Laryngeal paralysis: The inspiration and the aspiration

Katy Fryer, DVM, DACVS
Veterinary Specialty Hospital, San Diego, CA
Posted on 2016-08-16
 

Laryngeal paralysis is one of the more common upper respiratory emergencies seen in our aging canine population. It is frequently diagnosed in the spring to summer time as the weather begins to warm and we are more active with our canine companions. Clinical signs of this disease can be relatively harmless, such as a change in bark, occasional regurgitation, or intolerance of activity, and are often written off by our clients as normal aging changes. Conversely, dogs can also be presented with life-threatening respiratory distress, hyperthermia, and collapse.

Laryngeal paralysis results from a failure of the cricoarytenoideus dorsalis muscle to contract appropriately during the inspiratory phase of the respiration, causing the arytenoid cartilages and the vocal folds to remain in a paramedian position obstructing laryngeal airflow. When discussing this process with clients, I often liken the arytenoid cartilages to curtains which are supposed to be drawn open and out of the airway during inhalation to allow airflow into the lungs. With laryngeal paralysis it is as if someone has cut the drawstring to our curtains and they can no longer be opened, instead remaining in the center of the airway impeding air movement.

Hereditary forms of laryngeal paralysis have been reported in Bouviers des Flandres, Dalmatians, Rottweilers, Siberian Huskies, white-coated German Shepherd Dogs, Bull Terriers, Leonberger dogs and Pyrenean Mountain dogs. In these dogs, clinical signs usually manifest themselves at a fairly young age. The prognosis for hereditary laryngeal paralysis is considered to be poor with most dogs dying or being euthanized by two years of age.

Idiopathic disease is diagnosed in up to 89% of cases of laryngeal paralysis. The median age at presentation is 11 years, with male dogs being 1.5 times more frequently affected than females. Large and giant breed dogs are over-represented, with Labradors, Chesapeakes, Great Danes, Irish Setters, and Afghan Hounds being the most often affected.

Complete workup of patients before interventions should be performed. This should include thoracic auscultation to evaluate for evidence of pneumonia or pulmonary edema, a complete neurologic exam to evaluate for polyneuropathies which may be associated with myasthenia gravis or hypothyroidism, and thoracic radiographs to evaluate for megaesophagus and the presence of a compressive mediastinal mass. CBC and chemistry profile are also recommended, although they often are unremarkable.

Definitive diagnosis of laryngeal paralysis is most often achieved by performing oral laryngoscopy. A light plane of anesthesia is required for evaluation, with single agent anesthetic protocols of either thiopental or propofol yielding the fewest false positives. Doxapram may be used at a dose of 1mg/kg to augment ventilatory efforts. It is important to differentiate paradoxical motion from true motion during laryngeal evaluation. Alternative means of diagnosis include echo laryngography and transnasal laryngoscopy which may be performed with minimal to no sedation.

Conservative treatment of laryngeal paralysis should include weight loss, avoiding situations of stress, excitement, and increased ambient temperatures, sedatives, and occasionally steroids to decrease inflammation. Surgery is considered the most effective means of treating and palliating the signs associated with laryngeal paralysis. Surgery is contraindicated if concurrent megaesophagus is observed.

The primary goals of surgical treatment are to enlarge the airway, decrease resistance to inspiratory airflow and to maintain resistance during expiration. Though many different surgical techniques have been performed, arytenoid lateralization is considered the gold standard of treatment. In small animals, lateralization methods have evolved by borrowing from equine surgical techniques. Generally, a left lateral approach to the arytenoid cartilage is performed, and one or two sutures of 2-0 polypropylene on a tapered needle are used to secure the muscular process of the arytenoid cartilage to the caudodorsal cricoid cartilage. Intraoperative laryngeal examination is recommended to ensure appropriate abduction as it may reduce the incidence of post-operative complications.

With surgery, reported mortality ranges from 0% to as high as 67% if a bilateral lateralization is performed. Aspiration pneumonia is the most frequently reported complication occurring in somewhere between 8-21% of dogs. Aspiration pneumonia remains a lifelong risk for dogs undergoing lateralization although it appears that dogs may undergo an adjustment period following surgery ultimately making them less likely to develop pneumonia as the time from surgery increases. Minor complications reported to be associated with surgery include coughing, gagging, seroma formation, vomiting, and continued exercise intolerance.

Though it is known to be associated with a polyneuropathy and is most frequently seen in our geriatric dog population, laryngeal paralysis can be successfully managed or treated surgically. Overall, up to 90% of surgical outcomes have been reported satisfactory by owner perception, with most animals achieving resolution of respiratory signs.
 

Featured image above by sgilsdorf (Flickr) , via Wikimedia Commons