The esophagus is the tube, which connects the mouth to the stomach. When food is perceived in the esophagus, a neurological reflexes causing muscle contraction and relaxation lead to rapid transport of the food into the stomach, like an elevator going down. Other reflexes prevent breathing during this swallowing process to protect the lungs from aspiration.
When these reflexes are interrupted such as by disease in the esophageal tissue or nerve disease, the esophagus loses its ability to transport food. Instead the esophagus loses all tone and dilates. The dilated, non-responsive esophagus is called megaesophagus.
What are the symptoms of megaesophagus?
The most common symptom of megaesophagus is regurgitation. Regurgitation is a passive return of food or liquids that have been ingested back to the mouth. Regurgitated material is usually moist but not fully digested. Vomiting, on the other hand, is a active process that involves the muscles of the belly, diaphragm and ribs to actively expel stomach and intestinal contents out of the mouth. As an owner, it is often difficult to tell the difference between the two.
Because food moves randomly up and down in a megaesophagus, it is not uncommon for some food to be sucked into the lungs, which can lead to difficulty breathing from pneumonia.
What Causes Megaesophagus?
Most cases are young puppies (Great Danes, Irish setters, German Shepherds are genetically predisposed). In these cases the condition is believed congenital though it often does not show up until the pup begins to try solid food. Congenital megaesophagus is believed to occur due to incomplete nerve development in the esophagus. The good news is that nerve development may improve as the pet matures. Prognosis is thus better for congenital megaesophagus than it is for megaesophagus acquired during adulthood.
- Another congenital problem is the “Vascular Ring Anomaly.” This is a band of tissue constricting the esophagus. Such tissue bands are remnants of fetal blood vessels, which are supposed to disappear before birth. They do not always do so. Improvement is obtained when the band is surgically cut but in 60% of cases some residual regurgitation persists.
- In adult dogs, diseases that cause nerve damage can lead to Megaesophagus. Myasthenia gravis would be a common cause and very important to rule in or out. Myasthenia gravis is a condition whereby the nerve/muscle junction is destroyed. Signals from the nervous system sent to coordinate esophageal muscle contractions simply cannot be received by the muscle. Megaesophagus is one of its classical signs though general skeletal muscle weakness is frequently associated. This condition is treatable but special testing is needed to confirm it.
- Scarring in the esophagus (as would occur after a foreign body episode or with damage to the esophagus from protracted vomiting) may be sufficient to interrupt neurological transmissions or even narrow the esophagus so that food cannot pass through it. (Such a narrowing is called a “stricture.”) Technically, this is not a true megaesophagus as the muscles are working normally; there is simply an obstruction present. Special balloons can be inserted in the esophagus to dilate the narrowed area but some residual regurgitation is likely to persist. Tumors of the esophagus may have similar effects in that they, too, can cause obstruction.
- Hypothyroidism (reduced levels of thyroid hormones) may be associated with megaesophagus. It is easy to rule thyroid disease in or out with blood testing and it is important to treat a thyroid hormone deficiency; however, megaesophagus usually does not correct with thyroid replacement therapy. Whether or not hypothyroidism can truly cause megaesophagus is still being debated.
- Addison’s disease (hypoadrenocorticism—an insufficient amount of adrenal steroid hormones) has also been associated with megaesophagus. This deficiency alters the metabolism of esophageal muscle. Diagnosis and treatment are not difficult.
- External obstruction of the esophagus could cause a similar syndrome by creating a blockage. A mass in the chest could pinch the esophagus closed.
Many of the above conditions are treatable and it is important to find a cause for megaesophagus if it is at all possible to do so. Unfortunately, most cases do not have a clear cause and must be managed as they are. This can be hard work.
The Diagnostic Plan of Our Veterinary Clinic:
Megaesophagus is diagnosed using x-rays. First, normal X-rays of the chest are taken. Sometimes the enlarged esophagus is visible on these plain X-rays. More often, contrast material (liquid barium as above) is given mixed with food and we take X-rays while the dog is swallowing. The contrast will let us see the outline of the esophagus. Sometimes, endoscopy is used to look down the esophagus to find any lesions in the organ. Once the megaesohpagus is verified, blood testing is used to rule in or out treatable causes of megaesophagus such as hypothyroidism or hypoadrenocorticism.
Treatment for Pets of Alta Loma, Rancho Cucamonga, Upland, Ontario, Claremont, Fontana and the Inland Empire:
The first step is to determine if the dog does better with a liquid or solid diet. Every individual is different. One must train the dog to eat in an elevated position (sitting up while eating). Ideally, the pet should be kept in this position for 10-15 minutes after the meal. Many pets do best eating food shaped into a meatball and fed one at a time while sitting up.
Drugs to reduce stomach acidity and to improve the tone of the lower esophageal sphincter may be prescribed. Some dogs may benefit from a muscle motility modifier called cisapride.
If aspiration pneumonia is present, it is treated with fluids and antibiotics as is any other bacterial pneumonia, though these individuals may re-aspirate at any time and require treatment all over again. Hospitalization may be required.
Megaesophagus is a difficult condition to manage. Treatment requires dedication and commitment and still may produce variable results.