What are the features and management of recurrent laryngeal nerve (RLN) palsy?

Features and Management of Recurrent Laryngeal Nerve Palsy

Recurrent laryngeal nerve (RLN) palsy presents with symptoms ranging from mild hoarseness in unilateral lesions to stridor and acute airway obstruction in bilateral damage, with potentially catastrophic effects on patient social interaction and occupational status. 1

Clinical Presentation

Unilateral RLN Palsy

• Hoarseness is the most common symptom, occurring in 1.2%-5.0% of cases following procedures like thyroid surgery 1
• Dysphonia ranging from mild to severe paralytic aphonia 2
• Aspiration of food and liquids into the trachea due to impaired airway protection during swallowing 3
• Impaired ability to cough effectively in the early post-injury period 3
• Flaccidity of the ipsilateral vocal fold with loss of abduction and adduction 2

Bilateral RLN Palsy

• Stridor and acute airway obstruction requiring immediate intervention 1
• Presents as a medical emergency due to potential complete airway obstruction 3
• Associated with a definitive biological damage rate of 25% according to Italian health parameters 1

Etiology

Surgical Causes

• Thyroid surgery: RLN paralysis occurs in up to 2.1% of thyroidectomy patients 1
• Anterior cervical spine surgery: Hoarseness immediately following surgery may be as high as 50% 1
• Carotid endarterectomy: Associated with RLN damage in up to 6% of patients 1
• Cardiac surgery: Hoarseness occurs in 17% to 31% of patients, with RLN injury in about 1.4% 1
• Esophagectomy: Only about 25% of patients with left RLN palsy after minimally invasive McKeown esophagectomy fully recover 4

Non-surgical Causes

• Prolonged endotracheal intubation: Direct laryngoscopy shows 94% of patients intubated for more than four days develop laryngeal injury 1
• Short-term intubation for general anesthesia may result in hoarseness and vocal fold pathology in over 50% of cases 1

Anatomical Considerations

• The RLN is a mixed nerve with sensory and motor fibers, originating from the thoracic portion of the vagus nerve 1
• The right RLN lies in a more superficial plane along the lateral esophageal edge and is traditionally considered at higher risk of injury 1
• The left RLN surrounds the aortic arch and is located more deeply in the tracheoesophageal groove 1
• The RLN innervates all intrinsic laryngeal muscles except the cricothyroid muscle 1
• Non-recurrent laryngeal nerve is a rare variant (incidence 0.3-1.6%) observed more frequently on the right side 1

Mechanisms of Injury

• Transection (rarely), clamping, stretching, electrocoagulation, ligature entrapment or ischemia are the main causes 1
• The left recurrent laryngeal nerve is damaged more commonly than the right during cardiac surgery as it extends into the chest and loops under the arch of the aorta 1
• Damage may result from direct physical injury to the nerve or hypothermic injury due to cold cardioplegia during cardiac surgery 1
• In anterior cervical spine surgery, RLNP typically occurs secondary to neurapraxia caused by intraoperative compression or traction on the nerve 5
• Delayed onset of RLNP may be due to small vessel ischemia, vasospasm, or viral resurgence 5

Diagnosis

• Laryngoscopy is essential for diagnosis and should be performed in patients with persistent voice changes 1
• The detection of vocal fold paralysis doubles when patients undergo routine laryngeal exam after surgery compared to laryngoscopy performed only in patients with persistent and severe voice changes 1

Management

Conservative Management

• Most unilateral RLN injuries show compensation from the opposite vocal cord over time 3
• For transient voice alterations (usually recovering within 1-3 days), administering steroids to reduce swelling and inflammation and providing neurotrophic drugs can be considered 1
• In the majority of cases, recovery occurs within 1-3 months 1

Surgical Interventions

• For persistent dysphagia, interventions such as thyroplasty or vocal cord injections may be considered 3
• Treatment options include Teflon injection, medialization thyroplasty, arytenoid adduction procedures, or reinnervation by nerve transfer 2
• In cases of significant aspiration risk, a tracheostomy may be considered to protect the airway 3

Prevention Strategies

• Capsular dissection, visual identification, and intraoperative nerve monitoring can reduce the definitive RLN injury rate to 0.3-3% and transient forms to 6-8% 1
• Left-sided approach in anterior cervical spine surgery reduces the incidence of postoperative and permanent RLNP significantly 6
• Endotracheal cuff pressure reduction used additionally decreases the rate of RLNP even more 6

Risk Factors and Special Considerations

• Re-operative procedures carry a significantly higher risk of RLN injury (up to 30%) 3
• Active smoking and thoracoscopic surgery (vs. robotic surgery) are independent unfavorable predictors for recovery from palsy 4
• The incidence of RLNP is relatively high in the 7th and 8th decades and is twice as high in male patients as in female patients 7

Prognosis

• Permanent vocal cord paralysis is exceedingly rare, with rates ranging from 0.04% to 0.17% 1
• Recovery rates vary depending on the cause, with only about 25% of patients recovering from left RLN palsy after esophagectomy 4
• Patients with persistent unilateral RLNP require appropriate treatment for hoarseness, regardless of its cause 7