Vocal Cord Paralysis

Nerve supply of the laryngeal muscles All the intrinsic muscles of the larynx, with the exception of the cricothyroids, are supplied by the recurrent laryngeal nerves. The cricothyroids, which act as tensors of the cords, are supplied by external branches of the superior laryngeal nerves. Semon’s law In a progressive lesion of the recurrent laryngeal nerves, the abductors are paralysed before the adductors.Thus, in incomplete paralysis, the cord will be brought to the midline by the adductors, but in complete paralysis it falls away to the paramedian position. Semon’s law is not fully understood, but may reflect the fact that the adductor muscles are much more powerful than the abductors. Recurrent laryngeal nerve palsy (Figs 36.1 and 36.2) The left recurrent laryngeal nerve has a long course, extending down into the chest before recurring around the arch of the aorta to return to the larynx. It is therefore more susceptible to disease than the shorter right recurrent nerve, which turns around the subclavian artery. The voice in recurrent nerve palsy is weak and breathy, and the cough is ineffective. As compensation by the opposite cord occurs, the voice improves. The causes of left recurrent nerve palsy in the chest are: 1 carcinoma of the bronchus; 2 carcinoma of the oesophagus; 3 malignant mediastinal nodes; 4 aortic aneurysm; 5 cardiac and oesophageal surgery. The causes of paralysis of the right or left recurrent nerve in the neck are: 1 thyroid surgery; 2 carcinoma of the thyroid gland; 3 carcinoma of the hypopharynx and oesophagus; 4 cervical spine surgery (Cloward’s operation); 5 penetrating wounds; 6 mediastinoscopy. Some cases of recurrent nerve palsy are idiopathic or may follow viral infections, such as influenza. Bilateral recurrent laryngeal nerve palsy Bilateral recurrent laryngeal nerve palsy occurs most commonly following surgery or malignancy of the thyroid gland, but may be the result of pseudobulbar palsy. Because the cords lie near the midline, the airway is impaired and tracheostomy may be necessary. Combined vagal and recurrent nerve palsy Combined vagal and recurrent nerve palsy occurs in lesions of the medulla or vagus trunk. 1 Medulla—neoplasm, vascular lesions, syringobulbia, bulbar poliomyelitis. 2 Vagus trunk—tumours of the skull base, e.g. carcinoma of the nasopharynx; tumours of the jugular foramen—glomus jugulare tumour; chemodectoma of the vagus. Functional aphonia Functional aphonia is a condition found mostly in teenaged females and is psychogenic. The voice is reduced to a whisper, examination shows weak adduction of the cords but sound is produced normally on coughing.Treatment lies in the realm of the communication therapist or psychotherapy. Treatment of vocal cord paralysis The first step is always to try to identify the cause. Bilateral cord palsy will probably produce stridor and urgent tracheostomy may be required. The airway can be improved by arytenoidectomy, but the voice will be worse as a result. The voice can be improved in cases of unilateral cord palsy by the endoscopic injection of a suspension of microspheres of inert plastic material alongside the paralysed cord.This will move the paralysed cord medially and allow the opposite cord to meet its fellow. Improvement in voice quality results. It will also restore laryngeal competence and improve the ability to cough effectively. It is a very good palliation in cases of carcinoma of the bronchus. For unilateral vocal cord palsy of a cause compatible with survival, the operation of vocal cord medialization is available. A window is cut in the thyroid cartilage and a block of silastic inserted to displace the cord towards the mid line. It has the advantage of being reversible if the cord palsy should recover. Functional aphonia is usually self-limiting, or responds to explanation and encouragement. The help of the speech therapist is valuable in persistent cases and some patients may require psychiatric treatment.

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