Glottic insufficiency is characterized by incomplete closure of the vocal folds when phonating, which causes inappropriate leakage of air through the glottis on attempting to phonate and there is an increased risk of aspiration. A wide range of laryngeal symptoms including dysphonia, dysphagia, and aspiration with recurrent lung infections may result. The causes are equally wide-ranging and can include anything that prevents complete closure of the vocal folds (static or dynamic), such as neoplasms, reactive changes, functional and neurologic changes, focal neurologic deficits, trauma, and many others.
There are a variety of causes of glottic insufficiency; among the most common are unilateral vocal fold paralysis or vocal fold paresis (unilateral or bilateral). Vocal fold immobility is a physical finding rather than a diagnosis. Therefore, it is essential to investigate the underlying cause to determine an underlying diagnosis. The largest case series to date cites the most common cause of unilateral vocal cord paralysis as surgical injury. This finding represents a shift in etiology as historically non-laryngeal malignancy was thought of as the leading cause of unilateral vocal fold paralysis.
Other causes of glottic insufficiency are presbylaryngis, sulcus vocalis, vocal fold nodules or neoplasm, central neurologic injury, peripheral neurologic injury, intubation-related injury, arytenoid trauma, infection, scarring or deformation of the vocal fold, and many others. The latter may be congenital, idiopathic, or secondary to iatrogenic causes such as glottic tumor excision.
A literature search does not reveal any comprehensive epidemiological data on glottic insufficiency; this is likely due to the variable causes and complexity of causes of glottic insufficiency, as well as potential under-diagnosis. It is difficult to perform a meaningful literature review on such a common and widely-variable symptom, as opposed to a definitive diagnosis.
One of the functions of the vocal folds is to protect the lower airway and lungs through their sphincteric action. This protection is particularly crucial during swallowing. The vocal folds also function to control airflow and pressure and to generate voice through vibration and meaningful phonation. A vocal note production is through repeated contact and the vibratory movements of the vocal folds. Glottic insufficiency hampers these functions due to the incomplete contact between the two vocal folds, or through a change in the period or amplitude of the normal fluid-wave motion, which can allow aspiration as well as hamper normal vocal function and projection.
Glottic insufficiency produces a variety of symptoms. From the start of the consultation, the clinician should begin to assess the patient’s voice informally during the initial conversation. The patient's voice may sound weak, and they may complain of a weak voice, of effortful or painful phonation (odynophonia), and may have shortness of breath while talking and have a weak cough (the so-called bovine cough, resulting from the inability to fully adduct the vocal folds). There may be a history of dysphagia or coughing/choking with swallowing, particularly with liquids, or of recurrent chest infections due to aspiration. It is important to seek out “red-flag” symptoms such as unilateral throat pain, dysphagia, weight loss, or neck mass, which may suggest a neoplastic etiology.
Further history to be elicited from the patient should ascertain whether there has been any recent surgery, in particular, cervical, thyroid, or thoracic surgery, or prolonged intubation for any cause. The patient’s vocal needs, whether socially or professionally, e.g., a professional singer or other voice-user, such as a teacher or preacher, should be established as this may help determine the most suitable intervention. Patients with even minor dysphonic symptoms can be disproportionally affected if they use their voice for a living.
The GRBAS (grade, roughness, breathiness, asthenia, and strain) scale is a widely used metric for evaluating vocal health and can be used in the clinic setting to rate the patient’s voice. Though this relies on a trained perceptual evaluation, it may be useful as a comparative tool pre- and post-intervention.
Prior to a focused examination of the phonatory apparatus, a general ear, nose, and throat examination is required, including flexible laryngoscopy to evaluate the larynx fo anatomic abnormalities. This may reveal causes of dysphonia extrinsic to the phonatory apparatus such as neck masses, nasal polyps, enlarged tonsils which can contribute to changes in voice quality, as well as intrinsic laryngeal pathology that can be directly or indirectly related to phonatory symptoms such as chronic laryngitis or singer's nodules. Palatal paralysis associated with an ipsilateral vocal fold paralysis is suggestive of a high vagal lesion. A full cranial nerve examination should also be performed to assess the involvement of other cranial nerves to rule out a high lesion.
Palpation of the larynx to assess for tenderness, suppleness or excessive tension may help in ruling out muscle tension dysphonia as a cause of the patient’s dysphonia. The patient can be asked to carry out the “ee-sniff” maneuver while the examiner slips their fingers behind the thyroid alar to directly palpate the cricoarytenoid joint. Vocal fold paralysis will result in no movement on the ipsilateral side, and a gentle tap felt on the examiner’s finger on the contralateral side.
Directly visualizing the glottis is the most sensitive and specific method for assessing vocal fold movement abnormalities, though indirect visualization with concomitant video stroboscopy is the most practically useful method.
Visualization can start with flexible laryngoscopy in the clinic. Vocal fold asymmetry and bowing may be visualized, as well as lesions such as vocal fold scarring and sulcus vocalis which may be causing a closure deficiency of the vocal folds. The exact vocal cord positioning should be noted and may indicate the level of injury; e.g., a paramedian positioning of the cords is suggestive of injury at the level of the recurrent laryngeal nerve compared with lateral positioning of the cords suggesting both recurrent laryngeal and superior laryngeal nerve injury (indicating either a high vagal injury or a central nervous system lesion such as a stroke).
Video stroboscopy allows assessment of the dynamic functioning of the vocal folds. Subtle abnormalities of mucosal motion can be detected, and functional deficits that accompany symptoms such as breathy phonation can undergo assessment.
Serology tests tend to add little value when evaluating glottic insufficiency, however, should the patient’s symptoms be suggestive of systemic disease as a cause of their glottic insufficiency, particularly if there is suspicion of rheumatoid arthritis or other autoimmune conditions, the relevant serology tests should be obtained.
Vocal fold immobility is a physical finding rather than a diagnosis. It is necessary to determine the underlying cause. Commonly there is no identifiable cause found during the initial consultation. A contrast CT or MRI from the level of the skull base down to the diaphragm may need to be done to assess for any lesions along the full course of the recurrent laryngeal nerve and the vagus nerve in the neck and chest.
Laryngeal electromyography should be a consideration if there is a suspicion of the etiology of the vocal cord immobility. It aids in differentiating between motion impairment due to structural issues such as mechanical fixation, dislocation, and ankylosis of the cricoarytenoid joint which may cause a closure defect, versus motion impairment caused by denervation of the vocal fold.
Due to its poor sensitivity, acoustic voice recording is less useful as a tool for screening phonatory apparatus pathology. However, it helps aid the objective analysis of voice outcomes and subsequent rehabilitation. The clinician can compare results based on computer-based analysis of acoustic signals rather than relying on patient or examiner subjective reporting.
Restoration of glottic competence may improve voice quality, dysphagia, and reduce the risk of aspiration. Addressing these symptoms may improve the patient’s overall quality of life. The patient’s characteristics such as age, occupation, social circumstances as well as their preferences will help dictate management.
Whatever the specific etiology of the glottic insufficiency, voice therapy usually plays a significant role. For unilateral vocal fold paralysis, voice therapy is the initial management choice since up to 60% of cases will resolve spontaneously. For glottic scarring and sulcus vocalis, surgical results tend to be unpredictable and conservative measures of anti-reflux medications, steroids, and voice therapy can serve as initial trial therapy. Voice therapy may be effective alone but can also be useful as an adjunct to surgical management.
Surgical options for glottic insufficiency due to unilateral paralysis or paresis aim to medialize the affected vocal fold such that glottic closure is achievable during phonation and the lower airway is better protected. The techniques employed are Injection augmentation, medialization thyroplasty (type 1 thyroplasty), laryngeal reinnervation, and arytenoid adduction.
Injection augmentation utilizes a variety of materials injected into the vocal fold that provides bulk to restore a more normal form to the vocal fold. It confers the advantage of producing immediate results and is a more minimally invasive option compared with laryngeal framework surgery. Materials currently used include absorbable hemostatic powder, bovine and human-derived collagen, fat, dermal filler (calcium hydroxylapatite), hyaluronic acid gels, and micro-ionized acellular dermis. Teflon has previously been used as an injectable agent, however, it correlated with foreign body giant cell granulomas, and has associations with significant vocal deficits that have persisted even with corrective procedures.
In medialization thyroplasty, the position of the vocal cord is medialized by an external approach in which a permanent implant is placed through a thyroid cartilage window intraoperatively, often with conscious sedation and intra-operative voice analysis (albeit crude, given the patient is heavily sedated). Medialization thyroplasty using various implants, commonly expanded polytetrafluoroethylene (E-PTFE) or Silastic, is deemed the gold standard treatment for large glottic gaps and is the mainstay surgical intervention for unilateral vocal cord palsy.
Arytenoid adduction involves recreating the pull of the lateral cricoarytenoid muscle thus repositioning the vocal process medially. It tends not to be used as the sole procedure but is useful as an adjunct where there is impaired vocal process contact but some residual vocal fold motion.
Non-selective laryngeal reinnervation involves anastomosing the ansa cervicalis to the recurrent laryngeal nerve, with the goal of maintaining the thyroarytenoid muscle bulk and tone. It has the potential for excellent vocal functioning as the vocal cords remain pliable compared with other techniques.
For the treatment of sulcus vocalis and vocal fold scars, along with injection augmentation and medialization and laryngoplasty, which address the glottic gap, epithelium freeing techniques are commonly employed in combination with injection augmentation or implantation to help improve the vibratory function of the vocal fold.
Omori et al. performed a case series of patients with glottic insufficiency dysphonia that studied the influence of glottal gap size and etiology on vocal functioning. They found vocal fold palsy to be associated with the largest glottal gaps and significantly worse vocal function when compared with vocal fold atrophy and sulcus vocalis. However irrespective of the etiology, similar glottal gap sizes were associated with similar vocal functioning, suggesting glottal gap size is the primary influence of vocal function rather than the etiology of the glottic insufficiency.
The vocal function has been shown to improve with both medialization thyroplasty and injection augmentation techniques. [. Injection augmentation is safe and clinically effective and is performable with similar outcomes either under general anesthesia or, if the patient is an appropriate candidate, in a clinic setting. Injection of an intentionally resorbable material such as hyaluronic acid (which resorbs in ~3 months in the vocal fold) can provide significant benefits to both voice and airway protection. This is true even in idiopathic or post-viral vocal fold paralysis and paresis where full recovery is expected in most cases but may be prolonged in nature (up to one year post-paralysis).
Success with vocal fold fat injections tends to be variable due to the unpredictability of reabsorption of the fat in the first few weeks. Over-injection by 30% is required to allow for this implant loss, and patients should understand they will be dysphonic for approximately 3 weeks. As to whether any injectable agents are particularly superior to others, a Cochrane systematic review looking at patients with unilateral vocal fold palsy concluded that there is a current lack of evidence to suggest this.
Medialization thyroplasty has shown good outcomes while short-term vocal function results of augmentation may be good, for larger glottic gaps, medialization thyroplasty may provide superior longer-term results. There is a scarcity of data available as to the long-term effectiveness of injection augmentation. Dominguez et al. ran a case series of eighty-three patients, and they found that although initial voice outcomes were similar in both fat-injection and medialization thyroplasty groups, the effects of the fat injections wore off with time as evidenced by worse voice-handicap index and glottal index scores.
As well as glottic insufficiency affecting voice quality, glottis insufficiency may also cause dysphagia and aspiration with potential for recurrent lower respiratory tract infections. Medialization thyroplasty is predominantly considered a phonosurgical procedure. However, it has the potential to play a role in improving swallow function and preventing potential life-threatening consequences of aspiration. In their case series of 84 patients with unilateral vocal fold motion impairment, all had dysphonia, and 61% experienced swallowing difficulties).
Voice therapy may be effective alone but is also useful as an adjunct to surgery. The voice therapist can educate the patients as to how to efficiently optimize voice production as well as discourage counterproductive compensations that the patient may have developed such as extraneous neck muscle movements on attempting to phonate.
A systematic review of the current literature shows that a significant portion of unilateral vocal fold paralysis patients have dysphagia. In the context of glottic insufficiency, the focus is often on phonosurgery for voice improvement. However, symptoms of dyspnoea, dysphagia, and aspiration may be present in addition to vocal issues and may also be able to be equally addressed with the surgical interventions mentioned herein.
Management options for patients will need to be highly individualized based on a number of factors; the cause of the glottic insufficiency; whether the patient’s glottic insufficiency is likely to improve with time (for example unilateral vocal cord paralysis will improve in many cases which may negate the need for surgical intervention); the patient’s social and occupational factors. For example, a vocal cord palsy patient may be trialed on voice therapy, or have temporizing vocal cord injection augmentation as a first intervention while a professional voice user with a large glottic gap may require the more permanent option of laryngeal framework surgery. These factors are complex, and management of patients with glottic insufficiency is challenging. As such it requires an inter-professional and holistic approach to optimize patient management. As well as the involvement of specialist laryngologist and voice therapist in the patient’s care, other health professionals whose expert knowledge may be necessary for the patient’s care include neurologists, dieticians, nutritionist, nursing staff, psychologists and pharmacists.
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