Neurologic Considerations in Vocal Cord Paralysis
In a patient with paralyzed vocal cords, the primary neurologic considerations are identifying the anatomic level of nerve injury (central versus peripheral), determining the underlying etiology (iatrogenic, neoplastic, or idiopathic), and distinguishing true neurologic paralysis from mechanical immobility using laryngeal electromyography. 1, 2
Anatomic Localization of Neurologic Injury
The recurrent laryngeal nerve (RLN) innervates all intrinsic laryngeal muscles except the cricothyroid, including the thyroarytenoid, lateral cricoarytenoid, interarytenoid, and posterior cricoarytenoid muscles 3. The entire course of the nerve from the brainstem through the skull base, neck, and mediastinum to the aortopulmonary window must be evaluated 2.
Central versus peripheral causes:
- Central causes include vagal paragangliomas at the skull base, Arnold-Chiari malformations (especially in neonates with bilateral paralysis), brainstem dysfunction, and neuromuscular disorders 1, 4
- Peripheral causes include surgical injury (particularly thyroidectomy), trauma, malignancy along the nerve course, and esophageal compression of the RLN 1, 5
Diagnostic Algorithm
Step 1: Confirm diagnosis with laryngoscopy to evaluate vocal cord position and mobility 2. This is essential before proceeding with further workup.
Step 2: Distinguish neurologic from mechanical causes using laryngeal electromyography (LEMG), which shows neurological impairment in 86-92% of symptomatic patients with suspected vocal fold paresis 1. LEMG can identify unilateral (60%), bilateral (40%), and contralateral neuropathy (26%) in these patients 1. This distinction is critical because direct tumor invasion can cause mechanical immobility through muscle infiltration rather than neural compromise 3.
Step 3: Imaging to identify the etiology:
- CT with contrast of the neck extended to the aortopulmonary window for initial evaluation, visualizing bony integrity of the skull base and the entire RLN course 2
- MRI when intracranial or skull base lesions (such as vagal paragangliomas) are suspected 2
Common Etiologies by Frequency
The most common causes are idiopathic (31%), tumors (31%), and surgical injury (29%) 6. However, malignancy must be excluded before labeling any case as idiopathic 6.
Surgical injury:
- Thyroidectomy is the most common iatrogenic cause, with bilateral RLN injury potentially causing catastrophic airway obstruction requiring tracheostomy 1
- Patent ductus arteriosus repair and tracheoesophageal fistula repair are associated with unilateral paralysis 4
Neoplastic causes:
- Vagal paragangliomas cause paralysis through compression or infiltration of the vagus nerve 1
- In patients with SDHD-related head and neck paragangliomas, vagal lesions should rarely be resected due to high risk of vocal cord paralysis 1
- Bilateral surgical interventions on vagal paragangliomas are contraindicated as bilateral paralysis often necessitates tracheostomy 1
Emerging considerations:
- SARS-CoV-2 infection may cause bilateral vocal cord paralysis as a neuropathic sequela, presenting 9 days after mild infection 7
Critical Pitfalls to Avoid
Do not mistake all arytenoid motion for normal vocal cord function during flexible laryngoscopy, as passive movement can be misinterpreted as active cord mobility 4.
Do not assume bilateral immobility is always neurologic - esophageal compression from achalasia can cause reversible bilateral paralysis through RLN compression, which resolves within 1 week after decompression 5.
In neonates with inspiratory stridor and Arnold-Chiari malformation, assume bilateral abductor vocal cord paralysis until proven otherwise 4.
Unilateral versus Bilateral Paralysis: Clinical Implications
Unilateral paralysis presents with hoarse voice, breathy cry, and aspiration risk, with symptoms typically evident within 24 hours of injury 8, 4.
Bilateral paralysis presents with stridor ranging from mild with exertion to acute airway obstruction, and patients have a fixed glottic size making airway edema potentially catastrophic 8. These patients require tracheostomy consideration, particularly in infants, though sophisticated cardiorespiratory monitoring may allow delayed intervention 4.
Perioperative Neurologic Considerations
Intubation-related vocal cord paralysis results from prolonged pressure on the RLN and can be temporary (resolving within 6 months) or permanent 8. Contributing factors include endotracheal tube size, cuff location, and cuff pressure 8. For patients with known bilateral paralysis, avoid intubation when possible, use smaller tubes when necessary, administer perioperative corticosteroids, and provide enhanced postoperative monitoring 8.