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 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 rolls 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. Further, 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. With regurgitation, food is swallowed from the mouth but never really goes very far beyond that point. Food sits in the esophagus until it simply falls back out the mouth. It comes on more like a burp or a cough with very little warning sensation. In the dog, megaesophagus is the most common cause of regurgitation.
WHAT KIND OF CONDITIONS CAUSE MEGAESOPHAGUS?
It depends on if we are talking about congenital megaesophagus (present at birth) or an acquired megaesophagus (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% 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% 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.
For more information about Myasthenia gravis Click here.
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.
HYPOADRENOCORTICISIM ("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.
For more information on Addison’s Disease Click here.
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.)
This condition involves a congenital blood vessel defect in the skin (usually of the face) and certain muscles. The abnormal blood vessels lead to poor oxygenation of affected tissues and inflammation results as tissue damage from lack of oxygen occurs. Scabs and ulcers of the muzzle 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 confirmed. Most pet owners believe their regurgitating pet is either coughing or vomiting and it is up to the veterinarian to determine if regurgitation is present. A radiograph of the chest is needed to confirm megaesophagus so the index of suspicion must be high despite the fact that the owner will most likely provide another description.
In most cases, the megaesophagus is fairly obvious on radiographs but this is not always the case. Because of the potential to aspirate the regurgitated material (i.e. inhale some of it into the lung), it is best to avoid the use of oral contrast material (Barium) if possible but some times that is simply not possible and the only way to see the esophagus is with contrast medium. If contrast material is used and a megaesophagus is confirmed, it is important to hold the patient vertical for 10-15 minutes to get all of the contrast into the stomach and minimize the chance of regurgitation. Barium is non-organic and cannot be removed from the lung if it is inhaled.
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 an aspiration pneumonia is present 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 megaesophagus is present.
Despite all the diagnostic tests, however, the majoritiy of megaesophagus cases are “idiopathic” which means that no underlying cause can be found. The typical patient is usually age 5-12 years in age and a large breed dog. If there is no defined underlying cause for a particular patient, 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. Experimentation with different food consistencies including water versus ice chips is necessary as there is no way to predict what works for an individual animal. 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 presented 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.
THE FEEDING TUBE
If elevated feeding is not providing adequate nutrition for the patient, there is an alternative: the gastric feeding tube. 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 that saliva, but the food regurgitation should be controlled with tube feeding.
The special feeding tubes can be placed in the stomach either surgically, endoscopically, or using special 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.
Food is administered 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 medications that might be helpful in the management of megaesophagus.
While this medication is most well 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. It turns out that 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.
Sildenofil opens the sphincter between the stomach and esophagus. This facilitates getting food out of the esophagus and into the stomach where it belongs.
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 esophageal muscle is not smooth muscle in the dog; 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 sildenofil rather than closing it with metoclopramide or cisapride.
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. Treatment requires dedication and commitment and still may produce poor results. Be sure your veterinarian has answered all your questions about this condition.
We highly encourage owners of megaesophagus dogs to join the Canine Megaesophagus (and Esophogeal Dysmotility Disorders) Newsgroup at:
Page last updated: 7/9/2020