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 function is not normal.

The cricoarytenoideus dorsalis muscle abducts the arytenoid cartilages at each inspiration. The laryngeal recurrent nerve innervates this muscle. Lesions to the laryngeal recurrent nerve or to the cricoarytenoideus dorsalis 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. Wallerian degeneration of the laryngeal recurrent nerves and abnormalities of the nucleus ambiguus are both present. Dogs with congenital laryngeal paralysis are clinical at an early age (before one year old) than dogs with acquired laryngeal paralysis.

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. Diseases and conditions may contribute to laryngeal paralysis. A cranial mediastinal or neck mass stretching or compressing the laryngeal recurrent nerve can induce a laryngeal paralysis. Trauma to the laryngeal recurrent nerve during dogfights or during surgery in the neck is a cause of laryngeal paralysis. Laryngeal paralysis in the cat has been diagnosed after bilateral thyroidectomy. Finally, neuropathy involving the laryngeal recurrent nerve or myopathy involving the intrinsic muscle of the larynx, and endocrine insufficiency (hypothyroidism) that can induce a polyneuropathy or a polymyopathy are other causes of laryngeal paralysis in the adult dog.

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 dyspnea, cyanosis, or syncope occur in severely affected patients. Male dogs are approximately 3 times more affected than female. Laryngeal paralysis can be accompanied with various degrees of dysphagia which significantly enhances the probability of aspiration after surgical correction of the laryngeal paralysis.

Physical Examination

The physical examination of dogs with laryngeal paralysis is fairly unremarkable. Dogs have an inspiratory dyspnea that is not alleviated with open mouth breathing. Mild lateral compression of the larynx significantly increases inspiratory dyspnea. 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 neurologic 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.

Radiographic Examination

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. 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.