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Normal swallowing: Coordinated muscle movements in the esophagus drive the food into the stomach. Photo by MarVistaVet

What is Megaesophagus?

Have you ever thought about how chewed-up food makes it from the throat to the stomach? The esophagus is the tube that connects the throat to the stomach, but the transport of food is far from passive. When food is perceived in the esophagus, a neurologic reflex causing sequential muscle contraction and relaxation leads to rapid transport of the food into the stomach, like an elevator going down. The process is active, highly coordinated, and includes other reflexes that close off the airways so that food material is not accidentally inhaled into the lungs.

When these reflexes are interrupted, such as by disease in the esophageal tissue or by nerve disease, the esophagus loses its ability to actively transport food. Instead, the esophagus loses all tone and enlarges (dilates). Reflexes protecting the lung are disrupted and aspiration pneumonia commonly follows. The flaccid air-filled esophagus that results is called a megaesophagus.

Vomiting Versus Regurgitation

When the esophagus loses all tone and dilates, it cannot coordinate the movement of food into the stomach properly. As a result, food tends to simply roll around in the esophagus according to gravity and ultimately tends to be regurgitated back onto the floor. This is not the same as vomiting; in fact, it is completely different.

Most people do not realize that there is a difference between vomiting and regurgitation. Vomiting is an active process. There is gagging, heaving, and retching as the body actively expels its stomach contents. Furthermore, there is an associated sensation of nausea allowing for some warning of what is about to occur. A nauseated patient looks uncomfortable and may drool or lick his lips prior to the vomiting motions. Regurgitation, on the other hand, is passive. Regurgitation is the hallmark sign of megaesophagus.

Yellow lines trace the outline of a megaesophagus in canine chest radiograph

Yellow lines trace the outline of a megaesophagus in canine chest X-ray.

What Causes Megaesophagus?

There are two types of megaesophagus: congenital megaesophagus (born with it) and acquired megaesophagus, which usually develops during adulthood.

Congenital Megaesophagus
Most cases involve young puppies; Great Danes, Irish setters, Newfoundlands, German Shepherds, Shar Pei, and Labrador retrievers are genetically predisposed. In these cases, the condition is believed to be 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, with recovery rates of 20-46 percent reported in different studies. Most puppies are diagnosed by age 12 weeks, though mild cases may not be abnormal until closer to age one year.

A similar congenital problem is the vascular ring anomaly. This is a band of tissue encircling and 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 percent of cases, some residual regurgitation persists.

Acquired Megaesophagus
Since the regurgitation involved in megaesophagus is challenging to manage, every effort should be made to minimize it. If the megaesophagus is secondary to another disease, then there is potential to treat that other disease and greatly improve or even resolve the megaesophagus. Many conditions have been associated with the development of megaesophagus, so it is worth screening for the treatable ones.

Myasthenia Gravis
Myasthenia gravis is considered the most common cause of canine megaesophagus and is the first condition to be ruled out. Myasthenia gravis is a condition whereby the nerve/muscle junction is destroyed immunologically. 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 and often resolvable, but special testing is needed to confirm it. Approximately 25% of dogs with acquired megaesophagus have myasthenia gravis.

Stricture
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 neurologic 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.

Hypoadrenocorticism (Addison's disease)
Addison's disease (hypoadrenocorticism) has also been associated with megaesophagus. This condition represents a deficiency of cortisone production by the adrenal gland. This deficiency alters the metabolism of esophageal muscle. Diagnosis and treatment are not difficult and, in this situation, the megaesophagus can frequently be resolved if not greatly improved with treatment.

Esophageal Obstruction
External obstruction of the esophagus could cause a similar syndrome by creating a blockage. A mass in the chest could pinch the esophagus closed. Depending on the situation, the obstruction could be relieved greatly, improving the regurgitation potential.

Dysautonomia
A condition once rare in the U.S. is also worth mentioning, and that is dysautonomia. Dysautonomia patients have a 60% incidence of megaesophagus, and it usually affects dogs living in rural areas. The syndrome involves a total disruption of the entire autonomic nervous system leading to difficulty urinating, dilated pupils, flaccid colon (megacolon), flaccid anal tone, poor tear production, and of course, megaesophagus. Successful treatment is unlikely, so it is helpful to recognize this constellation of signs from the beginning so that euthanasia can be considered. Testing for dysautonomia involves stimulating the autonomic nervous system with drugs and checking for response (increased heart rate in response to atropine injection, pupil constriction in response to pilocarpine eye drops, etc.) or lack thereof.

Dermatomyositis
This condition involves a congenital blood vessel defect in the skin, usually in the face and certain muscles. The abnormal blood vessels lead to poor oxygenation of affected tissues, and inflammation results as tissue damage occurs from lack of oxygen. The muzzle gets scabs, and ulcers result, but moderately affected dogs have muscle damage affecting facial muscles, and megaesophagus can result. Collies and Shetland sheepdogs are predisposed.

All these conditions must be sorted out in the megaesophagus patient, so let's review what happens in a typical evaluation of a regurgitating patient.

The Diagnostic Plan

First, the megaesophagus must be diagnosed. This is done with radiographs (x-rays). If megaesophagus is not obvious on plain films, it is better not to use contrast studies with barium if possible. This is because megaesophagus patients tend to inhale or aspirate food contents that back up in their throats. This is dangerous enough when the material is simply food, but if barium becomes inhaled, the body has great difficulty removing it from the lungs. Still, sometimes, this is the only way to see the megaesophagus.

Aspiration Pneumonia: A Potentially Life-Threatening Condition
The next step is to determine whether or not the animal has aspiration pneumonia from inhaling regurgitated food material. The same radiographs used to diagnose the megaesophagus can be used to determine if the pet has aspiration pneumonia, though just because the chest is clean at one point does not mean aspiration will not occur in the future. The owner of the megaesophagus dog must be vigilant for cough, listlessness, appetite loss, and/or nasal discharge. It is common for the megaesophagus patient to experience multiple episodes of aspiration pneumonia; it is an ongoing problem and ongoing concern as long as the pet has megaesophagus.

Chest radiographs in combination with a history of cough, nasal discharge, and the presence of fever, usually indicate pneumonia. Usually, the chest radiographs will show disease in the areas of the chest that are lowest in the standing animal, as this is where gravity draws inhaled material. Aspiration pneumonia makes the case much more serious as pneumonia can be a life-threatening condition.

Next Steps
After the megaesophagus has been confirmed and the patient has been assessed for aspiration, diagnostics continue as a search for a treatable underlying cause begins, and a search for the medical problems listed above begins. Despite all the diagnostic tests, however, the majority of megaesophagus cases are “idiopathic,” which means that no underlying cause can be found. If there is no defined underlying cause for a particular patient, general management of the megaesophagus is implemented as described below.

Treatment

Food Consistency
The first step is to determine if the dog does better with a liquid or solid diet. Experimenting with different food consistencies, including water versus ice chips, is necessary. Some animals do better with solid foods, and some do better with liquefied diets. If liquids are a problem, water can be provided in gelatin, mixed with a thickener, or given as ice cubes. Because so much nutrient material is lost in regurgitation, megaesophagus patients tend to be underweight. Adding a protein supplement such as whey protein powder can assist in maintaining a normal weight.

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Isaac in Bailey Chair. Photo courtesy of the Yahoo! Megaesophagus Newsgroup

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Casper in Bailey Chair. Photo courtesy of the Yahoo! Megaesophagus Newsgroup

Vertical Feeding
Vertical feeding can be accomplished in several ways, and there are different approaches to consider when discussing with your veterinarian so that you can find what works best for your dog.  If you have a small dog, you may use a front-pack baby or similar pet carrier or even a clean utility bucket (used only for feeding, not for cleaning) and gently stuff towels around your dog to be supported and comfortable while remaining upright to eat. 

Medium to large dogs often benefit from a Bailey Chair, which not only allows vertical feeding but also confines the patient for the post-feeding waiting period. The Bailey Chair was invented by the owners of a megaesophagus dog named Bailey. The more vertical the feeding, the less regurgitation is likely to result, and in some patients, regurgitation stops completely. The chair is relatively easy to construct, and the family who invented the chair is happy to send an instructional video.

They can be reached through the Megaesophagus Newsgroup (formerly through Yahoo).  Not feeling handy with constructing your own chair? Measure your dog and buy one.

Feeding Tubes
If vertical feeding does not provide adequate nutrition for the patient, the gastric feeding tube is an alternative. The tube allows food to be delivered directly into the stomach, skipping the diseased esophagus. This does not end regurgitation, as the animal will still be swallowing saliva throughout the day and periodically regurgitating it, but the food regurgitation should be controlled with tube feeding.

A feeding tube is placed by your veterinarian in the stomach either surgically, endoscopically, or using stomach tube applicators. The tube exits the body from the side which is comfortable for the pet. A protective bandage is used for daily wear and a clamp prevents leakage of stomach contents from the tube. The pet owner must be comfortable changing the dressings around the tube.

Food is given as a blended slurry through the tube. A liquid diet can be purchased, but usually, a thicker food is made with a blender. The tube administers food cleanly with no spillage. Some water in a syringe is used to clear the tube before and after feeding.

Medications
There are several that can be helpful, targeting different aspects of managing your dog's condition and keeping them as comfortable as possible.

Sildenafil
While this medication is best known for its human uses (its brand name is Viagra®), it is important to remember this medication has numerous effects on the autonomic nervous system. A common problem with megaesophagus is that the sphincter separating the esophagus and stomach is tightly closed. This keeps food from getting into the stomach, where it can be digested and moved forward, and leaves food pooling in the esophagus, where it can be regurgitated.

Sildenafil opens the sphincter between the stomach and the esophagus. This facilitates getting food out of the esophagus and into the stomach, where it belongs.

Metoclopramide and Cisapride
These medications are motility modifiers, which means they stimulate the smooth muscles of the GI tract. They also tighten the lower esophageal sphincter, which is a valve-like part at the end of the esophagus where it meets the stomach. In other words, these medications close the stomach, keeping food inside it from spilling out and being regurgitated. Some patients benefit from these medications, and others do better on sildenafil, which opens that valve instead. Your veterinarian can discuss with you what may work best for your dog.

Another medication that can help improve the muscle coordination and contraction strength of the esophagus is bethanechol. This medication helps strengthen the muscarinic nerve receptors in the esophagus, ultimately improving muscle tone there. Studies using this medication are ongoing.

Gastroprotection / Antacids
Food that washes out of the stomach and into the esophagus carries stomach acid with it, which is very damaging to the esophagus (the tube that connects the throat to the stomach). The acid causes pain and reluctance to swallow (possibly increasing the potential for aspiration) and can even yield scarring in the esophagus, further reducing any muscle activity the diseased esophagus still has.

To minimize this sort of esophageal damage, a medication called sucralfate is probably a good addition to the megaesophagus regimen. Sucralfate forms a protective coating over any inflamed areas in the esophagus, allowing for healing.

Antacids sound tempting to further mitigate the acid damage from regurgitated stomach contents, but it is best to avoid these if possible. The reason for this is that stomach acid is actually helpful if aspiration pneumonia occurs. If there is acid in the aspirated material, it will be less encouraging to bacteria and provide some protection to the patient. Since aspiration pneumonia is both serious and common, it may be best to preserve the natural protection the body offers for this situation.

Anti-nausea Medications
Esophagitis, an inflammation of the esophagus, can cause nausea, which can be treated with anti-emetic medications. These include Cerenia® (maropitant) or ondansetron.

Nebulizer Treatments
If your dog gets aspiration pneumonia, your veterinarian may recommend nebulizer treatments, which deliver lung medications in the form of a mist through a muzzle mask system. These treatments can help to open the lung’s air sacs and help your dog's congestion by loosening up mucous and debris there, allowing those things to come up and clear them with coughing. Your veterinarian will recommend a setup that is right for your dog if they need this treatment.

Prognosis and Summary

This is a life-long disease requiring owner dedication and commitment, and in some cases, can be challenging to manage. Some dogs may have continued issues throughout their lives. However, many dogs can have a high quality of life when the right balance of treatments and at-home management strategies are implemented.

• Prevention of aspiration pneumonia and regurgitation are key parts of managing megaesophagus to help your dog eat and swallow food safely and prevent complications.
• Medical treatments combined with various feeding and at-home care strategies can help your dog be as healthy and happy as possible.
• Be sure your veterinarian has answered all your questions about this condition, and always follow recheck recommendations.
• Many different megaesophagus communities may also be of help and encouragement.

Further resources:

https://www.k9megaesophagus.com 

http://caninemegaesophagusinfo.com