Laryngeal Paralysis in Dogs: 5 things we've learned in the past decade

Laryngeal paralysis is a functional disorder of the larynx resulting in decreased abduction of the arytenoid cartilages during inspiration in dogs and cats. This causes airway obstruction, dyspnea and in some cases life threatening hypoxia. Clinical studies of various aspects of the disorder have improved our understanding of laryngeal paralysis. Key elements of some of these studies are listed and briefly described below.

Esophageal Dysfunction

Barium swallow in a dog with significant esophageal pathology

Idiopathic laryngeal paralysis is a disorder affecting more than just the larynx. Studies have conclusively shown that esophageal motility is abnormal in dogs with laryngeal paralysis.(1) This is a significant finding for many reasons, not the least of which is the relationship of esophageal dysfunction with aspiration pneumonia that commonly occurs after surgical correction by arytenoid lateralization. Dogs with esophageal or gastric disorders that predispose them to regurgitation can increase their chance of aspirating and developing pneumonia postoperatively.

When evaluating dogs with laryngeal paralysis, be sure to get a complete history with emphasis on the animal’s ability to prehend food and swallow normally.  Inquire about any regurgitation and vomiting. Obtain thoracic radiographs to evaluate for aspiration pneumonia and megaesophagus. If the dog appears to be a significant risk for aspiration, consider permanent tracheostomy as an alternative to arytenoid lateralization to reduce the risk of pneumonia. Metoclopramide can be administered to laryngeal paralysis dogs as a premedication to reduce the risk of regurgitation during general anesthesia. 

Polyneuropathy

More evidence that laryngeal paralysis is a complicated disorder affecting multiple organ systems are the studies showing its association with peripheral neuropathy.(2,3)  Several clinical investigations have documented generalized neuropathy in dogs that have laryngeal paralysis, emphasizing the need to thoroughly evaluate the neurologic status of these animals. Owners should be educated about this association, particularly in dogs that are not obviously affected by neuropathy when first presenting for their upper airway obstruction. Clinical signs of neurologic deficits may become evident sometime after treatment of the laryngeal paralysis.

Doxapram

An essential part of the diagnosis of laryngeal paralysis is the sedated laryngeal exam. Laryngeal function is assessed by watching the arytenoid cartilages abduct during inspiration. Since laryngeal function may be affected by the sedative drugs administered for the examination, a false positive result can occur if the sedation is excessive. Erratic respirations can also occur, complicating the assessment. Doxapram has been shown to assist in the exam by stimulating respiration allowing a more consistent and accurate evaluation of function.(4) The dosage of doxapram is: 1-5 mg/kg IV.

 Minimal Dissection Lateralization

The original surgical description of arytenoid lateralization included an extensive amount of dissection that is no longer felt to be necessary. After completely disarticulating the crico-arytenoid joint, i.e., the muscular process of the arytenoid from its articulation to the cricoid cartilage, the sesamoid band connecting the arytenoids' corniculate processes was also severed. This was a difficult step in the procedure because of poor exposure and in some cases resulted in perforation of the pharynx. 

Diagrammatic view of sharp incision of the inter-arytenoid sesamoid band.
This step in the surgical procedure is no longer considered necessary by many surgeons.
(reprinted from: Fingland RB. Obstructive Upper Airway Disorders. Saunders Manual of Small Animal Practice, 3rd ed., Birchard and Sherding editors,  Figure 161-6, Elsevier, 2006, pg. 1657)

Satisfactory lateralization is possible by simply incising the joint capsule of the crico-arytenoid articulation and leaving the sesamoid band in tact. Low suture tension has also been shown to be an effective means of opening the rima glottis compared to high suture tension.(5) I have used this “minimal dissection” technique for several years now. It provides for adequate arytenoid abduction, helps to prevent over-correction, and has lessened the incidence of aspiration pneumonia in my experience.

The “Tie-Back” is Not For All Dogs

Although the arytenoid lateralization procedure continues to provide satisfactory treatment for many dogs with laryngeal paralysis, it is contraindicated in dogs that are high risk for aspiration pneumonia. Owners need to realize that the lateralization procedure does not make the larynx normal. It opens the airway and relieves obstruction but the larynx is fixed in its position and not capable of closing. If the epiglottis cannot completely cover the laryngeal opening during swallowing, aspiration is likely to occur. Also, as  discussed previously, esophageal dysfunction or any other cause of chronic regurgitation or vomiting (megaesophagus, gastric disorder, etc.) increases the likelihood of aspiration. In these dogs a permanent tracheostomy should be considered to relieve the airway obstruction. 

A recently performed permanent tracheostomy in a dog.

For details on permanent tracheostomy in dogs, see 
http://drstephenbirchard.blogspot.com/2014/12/permanent-tracheostomy-in-dogs-life.html.

References

1. BJ. Stanley, JG Hauptman, MC Fritz, et. al.

Esophageal Dysfunction in Dogs with Idiopathic Laryngeal Paralysis: A Controlled Cohort Study. Veterinary Surgery Volume 39, Issue 2, pages 139–149.

2. Orla M. Mahony, Kim E. Knowles, Kyle G. Braund, et.al. Laryngeal Paralysis-Polyneuropathy Complex in Young Rottweilers. Journal of Veterinary Internal Medicine Volume 12, Issue 5, pages 330–337.

3. Braund KG, Shores A, Cochrane S, Forrester D, Kwiecien JM, Steiss JE. Laryngeal paralysis-polyneuropathy complex in young Dalmatians. American Journal of Veterinary Research 1994, 55(4):534-542.

4. Tobias KM1, Jackson AM, Harvey RC. Effects of doxapram HCl on laryngeal function of normal dogs and dogs with naturally occurring laryngeal paralysis. Vet Anaesth Analg. 2004 Oct;31(4):258-63.

5. S Bureau, E Monnet. Effects of Suture Tension and Surgical Approach During Unilateral Arytenoid Lateralization on the Rima Glottidis in the Canine Larynx Veterinary Surgery Volume 31, Issue 6, pages 589–595.