficiency Hyperfunction Vocal fatigue or mutism Reduced vocal stamina Changes in voice pitch or pitch range Difficulty varying pitch at a quick rate Difficulty projecting voice or speaking loudly or in noisy environments Throat pain Bouts of choking Diplophonia Swallowing difficulties Chronic coughing Globus sensation Hypersensitivity or abnormal sensation Vocal fold spasms Pain from vocal use Loss of voice in high pitch ranges
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. 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.
Congenital Congenital conditions that are implicated in VFP include neurological disorders like hydrocephalus and Arnold-Chiari malformation, dysmorphic neurological disorders such as Moebius syndrome or Goldenhar Syndrome, anatomical abnormalities such as a tracheoesophageal fistula, vascular anomalies (e.g. vascular ring) affecting the vocal mechanism, syndromes affecting brainstem function or atrophic diseases such as Charcot-Marie-Tooth.
In the absence of imaging, either invasive (e.g. laryngoscopy) or non-invasive (e.g. computed tomography scan), congenital VFP can be detected in infants through the presence of stridor (i.e. a high-pitched wheezing resulting from a blockage in the larynx or trachea), difficulties feeding, an abnormal sounding cry or excessive hoarseness.
Recovery from congenital VFP varies and is reliant on the severity of the condition. Some cases of VFP recover spontaneously, often within the first year. If the paresis is persistent, surgical options such as vocal fold injections or tracheotomy can be taken into consideration.
Infection Many viral infections have been reported as a cause for VF paresis, including herpes simplex virus, Epstein-Barr virus, Varicella-Zoster, cytomegalovirus, HIV, West Nile virus, and upper respiratory infection. Bacterial infections have also been reported to cause VF paresis, such as syphilis and Lyme disease.
Tumors When abnormal cells group together in the body, they are said to form a tumor. Tumors can be either malignant (cancerous) or benign (non-cancerous). Tumors may lead to paralysis of the vocal folds when they affect the recurrent laryngeal nerves (RLNs) either directly or indirectly: RLN paralysis can be caused by tumors of the thyroid, lung, esophagus, and mediastinum. Radiation as a treatment for malignant head and neck tumors can reduce the number of blood vessels in the treatment area and lead to scarring. In some cases, this can paralyze the vagus nerve, of which the RLNs are branches. Tumors of the vagus nerve, called vagal neurilemmomas, can also paralyze the vocal folds.
Trauma VF paresis can result from trauma to one of more laryngeal nerves during intubation, surgery (e.g. thyroidectomy, parathyroidectomy, spine surgery, carotid endarterectomy, vagal nerve stimulator implantation), injection of botulinum neurotoxin, or penetrating neck trauma.
Thyroid disease Causes of VF paresis also include diseases of the thyroid gland, such as hypothyroidism, goiter, and thyroiditis.
Systemic neurologic diseases
Several neurological diseases can cause VF paresis including: Myasthenia Gravis (MG), a rare neuromuscular autoimmune disease. MG's dominant characteristic is muscles weakness including facial, jaw, pharyngeal and laryngeal muscles. Charcot-Marie-Tooth (CMT), a neurological heredity disease that affects both motor and sensory functions. CMT affects the nerve cells and interrupts the transmission of nerve impulses as it concerns the axons and the myelination of the nerve cells. Multiple Sclerosis (MS), which is an autoimmune disease that damages the myelin sheet surrounding the axons of the cranial nerves and the spinal nerves. There are several types of MS depending on the course of the disease. Spinocerebellar Degeneration, a term that refers to a rare yet diverse chronic disease that affects the brain and the spinal cord. Spinocerebellar Degeneration is usually an inherited progressive disease; however, toxicity and vitamin deficiency can result in the acquired type of cerebellar degeneration disease.
Additionally, there are pieces of evidence that some Systemic Rheumatological Diseases such as sarcoidosis, rheumatoid, scleroderma can result in having VF paresis.
Cardiovascular A rare cause of vocal cord paresis that often presents itself as unexplained hoarseness is cardiovocal syndrome or Ortner's syndrome. Although it was originally identified in patients with left atrial enlargement,Ortner N. Recurrent nerve palsy in patient with mitral stenosis. Wien Klin Wochenschr. 1897;10:753–755. [in German]). the definition has expanded to include aneurysms of the aortic arch, pulmonary hypertension due to mixed connective tissue disease,M. Hirata et al, (2018) Cardiovocal syndrome (Ortner syndrome) associated with secondary pulmonary arterial hypertension in a patient with mixed connective tissue disease, Modern Rheumatology Case Reports, 2:1, 54-58 or aberrant subclavian artery syndrome among other causes of left recurrent laryngeal nerve palsy with cardiovascular origin.
Diagnosis There are a variety of ways to diagnose vocal fold paralysis. Important indications of possible causes can be revealed in the patient's medical history, which may inform which diagnostic approach is taken. 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.
An auditory-perceptual evaluation is conducted by a Speech-Language Pathologist (S-LP), and allows changes in voice quality to be monitored over time. There are two scales which can be used to subjectively measure voice quality: the GRBAS (grade, roughness, breathiness, asthenia, strain) and the CAPE-V (Consensus Auditory Perceptual Evaluation of Voice). The GRBAS is used to rate the patient's voice quality on 5 dimensions: grade (overall severity), roughness, breathiness, asthenia (weakness) and strain. Each dimension will receive a severity rating from 0 (not present) to 3 (severe). This allows the S-LP to make a judgment about the overall severity of the voice quality. The CAPE-V is used in a similar manner, rating of the dimensions of voice quality on a subjective scale from 0–100, and using this to determine an overall severity score.
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.