Managing laryngeal paralysis (Proceedings)
The laryngeal functions are to regulate airflow, voice production, and prevent inhalation of food. If the intrinsic muscles and/or the nerve supply of the larynx are not normal laryngeal functions are compromised.
The dorsal cricoarytenoide muscle abducts the arytenoid cartilages at each inspiration. The laryngeal recurrent nerve innervates this muscle. Central lesions or lesions to the laryngeal recurrent nerve or to the dorsal cricoarytenoide muscle result in laryngeal paralysis in dogs and cats. Laryngeal paralysis can be unilateral or bilateral
EtiologyCongenital and acquired forms of laryngeal paralysis have been recognized in dogs and cats.
Congenital laryngeal paralysis
Congenital laryngeal paralysis has been reported in Bouvier des Flandres, bull terrier, Dalmatian, Rottweiller and Huskies. Bouvier des Flandres and bull terrier have mostly been reported from Europe while the Dalmatian and Huskies from United States. Laryngeal paralysis has a hereditary transmission in Bouvier des Flandres with an autosomal dominant trait. Dogs with congenital laryngeal paralysis are clinical at an early age (before one year old) than dogs with acquired laryngeal paralysis. Usually dogs with congenital laryngeal paralysis have several neurological deficits like ataxia.
Acquired laryngeal paralysis
Acquired laryngeal paralysis is most commonly reported in Labrador retriever, Golden retriever, St Bernard and Irish Setter at an age of 9 years old. It has been reported in cats. Acquired laryngeal paralysis is more frequently idiopathic; however, other causes should be ruled out. Several diseases and conditions may contribute to laryngeal paralysis. A cranial mediastinal or neck mass stretching or compressing the laryngeal recurrent nerves can induce a laryngeal paralysis. Trauma to the laryngeal recurrent nerve during dogfights or during surgery in the neck can cause of laryngeal paralysis. Laryngeal paralysis in the cat has been diagnosed after bilateral thyroidectomy. Finally, a ployneuropathy involving the laryngeal recurrent nerve is the most common cause of laryngeal paralysis. The polyneuropathy can be due to an endocrine insufficiency (hypthyroidism). However most of the time a diagnosis of idiopathic polyneuropathy is made because no causes can be identified. A myopathy involving the intrinsic muscle of the larynx.
The presenting signs are similar for the congenital and acquired forms. Progression of signs is often slow; months to years may pass before an animal develops severe respiratory distress. Early signs include change in voice, followed by gagging and coughing, especially during eating or drinking. Endurance decreases and laryngeal stridor (especially inspiratory) increases as the airway occlusion worsens. Episodes of severe difficulty breathing, cyanosis, or syncope occur in severely affected patients. Male dogs are approximately three times more affected than female. Laryngeal paralysis can be accompanied with various degrees of dysphagia, which significantly enhances the probability of aspiration pneumonia after surgical correction of the laryngeal paralysis.
The physical examination of dogs with laryngeal paralysis is fairly unremarkable. Dogs have a difficulty breathing on inspiration that is not alleviated with open mouth breathing. Mild lateral compression of the larynx significantly increases inspiratory effort. Referred upper airway sounds are present during auscultation of the thoracic cavity. Auscultation of the thoracic cavity and the lung field may reveal the presence of pneumonia in the cranial lung lobe due to aspiration. Palpation of the muscle mass may reveal skeletal muscle atrophy in cases of polyneuropathy. The tibial cranial muscle is very commonly atrophied in dogs with endocrine polyneuropathy. A complete neurological examination is required to evaluate the animal for a polyneuropathy.
Complete blood count and chemistry profile are usually within normal limits. Hypercholesterolemia, hyperlipidemia, and augmentation of liver enzymes activity are present on the chemistry profile for dogs with hypothyroidism. A thyroid profile with endogenous TSH and free T4 is then required to further define the diagnosis. Laryngeal paralysis has inconsistent correlation with hypothyroidism.
It is necessary to perform a radiographic examination of the thoracic cavity for the evaluation of the lung parenchyma and the esophagus. Aspiration pneumonia is common finding pre-operatively in dogs with laryngeal paralysis. If aspiration pneumonia is present the surgical intervention should be delayed until the aspiration pneumonia resolved. Pulmonary edema is not uncommon in dogs with an acute exacerbation of their clinical signs. Pulmonary edema needs to be treated aggressively and the surgery for the laryngeal paralysis does not need to be delayed. Megaesophagus might be present in dogs with laryngeal paralysis especially if the paralysis is due to polyneuropathy or polymyopathy. Megaesophagus places the animal at more risk for aspiration pneumonia after surgery. Radiographic examination of the larynx is unremarkable.
A laryngeal examination under general anesthesia is required for the diagnosis of laryngeal paralysis. A light plane of anesthesia is required to be able to evaluate the laryngeal function during each inspiration. Thiopental or propofol is used intravenously as needed for the anesthesia. The animal should be anesthetized to the point at which the mouth can be opened easily and a laryngeal reflex is still present. If the animal is too deeply anesthetized the larynx looks paralyzed even in the normal animal. If the plane is too deep it is important to let the animal approach consciousness and examine the laryngeal function during this time. During the laryngeal examination, motion of the arytenoid cartilage is observed during inspiration. Dopram intravenously can be used to stimulate the central respiratory center and have a better laryngeal examination. The animal should be placed in sternal recumbency and the head elevated to the level that it is normally carried. In the normal animal the vocal fold and the arytenoids should abduct during inspiration and passively relax during expiration. The arytenoid cartilages and the vocal cords are immobile and drawn toward midline during inspiration if the animal has laryngeal paralysis. If the paralysis is unilateral only one cartilage is not moving. Edema and erythema of the mucosa of the arytenoid cartilages is present on the dorsal part of the larynx and appear to be due to repeat trauma of the arytenoid touching each other at each inspiration. Paradoxical motion of the arytenoid can be present and makes the diagnosis more difficult. With paradoxical motion the arytenoid cartilages are sucked in the airway during inspiration and are moving back to a normal position during expiration. This gives the impression the patient does not have laryngeal paralysis.