What is Megaesophagus?
Normal canine chest radiograph (black “tube” on top left is the trachea, not the esophagus. The esophagus is much thinner and cannot be seen). Photo by MarVistaVet
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.
Yellow lines trace the outline of a megaesophagus in canine chest radiograph
Yellow lines trace the outline of a megaesophagus in this canine chest radiograph. Photo by MarVistaVet
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.
What kind of Conditions Cause Megaesophagus?
It depends on if we are talking about congenital megaesophagus (born with it) or an acquired megaesophagus that is usually developed during adulthood.
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 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 clearly 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.
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 megaesphagus so it is worth screening for the treatable ones.
Myasthenia gravis is considered the most common cause of canine megaesophagus and is the first condition to rule 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.
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.
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.
A condition once rare in the U.S. is also worth mentioning and that is dysautonomia. Dysautonomia patients have a 60% incidence of megaesphagus and 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.
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.
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.
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.
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 on-going problem and on-going 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.
After 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, the majority of megaesophagus cases are idiopathic, which means that no underlying cause can be found. The patient with idiopathic megaesophagus is usually age 5 to 12 years in age and a large breed dog. If there is no defined underlying cause, general management of the megaesophagus is implemented as described below.
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.
Regurgitation is not only messy, it leads to aspiration pneumonia, which is serious.
Graphic by MarVistaVet
To minimize the effect of gravity on the food (and thus minimize regurgitation) one must train the dog to eat in an elevated position. Elevated feeding can be accomplished in several ways and it is of such importance that we would like to review it further. For many dogs a stepladder with three or so steps works well. The food is placed on the top platform and the dog must eat with his forefeet on one of the upper steps and his rear feet on the lower steps. Ideally, the pet should be kept in this position for 10-15 minutes after the meal. Another simple option is to put the food on top of a cardboard box at neck level. These simple steps can substantially reduces the number of regurgitation episodes daily.
Isaac in Bailey Chair. Photo courtesy of the Yahoo! Megaesophagus Newsgroup
A more sophisticated, and probably more effective, option is the Bailey Chair, which allows not only for 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.
The Feeding Tube
If elevated feeding is not providing 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.
The feeding tubes can be placed in the stomach either surgically, endoscopically, or using stomach tube applicators. The tube exits the body from the side where it 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.
Casper in Bailey Chair. Photo courtesy of the Yahoo! Megaesophagus Newsgroup
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. With the tube, food is administered cleanly with no spillage. Some water in a syringe is used to clear the tube before and after feeding.
There are several that can be helpful.
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 in 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 esophagus. This facilitates getting food out of the esophagus and into the stomach where it belongs.
Metoclopramide and Cisapride
Both of these medications are motility modifiers, which means they stimulate the smooth muscles of the GI tract. This sounds like they might be helpful in generating some muscle tone in the flaccid megaesophagus, but they are not. The problem is that in dogs esophageal muscle is not smooth muscle; it is skeletal muscle. Neither medication improves motility in the esophagus but they do tighten the lower esophageal sphincter where the esophagus joins the stomach. In other words, these medications close the stomach, keeping food inside it from spilling out and being regurgitated. This sounds great and for some patients it is great, but for other patients the sphincter closes before food can get in, effectively locking food out, the opposite of what we are trying to accomplish. Most patients benefit from keeping the sphincter open with sildenafil rather than closing it with metoclopramide or cisapride..
Oz in Bailey Chair. Photo courtesy of the Yahoo! Megaesophagus Newsgroup
Gastroprotection / Antacids
Food that washes out of the stomach and into the esophagus carries stomach acid with it and this is very damaging to the esophagus. The acid causes pain, 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. In order to minimize this sort of esophageal damage, a medication called sucralfate is probably a good addition to the megaesophagus regimen. Sucralfate forms protective webbing 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 because the stomach acid is actually helpful if an aspiration pneumonia occurs. If there is acid in the aspirated material, it will be less encouraging to bacteria and provides 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.
Another medication geared at improving 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 on-going.
Megaesophagus can be a challenging condition to manage. It turns out that pneumonia management can be just as important as regurgitation management. Treatment requires dedication and commitment and still may produce poor results. Be sure your veterinarian has answered all your questions about this condition.
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