Laryngeal Paralysis

Hypocalcemia following total or subtotal thyroidectomy where all four parathyroid glands are either removed results due to parathyroid insufficiency.

Parathyroid insufficiency (hypocalcemia) is usually not seen after Hemithyroidectomy as it involves the removal of only one lobe of thyroid together with the isthmus and the parathyroids are preserved.

In patients having bilateral paralysis of recurrent laryngeal nerve, the airway is inadequate since both the cords lie in the median and paramedian position causing dyspnoea and stridor but the voice is preserved.

In bilateral recurrent and superior laryngeal nerve palsy all the laryngeal muscles are paralysed and both cords lie in the cadaveric position i.e 3.5mm from the midline. There is also total anaesthesia of the larynx.

• In bilateral recurrent laryngeal nerve palsy, vocal cords lie in median or paramedian position due to unapposed action of cricothyroid muscles. 
• In unilateral paralysis of superior laryngeal nerve, there is shortening of the cord with loss of tension. The paralysed cord appears wavy due to lack of tension.

Recurrent laryngeal nerve injury is the most common cause of vocal cord paralysis. It from the Vagus, travels further on the left where it loops around the arch of Aorta while on the right, it travels around the subclavian artery. Supplies all the muscles (posterior Cricoarytenoid, interarytenoid, lateral Cricoarytenoid, and Thyroarytenoid muscles) except for Cricothyroid.

• Brainstem Nuclei
• Corticobulbar fibers start from the cerebral cortex and descend through the internal capsule and synapse at the nucleus ambiguus in the Medulla
• Vagus Nerve
• Recurrent Laryngeal Nerve is the commonest cause.

• Thyroarytenoideus internus (vocalis) – adductor and major tensor of free edge of vocal fold.
• Thyroarytenoideus externus – major adductor of vocal fold
• Thyroepiglotticus – shortens vocal ligaments

 Anesthesia of larynx

Ans. is ‘a’ i.e. Recurrent laryngeal nerve palsy

The nerves found in close relationship to thyroid gland and therefore likely to be involved in malignant spread and thyroid surgery are – recurrent laryngeal nerve and – superior laryngeal nerve.

Ans. is ‘a’ i.e. Hypocalcemia 

“Transient or permanent hypocalcemia is very unlikely after hemithyroidectomy, since the opposite lobe is not

disturbed.”- Endocrine surgery by Arthur E. Schwartz

Hypocalcemia is seen after total or subtotal thyroidectomy d/t inadvertent removal of parathyroid glands or their injury during surgery.

Ans. is ‘a’ i.e. hypocalcemia 

• Though hypocalcemia can cause stridor d/t laryngeal spasm, it is seen 2-5 days after operation. Bailey and Love write -“Most cases present dramatically 2-5 days after operation but, very rarely, the onset is delayed for 2-3 weeks or a patient with marked hypocalcemia is asymptomatic.”
• One shoudn’t be confused with laryngomalacia. This is not congenital laryngomalacia which occurs in the newborn. This laryngomalacia is softening of the larynx and trachea due to continuous pressure on it by a large goitre. Removal of the goitre causes collapse and kinking of the larynx and trachea leading to airway obstruction.

Ans is None 

• All the given conditions are able to cause resp. distress.
• Endocrine surgery of Head & Neck writes
• “The reason for airway compromise include :

bilateral recurrent laryngeal nerve injury

tracheal malacia from longstanding tracheal compression caused by a large thyroid mass

subglottic edema from laryngeal involvement with tumor,

tracheal invasion by tumor

post-op hemorrhage or hematoma.”

Hypocalcemia can also cause stridor by causing laryngeal spasm 

Ans. is ‘b’ i.e., Recurrent laryngeal nerve 

Ans. is ‘c’ i.e., Left recurrent laryngeal nerve

All muscles which move the vocal cord (abductors, adductors or tensors) are supplied by the recurrent laryngeal nerve except the cricothyroid muscle which is supplied by external laryngeal nerve (a branch of superior 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.

So, any mediastinal causes viz mediastinal lymphadenopathy and aortic aneurysm would parlyse Lt. RLN. only

Vocal nodule does not cause vocal cord palsy.

Laryngeal carcinoma especially glottic can cause U/L or B/L Vocal Cord paralysis – Conn’s Current Theory

Causes of bilateral recurrent laryngeal nerve palsy are:

• Idiopathic
• Post thyroid surgery
• Thyroid malignancy
• Carcinoma of cervical part of esophagus
• Cervical Lymphadenopathy

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

Ans. is b i.e. bilateral abductor 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.

Ans. is c i.e. Preservation of speech with severe stridor and dyspnea

Ans. is d i.e. normal or good voice

Management

• Lateralization of cord by arytenoidectomy, endoscopic surgery, thyroplasty type II, cordectomy
• In emergency cases -Tracheostomy may be required

Also know

• Generally patients with bilateral recurrent laryngeal nerve palsy have a recent history of thyroid surgery or rarely an advanced malignant thyroid tumor.
• Most common presentation-Development of stridor following URI
• Since the voice of the patient is normal\it is diagnosed very late.

Ans. is d e. Loss of timbre of voice

Paralysis of Superior Laryngeal Nerve -causes paralysis of cricothyroid muscle which is a tensor of vocal cord.

Clinical Features

• Voice is weak and pitch cannot be raised.
• U/L Anaesthesia of larynx above the level of vocal cords causing occasional aspiration.

Ans. is a i.e. Common in (left) side

Unilateral Recurrent Laryngeal Nerve Palsy

• 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) (i.e. option a is correct)
• Most unilateral vocal cord paralysis are secondary to surgery (i.e. option b is incorrect)
• Unilateral injury to recurrent laryngeal nerve leads to ipsilateral paralysis of all intrinsic muscles except cricothyroid (which is an adductor of vocal cord). The vocal cord thus assumes a median or paramedian position which does not move laterally on deep inspiration (i.e. option c is incorrect)

Clinical Features

• Asymptomatic in 1 /3^rdcases
• In rest of the patients there may be some voice problem i.e. Dysphonia – the voice is hoarse & becomes weak with use. This gradually improves with time due to compensation by the healthy cord which crosses the midline to meet the paralysed one. Generally no speech therapy is required (i.e. option d is incorrect).

In U/L abductor palsy, the affected vocal cord assumes a median or paramedian position. The other is normal so one third patients are asymptomatic while others may have some voice change.

Recurrent Laryngeal Nerve paralysis:

If both recurrent laryngeal nerves are interrupted, the vocal cords lie in a cadaveric position in between abduction and adduction and phonation is completely lost.

When only one recurrent laryngeal nerve is affected, the opposite vocal cord compensates for it and phonation is possible but there is hoarseness of voice

Superior Laryngeal Nerve paralysis

It divides into external and internal laryngeal nerves. External laryngeal nerve supplies cricothyroid and inferior constrictor and internal laryngeal nerve supplies mucous membrane of the larynx upto the level of vocal folds:

• Asymmetric vocal cord tension
• Produces diplophonia
• Loss of vocal fold tension (lowers pitch of voice)
• Inaccurate vocal cord apposition
• Paralysed side slightly shortened and bowed
• May be depressed below level of normal side
• Rotation of AP axis of vocal cords
• Posterior commissure points to side of paralysis
• Loss of laryngeal sensation and increased risk of aspiration