Vocal Cord Paralysis

Immobility of one or both vocal folds due to interruption of the motor supply from the vagus nerve through its recurrent laryngeal branch, or of the superior laryngeal nerve, or due to a central lesion. The term vocal fold paralysis is preferred to cord, and immobility from cricoarytenoid joint fixation or posterior glottic scarring must be distinguished from true neurological paralysis, since the management differs completely.

Anatomy of the recurrent laryngeal nerve, which explains the causes

Both recurrent laryngeal nerves arise from the vagus and take an asymmetric course.

• The left nerve arises at the level of the aortic arch, loops beneath the arch posterior to the ligamentum arteriosum, and ascends in the tracheo oesophageal groove to the larynx. Its long intrathoracic course exposes it to bronchial carcinoma, mediastinal nodes, aortic aneurysm, left atrial enlargement and thoracic surgery, and explains why left sided palsy is around twice as common as right and why left palsy demands imaging of the chest to the level of the arch.
• The right nerve arises at the level of the subclavian artery, loops beneath it, and ascends in the tracheo oesophageal groove. Its shorter course means right palsy is more often related to neck and thyroid pathology.
• A non recurrent right laryngeal nerve occurs in around 0.5 to 1 percent, associated with an aberrant right subclavian artery, and is a well recognised cause of injury during thyroid surgery because it is not looked for in the expected position.
• Both nerves run in close relation to the inferior thyroid artery and enter the larynx behind the cricothyroid joint, passing under the inferior constrictor at the ligament of Berry, which is the commonest site of injury during thyroidectomy.

Muscle supply and the position of the paralysed fold

The recurrent laryngeal nerve supplies all intrinsic laryngeal muscles except cricothyroid, which is supplied by the external branch of the superior laryngeal nerve. Posterior cricoarytenoid is the sole abductor.

Complete recurrent laryngeal nerve palsy therefore produces a fold that lies in a paramedian or slightly lateral position with loss of both abduction and adduction, with the cricothyroid maintaining some tension.

The classical Semon law teaching that abductor fibres fail before adductor fibres is not supported by modern understanding and should not be used to predict fold position.

Superior laryngeal nerve palsy produces loss of cricothyroid function with loss of pitch control and vocal fatigue, a normally mobile but flaccid fold with a rotated posterior commissure and an oblique glottis, and reduced sensation of the supraglottis with a risk of aspiration.

Causes

• Iatrogenic, which is the commonest overall, from thyroidectomy which accounts for the largest share, parathyroidectomy, anterior cervical spine surgery, carotid endarterectomy, cardiac and aortic surgery, oesophagectomy, thoracic surgery, patent ductus ligation in neonates, and prolonged intubation.
• Malignancy: bronchial carcinoma, thyroid carcinoma, oesophageal carcinoma, mediastinal lymphoma, nasopharyngeal carcinoma with skull base involvement, and metastatic disease.
• Idiopathic in around 20 percent, presumed viral neuropathy, with a substantial rate of spontaneous recovery.
• Neurological: stroke, particularly lateral medullary syndrome, multiple sclerosis, motor neurone disease, Guillain Barré syndrome, Parkinson disease, multiple system atrophy, and Arnold Chiari malformation in children.
• Trauma: blunt and penetrating neck injury, and intubation with cuff pressure injury.
• Cardiovascular: aortic arch aneurysm, left atrial enlargement in mitral stenosis producing Ortner syndrome, and pulmonary hypertension.
• Infective and inflammatory: tuberculosis, syphilis, Lyme disease, sarcoidosis, vasculitis, and viral neuritis.
• Neurotoxic drugs: vincristine, cisplatin.

Bilateral palsy is most often iatrogenic after thyroid surgery, and is an airway problem rather than a voice problem, since both folds sit near the midline and the voice may be surprisingly good while the airway is critically narrow.

Unilateral palsy

• Breathy, weak voice with reduced volume and reduced maximum phonation time.
• Vocal fatigue, running out of breath mid sentence, and inability to project.
• Diplophonia, that is a double tone, from asymmetric fold vibration.
• Weak, bovine cough with loss of the explosive component, because the glottis cannot close to build subglottic pressure.
• Aspiration, particularly of thin liquids, with coughing on drinking. Aspiration is worse with a high vagal lesion, since sensation is also lost.
• Dyspnoea on exertion is mild or absent, since the airway is adequate.
• Choking episodes and recurrent chest infections in the elderly and neurologically impaired.

Bilateral palsy

• Inspiratory stridor and dyspnoea, worse on exertion and often first noticed on exercise or during an upper respiratory infection when a small amount of additional oedema tips the airway into obstruction.
• A voice that is often near normal or only mildly weak, which is a dangerous paradox: the patient with the good voice and the stridor has the airway emergency.
• Progressive exercise limitation.
• Aspiration is less prominent than in unilateral palsy.

Examination

• Assess voice quality, maximum phonation time, which is normally above 15 seconds in an adult and is shortened in glottic insufficiency, and the strength of the cough.
• Assess the airway, including stridor at rest and on exertion.
• Full cranial nerve examination, since a high vagal lesion involves the pharyngeal branch with palatal weakness, and lesions at the skull base involve cranial nerves IX, XI and XII and the sympathetic chain with Horner syndrome.
• Neck examination for thyroid masses, nodes and scars.
• Chest examination.

• Flexible nasolaryngoscopy, which is the essential first investigation. Assess fold position, mobility, symmetry, glottic gap during phonation, arytenoid position and any passive movement. Record whether the fold is in a median, paramedian or lateral position.
• Laryngeal electromyography, which distinguishes true neurological paralysis from cricoarytenoid joint fixation, distinguishes recurrent laryngeal from superior laryngeal nerve involvement, provides prognostic information about the likelihood of recovery, and is best performed between 4 weeks and 6 months after onset. Fibrillation potentials indicate denervation; polyphasic potentials indicate reinnervation and a favourable outlook; electrical silence with no motor unit potentials indicates a poor prognosis for recovery.
• Direct laryngoscopy under general anaesthesia with palpation of the cricoarytenoid joint, which distinguishes fixation from paralysis. This should be performed before any permanent procedure.
• Videostroboscopy to assess the mucosal wave, glottic closure and compensatory patterns.
• Imaging is mandatory in every patient with an unexplained palsy, since a proportion have an occult malignancy:
• Contrast enhanced computed tomography from the skull base to the level of the aortic arch on the left, and from the skull base to the thoracic inlet on the right, following the full course of the relevant nerve. Failing to image low enough on the left is a recognised cause of missed bronchial carcinoma.
• Chest radiography is insufficient as the sole imaging investigation.
• Magnetic resonance imaging of the brain and skull base where a central or high vagal lesion is suspected, or where computed tomography is negative.
• Ultrasound of the thyroid and neck with fine needle aspiration of any suspicious lesion.
• Barium swallow or flexible endoscopic evaluation of swallowing, and videofluoroscopy, to quantify aspiration and to guide feeding.
• Blood tests: full blood count, glucose, thyroid function, autoimmune screen, Lyme serology, angiotensin converting enzyme, and syphilis serology in appropriate settings.
• Panendoscopy where malignancy is suspected but not localised on imaging.

Management is determined by whether the palsy is unilateral or bilateral, by the severity of symptoms, and by whether recovery is still possible.

Timing

Spontaneous recovery occurs in a substantial proportion within 6 to 12 months, particularly in idiopathic and traction injuries. Permanent procedures are therefore usually deferred for 9 to 12 months, unless electromyography indicates no prospect of recovery, the nerve is known to have been transected, or symptoms are intolerable. Temporary procedures are used in the waiting period.

Unilateral palsy, conservative management

• Voice therapy with a speech and language therapist, which is the first line treatment. It improves glottic closure through compensatory strategies, optimises breath support, reduces supraglottic hyperfunction, and in a proportion of patients produces a satisfactory voice without surgery.
• Swallowing therapy with postural manoeuvres including head turn to the paralysed side and chin tuck, effortful swallow and supraglottic swallow, and diet modification with thickened fluids where aspiration is demonstrated.
• Manage reflux and optimise hydration.
• Treat the underlying cause.

Unilateral palsy, temporary procedures

• Injection laryngoplasty, that is medialisation of the paralysed fold by injecting material into the paraglottic space lateral to the vocalis muscle. Performed transorally, transcutaneously through the cricothyroid or thyrohyoid membrane under local anaesthesia with endoscopic guidance, or under general anaesthesia at microlaryngoscopy.
• Temporary materials: carboxymethylcellulose gel lasting 2 to 3 months, and hyaluronic acid lasting 3 to 6 months.
• Longer lasting: calcium hydroxylapatite lasting 12 to 24 months, and autologous fat, which is unpredictable in resorption.
• Early injection within the first weeks after onset improves voice and swallowing during the waiting period, reduces aspiration and pneumonia in high risk patients, and appears to reduce the eventual need for permanent surgery, which is an argument against simply waiting.
• Avoid injecting into the superficial lamina propria, which causes permanent stiffness and loss of the mucosal wave.

Unilateral palsy, permanent procedures

Indicated after 9 to 12 months without recovery, or earlier where recovery is not expected.

• Type I thyroplasty, that is medialisation laryngoplasty: a window is cut in the thyroid cartilage and a shaped implant of silastic, Gore-Tex or titanium is placed to displace the fold medially. Performed under local anaesthesia with sedation so that voice can be assessed intraoperatively and the implant adjusted, which is a genuine advantage. It is reversible and adjustable, and it does not violate the vocal fold mucosa.
• Arytenoid adduction, in which a suture is placed through the muscular process of the arytenoid and pulled anteriorly to rotate the vocal process medially and lower the fold. Added to thyroplasty where there is a large posterior glottic gap or a vertical height difference between the folds, which thyroplasty alone cannot correct.
• Laryngeal reinnervation with an ansa cervicalis to recurrent laryngeal nerve anastomosis, which restores tone and bulk to the thyroarytenoid muscle without restoring purposeful movement. It produces a durable good voice, is particularly attractive in younger patients since it avoids an implant that may need revision over decades, but takes 6 to 12 months to take effect.
• Combination approaches are common.

Bilateral palsy

The problem is the airway, and the fundamental trade off is that any procedure that enlarges the glottic airway worsens the voice. This must be discussed explicitly with the patient before any intervention.

• Acute presentation with stridor: assess urgently, give humidified oxygen, nebulised adrenaline and intravenous dexamethasone 8 mg as temporising measures, and prepare for intubation or tracheostomy. Involve senior anaesthetic support.
• Tracheostomy, which relieves the obstruction immediately, preserves the voice completely when a speaking valve is used, and is fully reversible if recovery occurs. It remains the correct initial choice in the acute setting and in patients who may recover, and it should not be regarded as a failure.
• Observation with tracheostomy for 9 to 12 months to allow for recovery, with serial laryngoscopy and electromyography.

Definitive airway procedures, all of which trade voice for airway:

• Cordotomy, that is transverse laser division of the posterior vocal fold at the vocal process, which enlarges the posterior glottis. It is relatively quick, can be repeated, and produces a moderate voice deterioration.
• Partial or total arytenoidectomy, endoscopic or open, which produces a larger airway with greater voice loss and a higher risk of aspiration.
• Posterior cordotomy combined with medial arytenoidectomy.
• Suture lateralisation of the vocal fold, which is reversible and is particularly suitable in children and where recovery remains possible.
• Laryngeal reinnervation and selective reinnervation procedures, which aim to restore abduction, are performed in a small number of specialist centres with encouraging results in selected patients.
• Botulinum toxin injection into the adductor muscles as a temporising measure to widen the glottis, useful as a trial before a permanent procedure.

Aspiration management

• Swallowing assessment with instrumental evaluation.
• Diet modification and swallow manoeuvres.
• Injection laryngoplasty, which improves glottic closure and reduces aspiration.
• Nasogastric or gastrostomy feeding where aspiration is severe, particularly in high vagal lesions with sensory loss and in neurologically impaired patients.
• In intractable aspiration with recurrent pneumonia, laryngotracheal separation or total laryngectomy may be required as a last resort in a patient with no useful voice.

Follow up

Serial laryngoscopy at 3 monthly intervals during the observation period, with repeat electromyography where prognosis is uncertain. Continue voice therapy throughout. Where the cause was not identified initially, repeat imaging at 6 to 12 months, since an occult malignancy may become apparent, and this repeat imaging is frequently omitted in patients labelled idiopathic.