Laryngeal paralysis is recognized because of the loss of function in the paired cricoarytenoideus dorsalis (CAD) muscles, which are the only abductors of the arytenoid cartilages. In horses, the condition is usually unilateral (left) and thought to be due to stretching of the left recurrent laryngeal nerve along its longer course around the ligamentum ateriosum. This laryngeal hemiplegia in horses causes stridor that is commonly referred to as roaring and represents more of a performance issue in affected horses than a life-threatening issue.

Laryngeal hemiparesis and hemiplegia probably occur in dogs but are usually not recognized. The clinical entity facing small-animal veterinarians is bilateral laryngeal paralysis. This results in progressively worsening stridor and, ultimately, enough upper airway obstruction that respiratory distress and cyanosis ensue.

Epidemiology

The association between laryngeal paralysis and hypothyroidism is the most tenuous. Dogs may be prone to both diseases without any causality between them, and treatment of hypothyroidism usually does not halt or reverse the progression of laryngeal dysfunction. Many dogs with laryngeal paralysis are euthyroid.

The connections between laryngeal paralysis and other neuromuscular diseases are being increasingly recognized and should prompt a careful history gathering and examination to expose other problems that may be concurrent with the more obvious laryngeal signs.

While laryngeal paralysis is seen as a rare congenital problem in some breeds, the clinically significant variant of this disease is that which typically occurs in geriatric sporting dogs, especially Labrador retrievers. Onset of signs is usually after age 10, and many dogs that require treatment are older (12 to 14 years of age).

In addition to stridor (which is usually audible from a distance or can be heard as a loud machinery sound on laryngeal auscultation), affected dogs may also present with a history of coughing, gagging or choking during swallowing. Exercise intolerance is another frequent sign, and its presence should prompt an investigation as to whether it is simply due to hypoxia or whether it might represent signs of appendicular muscle weakness. When dyspnea occurs, it is usually noted more on inspiration.