Megaesophagus is a relatively common condition in dogs that affects the vital tube that moves food from the mouth into the stomach: the esophagus. Though its digestive system location may lead you to assume we're dealing with a gastrointestinal disease, the truth is more complicated than that.
That's because megaesophagus tends to occur as a result of nerves that don't properly function to move food down to the stomach after it's been swallowed. Instead, the nervous system's localized failings leads foodstuff to ball up in the esophagus and get regurgitated back towards the mouth at some point. The enlargement of the esophagus that happens with slackening smooth muscles and stretching from food accumulation results in "megaesophagus."
The problem with megaesophagus is not only that food doesn't end up serving its nutritional purpose but, more dangerously, that food moving in the wrong direction can enter the trachea and the lungs as it does so. Consequently, aspiration pneumonia is the most common reason dogs succumb to this disease.
Dogs with megaesophagus are usually divided into two groups: Those with congenital megaesophagus (which typically shows up in the first weeks to months of life) and those with the acquired form (which is typically encountered by older dogs).
Congenital megaesophagus is usually the result of incomplete development of the nervous system or due to a physical obstruction of the esophagus caused by a remnant of a fetal vessel (persistent right aortic arch).
Acquired megaesophagus is often the result of specific nervous system diseases (such as myasthenia gravis and Addison's disease), though a variety of other conditions have been associated with it (hypothyroidism and laryngeal paralysis, in particular). Obstructions to the esophagus (as with a foreign body) can also cause an enlarged, stretched esophagus, though these cases are typically considered separately from the disease we call megaesophagus.
Unfortunately, most cases of megaesophagus have no known cause. These dogs are referred to as having the "idiopathic" form of the disease.
Symptoms and Identification
The typical symptom of megaesophagus is regurgitation. Dogs will bring up undigested food with no abdominal effort (as opposed to what we observe with vomiting, where dogs will throw up partially digested food while making significant abdominal movements).
Should aspiration pneumonia ensue (as is very common), dogs will cough, become lethargic and suffer fevers. The typical megaesophagus patient will be identified through his symptoms along with simple X-rays. X-rays of the chest will reveal a distension of the esophagus and may demonstrate aspiration pneumonia as well.
The hard part of diagnosing megaesophagus is not identifying the disease process itself, but determining its underlying cause (if one can be identified). Blood tests for specific nervous system diseases that cause megaesophagus, endoscopy to visually investigate the esophagus and biopsy the affected tissue, and sometimes provocative medical treatment (to attempt to isolate the cause by treating for it) are the most common approaches to this condition.
For the congenital form, the following breeds are predisposed:
In the acquired version, the breed predisposition varies according to the different disease processes that underlie the megaesophagus. However, the following breeds seem predisposed:
Treatment of megaesophagus is typically relegated to symptomatic approaches. Although some can be treated directly with medications and surgical approaches that can correct the underlying disease process, most patients will continue to experience long-term symptoms from the unfortunate stretching of and permanent nerve damage to such a vital structure.
Because food will continue to accumulate in the esophagus for most patients (to varying degrees) and because aspiration pneumonia will therefore remain a significant risk, several strategies to control the regurgitation of food are typically employed:
feeding from a height to facilitate downward movement of food
feeding a slurry instead of firm, wet food or crunchy kibble
maintaining elevation of the body after eating
esophageal tube feeding or surgical stomach tube placement
Diagnosis of the basic condition is typically not expensive, per se. Identifying the underlying cause and treating it, however, may prove expensive--prohibitively so for pups with a persistent right aortic arch, for example.
Furthermore, the long-term nature of symptoms in most cases not only requires significant dedication of time and effort on the part of owners, it also means that bouts of life-threatening aspiration pneumonia may periodically ensue. The expense of this latter possibility will often prove insurmountable for owners whose pets require ICU-style care (up to $1,000 a day) during these critical periods.
Preventing megaesophagus comes down to removing affected individuals from breeding programs, regardless of the cause of the disease. Their siblings and parents should also be tested for the disease underlying the megaesophagus before they are allowed to continue or enter breeding programs.
Gaynor AR, Shofer FS, Washabau RJ. Risk factors for acquired megaesophagus in dogs. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104-6010, USA.
Shelton GD, Schule A, Kass PH. Risk factors for acquired myasthenia gravis in dogs: 1,154 cases (1991-1995). Department of Pathology, School of Medicine, University of California-San Diego, La Jolla 92093-0612, USA.