Airway Glottic Insufficiency

Etiology

Vocal fold paralysis, which is characterized by complete immobility, and vocal fold paresis, which entails weakness or partial immobility of the vocal folds, are the 2 most prevalent contributors to glottic insufficiency. Vocal fold immobility is not a standalone diagnosis but rather a physical observation that necessitates investigating the underlying cause. In the current and most comprehensive case series, surgical injury is the leading cause of unilateral vocal cord paralysis.[1] However, it is essential to thoroughly evaluate patients who have not undergone prior surgery or intubation before considering the paresis as idiopathic. The evaluation process must exclude central and peripheral neurological factors, infectious etiologies, and neoplasms affecting the central nervous system, head, neck, and upper chest. Any condition affecting the recurrent laryngeal nerve pathway from the brainstem to the larynx has the potential to result in vocal fold weakness and should be thoroughly investigated.

Additional factors contributing to glottic insufficiency encompass presbylaryngeus, an age-related central bowing of the vocal folds, and conditions such as sulcus vocalis, vocal fold nodules, and neoplasms. Central and peripheral neurological injuries, intubation-related trauma, arytenoid trauma, infections, scarring, and vocal fold deformities represent additional potential causes. Furthermore, glottic insufficiency can be congenital, idiopathic, or a secondary effect of iatrogenic factors such as glottic tumor excision.

Epidemiology

Comprehensive epidemiological data regarding glottic insufficiency is limited, likely due to the multitude of complex and diverse contributing factors, as well as the potential for underdiagnosis. Classically, the risk of vocal fold paresis after thyroid surgery has been reported as 1%. However, with the implementation of more sensitive neuromonitoring and measurements, up to 5.6% of patients may exhibit demonstrable weakness after thyroidectomy. Presbylaryngeus exhibits an increasing incidence with age and has been documented in 8% to 10% of individuals in certain geriatric facilities. Genuine idiopathic vocal fold paresis or paralysis has been estimated at 1 case per 100,000 individuals annually, as reported in a multi-institutional population study.[2][3][4]

Pathophysiology

One of the functions of the vocal folds is to protect the lower airway and lungs, particularly during the process of swallowing. When the vocal fold cannot attain its complete median position, it compromises the protective function of the glottis. Partial or complete compensation may also occur either by the contralateral or false vocal folds.[5]

The vocal folds regulate airflow and pressure while producing voice through vibration and enabling meaningful phonation. The production of vocal notes involves repeated contact, vibratory movements, and mucosal wave patterns of the vocal folds. Glottic insufficiency disrupts these functions by causing incomplete contact between the phonatory surfaces of the vocal folds or alterations in the amplitude of the typical fluid-wave motion. This can result in potential aspiration, compromised vocal function, and diminished projection.

History and Physical

Glottic insufficiency manifests in various symptoms. The clinician should perform an informal assessment of the patient's voice during the initial consultation. Patients may exhibit a feeble voice and report vocal weakness, strenuous or painful phonation, known as odynophonia, breathlessness while speaking, and a weak cough, also referred to as bovine cough, which results from inadequate vocal fold adduction. A patient's medical history might include dysphagia, coughing, or choking episodes when swallowing, especially with thin liquids, or recurrent chest infections attributed to aspiration. Clinicians should be vigilant for "red-flag" symptoms such as unilateral throat pain, referred otalgia, dysphagia, unexplained weight loss, or the presence of a neck mass, as these could indicate a neoplastic etiology.[6]

When assessing a patient with glottic insufficiency, it is essential to gather additional medical history to identify potential contributing factors. Healthcare providers should specifically inquire patients about any recent surgeries, especially those involving the cervical, thyroid, or thoracic regions, as well as any instances of extended intubation for any medical reason. Furthermore, any history of cervical or whiplash trauma should be elicited.

Understanding a patient's vocal requirements, especially if their voice plays a significant role in their social or professional life, such as for professional singers, teachers, or preachers, is essential. This information can assist in determining the most suitable intervention for them. Patients with even minor dysphonic symptoms can be disproportionally impacted if their livelihood depends on their voice. Therefore, gathering patients' comprehensive neurological and cardiovascular history is essential, as conditions such as stroke, seizure disorders, multiple sclerosis, or other neurological conditions can influence their voice and cranial nerve functions.

The GRBAS scale is a widely used tool for assessing the vocal health of individuals, and it evaluates vocal characteristics by assessing grade, roughness, breathiness, asthenia, and strain. This tool can be used in a clinical setting to assess and rate patients' voices.[7] Although the GRBAS scale requires trained perceptual evaluation, it is helpful for comparing both before and after interventions.

Before conducting a targeted assessment of the phonatory apparatus, a thorough examination of the ear, nose, and throat is necessary. This includes utilizing flexible laryngoscopy to assess the larynx for any anatomical abnormalities. During the physical examination, potential extrinsic causes of dysphonia, such as neck masses, nasal polyps, or enlarged tonsils, may be identified, as these factors can contribute to alterations in voice quality. Intrinsic laryngeal pathologies, such as chronic laryngitis or singer's nodules, may also be detected, influencing phonatory symptoms directly or indirectly. Palatal paralysis and ipsilateral vocal fold paralysis suggest a high vagal lesion. A thorough cranial nerve examination should be conducted to assess the potential involvement of other cranial nerves and exclude an elevated lesion.

Laryngeal palpation can be conducted to assess for tenderness, flexibility, or excessive tension, which can assist in ruling out muscle tension dysphonia. The patient can be instructed to perform the "ee-sniff" maneuver to evaluate the cricoarytenoid joint. Simultaneously, the examiner can position their fingers behind the thyroid alar to directly palpate the joint. In instances of vocal fold paralysis, no movement is observed on the ipsilateral side, while the examiner may feel a gentle tap on their finger on the contralateral side.[8]

Evaluation

Direct visualization of the glottis is the most sensitive and specific approach for assessing vocal fold movement abnormalities. However, indirect visualization with concomitant videostroboscopy is the most practical and clinically useful method.[9]

Visualization can be initiated using flexible laryngoscopy in a clinical setting. This enables the assessment of vocal fold asymmetry, bowing, and identifying lesions such as vocal fold scarring or sulcus vocalis, which could contribute to vocal fold closure issues. Careful observation of the exact vocal cord positioning is essential, as it may indicate the level of injury. For instance, a paramedian positioning of the vocal cords suggests injury at the level of the recurrent laryngeal nerve. In contrast, lateral positioning indicates potential injury to both the recurrent and superior laryngeal nerves. This indicates either a high vagal injury or a central nervous system lesion, such as a stroke.

Videostroboscopy facilitates the assessment of the dynamic functioning of the vocal folds, enabling the detection of subtle abnormalities in mucosal motion. This method also provides a means to assess functional deficits associated with symptoms such as breathy phonation.

Serology tests usually provide limited value when assessing glottic insufficiency. However, if a patient's symptoms indicate a systemic disease as the underlying cause of their glottic insufficiency, especially if there is suspicion of conditions such as rheumatoid arthritis or other autoimmune disorders, it becomes essential to obtain relevant serology tests.

Vocal fold immobility is a physical observation that necessitates further investigation to identify its underlying cause. In many cases, no identifiable cause is evident during the initial consultation. A contrast-enhanced computed tomography or magnetic resonance imaging from the level of the skull base down to the diaphragm may be performed to assess for any lesions along the entire course of the recurrent laryngeal nerve and the vagus nerve in the neck and chest.

Laryngeal electromyography should be considered if there is uncertainty regarding the type of vocal cord immobility. This procedure aids in differentiating between motion impairment caused by structural issues, such as mechanical fixation, dislocation, or ankylosis of the cricoarytenoid joint, leading to closure defects, and motion impairment caused by vocal fold denervation.

Due to its limited sensitivity, acoustic voice recording is less reliable for screening phonatory apparatus pathology. However, this sound recording technique proves valuable in facilitating the objective analysis of voice outcomes and subsequent rehabilitation. Clinicians can compare results based on computer-based analysis of acoustic signals rather than relying solely on subjective reports from either the patient or the examiner.[10]

Treatment / Management

Restoring glottic competence can enhance voice quality, alleviate dysphagia, and lower the risk of aspiration. Addressing these symptoms can improve a patient's overall quality of life. To tailor an appropriate treatment approach, management decisions should consider patient characteristics such as age, occupation, social circumstances, and individual preferences.

Voice therapy usually plays a significant role irrespective of the underlying etiology of glottic insufficiency. Patients with unilateral vocal fold paralysis may find voice therapy to be their initial management option, given that up to 60% of cases can resolve spontaneously.[11] Glottic scarring and sulcus vocalis can lead to unpredictable surgical outcomes. Therefore, conservative approaches such as antireflux medications, steroids, and voice therapy are valuable options for initial trial therapy. Although voice therapy can be effective alone, it is also helpful as an adjunct to phonosurgical management.(A1)

Surgical interventions for glottic insufficiency due to unilateral paralysis or paresis aim to medialize the affected vocal fold, enabling proper glottic closure during phonation and improving lower airway protection. Various techniques are utilized to achieve this goal, including injection augmentation, medialization thyroplasty or type 1 thyroplasty, laryngeal reinnervation, and arytenoid adduction.

Injection augmentation utilizes various materials that can be injected into the vocal fold to restore its bulk and form. This method yields immediate results and represents a more minimally invasive option compared to laryngeal framework surgery. Currently used materials include absorbable hemostatic powder, collagen derived from bovine and human sources, fat, dermal fillers such as calcium hydroxylapatite, hyaluronic acid gels, and micro-ionized acellular dermis.[12] Although Teflon was formerly used as an injectable agent, it has since been associated with complications, including foreign body giant cell granulomas and persistent vocal deficits, even after corrective procedures. Injection augmentation can be performed under general anesthesia in the operating room or using local anesthesia with the patient fully awake in the office.[11](A1)

In medialization thyroplasty, the vocal cord's position is medialized through an external approach, during which a permanent implant is placed intraoperatively through a thyroid cartilage window. This procedure is usually conducted with conscious sedation and intraoperative voice analysis, although the patient is under heavy sedation. Medialization thyroplasty, utilizing various implants, such as expanded polytetrafluoroethylene (E-PTFE) or Silastic, is considered the gold standard treatment for large glottic gaps and serves as the primary surgical intervention for unilateral vocal cord palsy.[13](B3)

Arytenoid adduction is a surgical procedure designed to restore the correct position of the vocal process by recreating the pull of the lateral cricoarytenoid muscle. This repositioning of the vocal process helps medializing and elevating the affected vocal fold. Arytenoid adduction is often used as an adjunct procedure when there is impaired contact between the vocal processes but some residual movement of the vocal folds. This procedure is not commonly performed as a standalone technique but can be valuable when combined with other surgical techniques to optimize vocal fold function and enhance glottic closure.

Nonselective laryngeal reinnervation involves anastomosing the ansa cervicalis to the recurrent laryngeal nerve. This procedure aims to maintain the bulk and tone of the thyroarytenoid muscle. Nonselective laryngeal reinnervation can yield excellent vocal function because the vocal cords remain pliable compared to other techniques.

When addressing sulcus vocalis and vocal fold scars, epithelium-freeing techniques are frequently used in conjunction with injection augmentation, medialization, and laryngoplasty. These techniques are directed toward enhancing the vibratory function of the vocal fold. By releasing the epithelium and addressing the underlying scar tissue or tissue deficiency, these techniques can help optimize vocal fold motion and enhance vocal quality.[14](B3)

Differential Diagnosis

The differential diagnosis for glottic insufficiency or airway glottic insufficiency includes the following conditions:

• Laryngeal cancer
• Vocal cord nodules and polyps 
• Acute corditis vocalis
• Hypotonic voice disorders
• Reinke's edema
• Laryngeal granuloma
• Functional aphonia
• Spasmodic dysphonia
• Dysphonia plicae ventricularis
• Hypotonic voice disorders
• Essential tremor

Prognosis

In a case series conducted by Omori et al, patients with glottic insufficiency dysphonia were examined to explore the impact of glottal gap size and etiology on vocal function.[15] The study revealed that vocal fold palsy was associated with the largest glottal gaps and notably limited vocal function than vocal fold atrophy and sulcus vocalis. However, similar glottal gap sizes were related to similar vocal functioning, irrespective of the underlying etiology. This suggests that the size of the glottal gap primarily influences vocal function rather than the etiology of glottic insufficiency. 

Vocal function has shown improvement with both medialization thyroplasty and injection augmentation techniques.[16][17][[18][19] Injection augmentation is a safe and clinically effective procedure, yielding similar outcomes whether performed under general anesthesia or in a clinic setting. Injecting an intentionally resorbable material such as hyaluronic acid, which typically resorbs within approximately 3 months in the vocal fold, can substantially benefit both voice quality and airway protection. Although full recovery is anticipated in most cases of idiopathic or post-viral vocal fold paralysis and paresis, it may take up to 1 year after paralysis.[20][21][22]

Success with vocal fold fat injections can yield variable results because of the unpredictable reabsorption of fat during the early weeks. A recommended practice is to over-inject by approximately 30% to account for the expected graft loss. Patients should be aware that they may experience dysphonia for around 3 weeks after the procedure.[11] According to a recent Cochrane systematic review, no evidence suggests that injectable agents are superior for patients with unilateral vocal fold palsy.[11]

Medialization thyroplasty has shown favorable outcomes. Although the short-term vocal function results of augmentation may be satisfactory, medialization thyroplasty might offer superior long-term results, especially for larger glottic caps.[13][23][24][25] Limited data is available on the long-term effectiveness of injection augmentation. Dominguez et al reported that although initial voice outcomes were comparable between fat-injection and medialization thyroplasty groups, the effects of the fat injections diminished over time, leading to worse Voice-Handicap Index and Glottal Index scores.[26]

Complications

Besides its effect on voice quality, glottic insufficiency can contribute to dysphagia and aspiration, which may result in recurrent lower respiratory tract infections. Although medialization thyroplasty is predominantly considered a phonosurgical procedure, it has the potential to improve swallow function and prevent potential life-threatening consequences of aspiration. In a case series involving 84 patients with impaired unilateral vocal fold motion, all of them experienced dysphonia, and 61% reported difficulty swallowing.[27]