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.
Congenital 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
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.