Megaesophagus

Megaesophagus is a condition that affects dogs and cats (rare) characterized by a diffused dilation of the esophagus accompanied by a decrease in peristalsis (movement that helps the food travel towards the stomach). Consequently, the animal will regurgitate his food and lose weight as he is not absorbing any of the calories ingested. Moreover, the animal can have frequent complications such as aspiration pneumonia (regurgitated food is aspirated into the lungs) which presents itself with coughing and halitosis (bad breathe) caused by the frequent regurgitation of food.

Megaesophagus can be congenital (present at birth) or acquired later in the life of the animal. An acquired megaesophagus can be obtained after another illness or be idiopathic (of unknown cause). If it is congenital or acquired but idiopathic, it is thought that it could be due to a combination of neurologic malfunction, an alteration of the viscoelasctic properties of the esophagus and a malfunction in the response of the esophageal distention by food. For example, in a case where the megaesophagus is congenital, the motility of the esophagus is weak and this would be caused, in certain patients, by a delay in maturation of the esophageal function that can however improve with time. Myasthenia gravis, a hereditary disease affecting the neuromuscular junctions, constitutes another cause of congenital megaesophagus in certain breeds of dogs. In this case, a general weakness usually accompanies the megaesophagus.

Amongst the dog breeds known for having a greater risk of congenital megaesophagus, there are the Newfoundlands, the Parson Russell terriers, the Samoyeds, the Springer spaniels, the Fox terriers (soft hair), and the Shar-pei. Typically, these dogs will start regurgitating during the weaning process when liquid foods transition to solid. Amongst the Fox terriers that suffer from megaesophagus secondary to myasthenia gravis, the symptoms appear at a younger age (4-9 weeks old).
Other breeds recognized to be affected by the acquired megaesophagus are the Irish setters, the Great Dane, the German shepherd, the Labradors, the miniature Schnauzers as well as the Newfoundlands. Their clinical signs generally appear between 7-15 years of age. In the Newfoundlands affected by myasthenia gravis, the megaesophagus will start appearing before the age of 2 years old.

Cats can also be affected by both the congenital and acquired form of megaesophagus. There is a known breed predisposition in the Siamese.
The exact cause of acquired megaesophagus remains unknown but it is believed that there is a flaw in the transmission of the nervous impulse following the distention of the esophagus. A variety of diseases can affect the esophagus in this way. These include the neuromuscular diseases, immune system diseases, hormonal diseases, gastrointestinal diseases, tumors and toxins.

The definitive diagnosis can be established most of the time by a thoracic radiograph where we can observe a distended esophagus by air or food. It is even possible to visualize the cause of the megaesophagus in the cases where there is a tumor, foreign object, distention/torsion of the stomach or a hiatal hernia (flaw in the diaphragm that permits the abdominal organs to penetrate into the thoracic cavity). When the animal has developed aspiration pneumonia due to his megaesophagus, we can also observe, using a radiograph, the changes that are associated.
In certain circumstances, the dilution of the esophagus can happen after excitation, aerophagia (ingestion of air), a general anesthesia and vomiting.
If a standard radiograph is not enough to confirm the diagnosis, there is need for specialized imagery. For example, we can make the animal swallow barium and then take another radiograph. This opaque, white liquid will then accumulate into the distended esophagus and will facilitate the viewing. We must, however, be cautious with this technique as to prevent the regurgitation and aspiration of the barium into the lungs.
Fluoroscopy is another specialized imagery technique that can be useful even if not necessary to confirm the diagnosis. It essentially constitutes of a radiograph in motion that permits the evaluation of the motility of the pharynx and the intensity of the peristalsis of the esophagus. In a case where there is a decrease of motility, it is more useful to do a fluoroscopy than a barium x-ray.

If we suspect an obstruction of the esophagus or an esophageal reflux, it is possible to insert an endoscope (camera) to have a direct visualization of the foreign body (and remove it if possible), scar tissue or ulcerations caused by gastric acid.
Complementary blood and urine analysis are indicated to try to identify and/or eliminate diseases that could be at the origin of the megaesophagus and treat them.

In the case where megaesophagus is idiopathic, the treatment goal will be primarily to make the animal comfortable, provide a good nutrition and treat the complications. We will have to ensure that the animal’s nutritional needs are met and that regurgitation happens less often. To do this, it is recommended that you offer multiple small meals rich in calories in a vertical position to have the food go down to the stomach with the help of gravity. If the animal is very weak and we cannot control the regurgitations, it might be necessary to insert a tube into the stomach to feed the animal.

The main complications to be worried about is the aspiration pneumonia and the esophagitis (inflammation of the esophagus). In case of pneumonia, antibiotics should be administered based, ideally, on the results of a culture of the secretions of the respiratory tract. In case of esophagitis, a mucus membrane protector will be administered to allow the esophagus to heal and avoid the formation of scar tissue. Antacids will also be added to the treatment to decrease the gastric acidity.
There are medications to increase the motility of the esophagus to help propel the food to the stomach. In case of megaesophagus caused by another disease, treatment with this medication is needed.

The prognostic varies a lot depending on the condition causing the megaesophagus and the health of the animal. For example, if an animal suffers from aspiration pneumonia, of malnutrition and dehydration then his prognostic is not as good. This is also the case for congenital megaesophagus. However, the motility of the esophagus can improve as the animal matures up to 1 years old.

Congenital myasthenia gravis is also associated with a poor prognostic because there is no known specific treatment and aspiration pneumonias are frequent. For this same reason, the prognostic of acquired megaesophagus is poor.
Once the diagnostic is made rapidly, that the condition is treated appropriately, and that the animal does not suffer from severe aspiration pneumonia or of thymoma (tumor of the thymus), the prognostic of acquired myasthenia gravis can be favorable. It happens, at times, that in average after 6 months, there is spontaneous remission of the myasthenia gravis and disappearance of the megaesophagus. However, there are still many dogs that die of aspiration pneumonia during the first month after diagnostic.

In general, neuromuscular diseases have a poor prognostic. As with many other diseases, the faster proper diagnostic and treatment is established, the better the chances of survival are for the animal.

Reference:
Mace, S. Megaesophagus. Compendium on Continuing Education for the Practicing Veterinarian. Vol34, #2, février 2012.