Often referred to as “wheezers,” dogs suffering from laryngeal paresis have an abnormally limited ability to open the larnyx. Laryngeal paralysis and laryngeal paresis are terms that refer to variations of the same condition; paresis means that the larynx is partially paralyzed, while the term paralysis is reserved for dogs who have no ability to open the larynx whatsoever. The larynx is a relatively complicated bit of anatomy that serves as a connection between the mouth, the nose, the esophagus, and the trachea (windpipe). It includes the vocal cords (which are used to generate barks, growls, whines etc). Dogs with laryngeal paresis cannot fully open the arytenoid cartilages, which is a movement that is critical to opening the airway when the dog inhales. If the arytenoid cartilages fail to open, it means that the windpipe remains partially blocked no matter how hard the dog is breathing. Mild cases of laryngeal paresis are usually only evident with the dog is working hard (running, pulling in harness); there is a distinct respiratory stridor, which is probably best described as a honking sound. Because a dog’s ability to dissipate body heat relies largely on panting, the airway restriction also makes these dogs much more susceptible to overheating even when doing relatively easy work in mild weather. Dogs with severe laryngeal paresis or paralysis cannot open their airway wide enough to allow enough air flow to lungs for something as effortless as walking; they will gasp, turn blue, and collapse with very, very minimal efforts. There essentiall two forms of this disease: one is the inherited form (present at birth), and the second is the degenerative form, which comes on in elderly dogs that were normal for most of their lives. The most common form of this disease in sled dogs is the inherited form; it has been documented in Siberian Huskies, Alaskan Huskies, and Husky-pointer hybrids. Severely affected puppies will be obviously abnormal when they are first old enough to walk at about 4 weeks of age; they are often incapable of even walking out of the whelping box without collapsing. Dogs with milder disease will not become evident until they run hard, and the condition is often missed by the owner until the dog starts having trouble perfoming. Specific research on this condition is lacking, but it is believed to be a failure for the recurrent laryngeal nerves to adequately supply full neurological function to the larynx. The recurrent laryngeal nerves (there is a left and right) are another interesting bit of anatomy in that they are one of the longest nerves in the body; they orginate in the brainstem, go down the neck along side the windpipe, go around the first rib, and come all the way back up the neck to the larynx. It is no surprise that a nerve this long is subject to degeneration. In some breeds, most notably elderly Greyhounds and Labrador Retrievers, the nerve deteriorates in function over time and causes a slow, progressive development of laryngeal paresis in geriatric dogs. Almost everyone knows an old Lab that waddles along making a loud, harsh panting sound at a wopping 3 miles an hour; owners are apt to blame this on a “bad heart” or “being out of shape” (which most of them are), but often these wheezing geezers have the degenerative form of laryngeal paresis. While this form of the disease may occur rarely in old sled dogs, the typical sled dog “wheezer” is born with the problem. In Alaskan Huskies, the disease is phenotypically linked to certain color patterns; dogs with blue eyes, ticking, and a broad white mask (“bald”) on their face were often affected or carriers of this trait. Another trait associated with this disease in Alaskan Huskies is called the “wheezer fold,” an abnormal ridge of tissue by the gumline. HOWEVER, not all dogs with these phenotypic traits are wheezers (or carriers for that matter), and not all wheezers have all of these phenotypic traits. Many breeders would try to avoid breeding two dogs with these color patterns together, because the possibility of producing a wheezer was high (both parents had high potential to be asympotmatic carriers of the wheezer trait.) It is worth mentioning that these are phenotypic traits observed in the Alaskan Husky (and nowadays in Alaskan Husky-pointer hybrids), and that pedigree lore, however inaccurate it may be, traces it back to the introduction of a Border Collie into a particular line of dogs decades ago. Please note that there are a bazillion white faced, blue eyed Siberian Huskies around, and that color pattern is NOT correlated with this disease in that breed. Diagnosis of laryngeal paresis/paralysis is done by sedating the patient just heavily enough to observe the larynx working without triggering the normal gagging reflex; the dog will be unable to fully open the vocal folds when she inhales. Since each side of the larynx is supplied by its own nerve (the left or right recurrent laryngeal nerve), the problem is often asymmetrical, so there will be an obvious difference between the left and the right side.Treatment options for this problem are less than ideal, especially when we are considering sled dogs, who are expected to perform at high level of athleticism. The primary treatment available is a surgical procedure called a laryngeal tieback; the surgeon “ties back” the arytenoid cartilage, which serves to keep the airway open all of the time. This comes with a significant complication risk: the ability to close the arytenoid cartilage is one of the movements the larynx makes that allow you to swallow your food safely by preventing it from being pushed down the wind pipe. The tieback procedure fixes the arytenoids in a single position; leaving them too far open runs a high risk of aspiration pneumonia. Dogs that are exercising hard are going to be even more prone to aspiration pneumonia than the average house pet. They run with their mouth wide open, and the risk of saliva, foam, dirt, snow and ice and even dog manure kicked up by their teammates has a greater chance of landing in their airway. Another option is a permanent tracheostomy, but this procedure comes with an even higher risk of aspirating foreign material, even in low activity pet dogs. Ventriculocordectomy may provide mild relief in some cases, but unless properly peformed the dog is at risk for fibrosis (scarring) of the vocal folds, which will make the problem worse.Dogs with confirmed inherited larygneal paralysis or paresis should not be used for breeding. This trait has been selected against by knowledgeable breeders for decades in the sled dog world, and it still crops up occasionally; polluting the gene pool by breeding a wheezer is not an ethical thing to do. Dawn Brown D.V.M. graduated from the New York State College of Veterinary Medicine at Cornell University and practices small animal medicine and surgery at Carthage, New York. She has been racing since 1982, currently 6 and 8-dog limited class speed racing in the lower 48, Canada and Alaska.
Racing in the ACE Race with Tonya Helm On this episode of the Mushing podcast,