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.

Etiology

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.

Clinical findings

History

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.

Physical examination

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.

Laboratory findings

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.