LARYNGEAL PARALYSIS

LARYNGEAL PARALYSIS

1. Superior laryngeal nerve (SLN)
2. Recurrent laryngeal nerve (RLN)

1. Brainstem Nuclei
2. Corticobulbar fibers start from the cerebral cortex and descend through the internal capsule and synapse at the nucleus ambiguus in the Medulla
3. Vagus Nerve

RECURRENT LARYNGEAL NERVE (ABDUCTOR) PARALYSIS

• Recurrent laryngeal nerve injury is the most common cause of vocal cord paralysis.
• Supplies all the muscles (posterior Cricoarytenoid, interarytenoid, lateral Cricoarytenoid, and Thyroarytenoid muscles) except for Cricothyroid.
• The recurrent laryngeal nerve runs with the inferior thyroid artery toward the lower lobes of the thyroid.
• This means that the recurrent laryngeal nerve would be at risk in any surgery involving the inferior thyroid artery or the inferior poles of the thyroid.
• Vocal cord palsy in thyroid surgery is due to injury to Recurrent Laryngeal  nerve.
• Lt RLN.: Arises from vagus in the mediastinum at the level of arch of aorta loops around it and then ascends into the neck
• Rt. RLN: Arises from vagus at the level of subclavian artery, hooks around it and then ascends up.

• More common on left side than right side because of the longer and more convoluted course of the left recurrent laryngeal nerve (Rt side is involved only in 3-30% cases) 
• Most unilateral vocal cord paralysis are secondary to surgery
• Ipsilateral paralysis of all muscles except Cricothyroid
• Vocal cord assumes median or paramedian position does not move laterally during inspiration
• Semon’s law: in all organic lesions abductor fibers are more susceptible and paralyzed earlier than the adductors
• Wagner and Grossman hypothesis: Cricothyroid receives innervations from SLN, keeps the vocal cord in paramedian position.
• One third patients asymptomatic,while others may have some voice change
• Small change in voice
• Voice gradually improves due to compensation by healthy cord which crosses midline to meet the paralyzed one
• No aspiration, airway obstruction, no treatment required

2. BILATERAL RLN PARALYSIS

• Most dangerous lesion of vocal cords is bilateral abductor paralysis (Bilateral RLN palsy).
• This is because recurrent laryngeal nerve palsy will lead to paralysis of all laryngeal muscles except the cricothyroid muscle (as it is supplied by superior laryngeal nerve).
• The cricothyroid muscle is an adductor & therefore this will leave both the cords in median or paramedian position thus endangering proper airway, leading to stridor and dyspnoea.
• Trauma due to thyroidectomy is the most common causes.All intrinsic muscles paralyzed, vocal cord in median or paramedian position due to unopposed action of Cricothyroid
  • Bilateral Recurrent laryngeal nerve injury may lead to respiratory distress after Thyroid Surgery.
• Airway obstruction – dyspnea, stridor
• Voice is normal
• Treatment — most cases require tracheostomy as emergency procedure
• Lateralization of cord — done by various procedures
  • Arytenoidectomy
  • Endoscopic lateralization
  • Type II thyroplasty
  • Kashima operation: Cordectomy

CAUSES OF RECURRENT LARYNGEAL NERVE PARALYSIS

Right

• Neck trauma
• Aneurysm of subclavian artery
• Carcinoma right lung apex
• Tuberculosis of cervical pleura

Left

• Trauma
• Bronchogenic cancer
• Ca thoracic esophagus
• Aortic aneurysm
• Mediastinal lymphadenopathy
• Enlarged left auricle
• Intrathoracic surgery

Both

• Thyroid surgery:Most common cause.
• Thyroid carcinoma(Laryngeal carcinoma especially glottic can cause U/L or B/L Vocal Cord paralysis )
• Ca cervical esophagus
• Cervical lymphadenopathy
• Idiopathic

PARALYSIS OF SUPERIOR LARYNGEAL NERVE

 1. UNILATERAL PARALYSIS OF SUPERIOR LARYNGEAL NERVE

• Paralysis of cricothyroid muscle and ipsilateral anesthesia of larynx above the vocal cord
• Voice is weak and pitch cannot be raised.
• Loss of timbre of voice.
• Askew position of glottis as anterior commissure is rotated to the healthy side
• Shortening of cord with loss of tension.
• Paralyzed cord appears wavy due to lack of tension
• Flapping of paralyzed cord — sags down during inspiration and bulges up during expiration

2. BILATERAL PARALYSIS OF SUPERIOR LARYNGEAL NERVE

• Both cricothyroid muscles are paralyzed along with anesthesia of upper larynx
• Paralysis and anesthesia causes inhalation of food and pharyngeal secretions giving rise to cough and choking fits
• Voice is weak and husky
• Treatment:Epiglottopexy — reversible procedure to close laryngeal inlet to protect lungs from repeated aspiration

COMBINED PARALYSIS OF RLN & SLN

• Peripheral neuritis causes high vagal palsy which leads to both superior as well as recurrent laryngeal nerve palsy i.e. bilateral complete palsy. 

1. UNILATERAL PARALYSIS OF RLN AND SLN

• Paralysis of all muscles on one side except interarytenoid as it receives supply from the opposite side also
• Thyroid surgery is the most common cause.
• Recurrent laryngeal nerve palsy and External branch of superior laryngeal nerve palsy may occur as a complication of hemithyroidectomy surgery.
• Vocal cord lies in cadaveric position, 3.5mm from midline
• Healthy cord is unable to approximate the paralyzed cord
• Hoarseness, aspiration, ineffective cough due to air waste
• Treatment: Type I thyroplasty, injection of Teflon paste to paralyzed cord, arthrodesis of cricoarytenoid joint

2. BILATERAL PARALYSIS OF RLN AND SLN

• All laryngeal muscles are paralyzed and there is total anesthesia of larynx
• Both cords lie in cadaveric position
• Aphonia, aspiration and inability to cough
• Treatment: Tracheostomy, epiglottopexy, vocal cord plication, total laryngectomy

POSITION OF VOCAL CORDS

Position of cord	Location from midline	Defect
Median	midline	RLN palsy
Paramedian	1.5 mm	RLN palsy
Intermediate(Cadaveric)	3.5 mm	Both RLN and superior laryngeal nerve palsy
Gentle abduction	7.5mm	ADDUCTOR PALSY

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