| Megaesophagus | |
|---|---|
| Other names | Esophageal dilatation |
 | |
| Chagas megaseophagus | |
| Specialty | Gastroenterology |
Megaesophagus, also known asesophageal dilatation, is a disorder of theesophagus in humans and othermammals, whereby the esophagus becomes abnormally enlarged. Megaesophagus may be caused by any disease which causes the muscles of theesophagus to fail to properly propel food and liquid from the mouth into the stomach (that is, a failure ofperistalsis). Food can become lodged in the flaccid esophagus, where it may decay, beregurgitated, or be inhaled into the lungs (leading toaspiration pneumonia).[1]
Megaesophagus may occur secondary to diseases such asachalasia orChagas disease. Achalasia is caused by a loss ofganglion cells in themyenteric plexus. There is a marked lack of contraction within the muscles involved in peristalsis with a constant contraction of thelower esophageal sphincter. Dilation of the esophagus results in difficulty swallowing. Retention of foodbolus is also noted.[2]
Megaesophagus can also be a symptom of the diseasemyasthenia gravis. Myasthenia gravis is aneuromuscular disease where the primary symptom is weakness in various body parts of the dog. However, when myasthenia gravis occurs in older dogs it is thought of as animmune-mediated disease. Often when myasthenia gravis is diagnosed in older dogs the first symptom the dog may manifest is megaesophagus.[3]
Myasthenia gravis occurs whenacetylcholine receptors (nicotinic acetylcholine receptors) fail to function properly, so that the muscle is not stimulated to contract. There is an invention known as the "bailey chair" that uses the force of gravity to push down liquids and food into the dog's stomach. Usually dogs are known to understand when it is time to eat in their bailey chair, and this helps prevent issues. Bailey chairs can be made and are sold.[4] Also, a simple chair turned upside down can be successfully used for this purpose.
In two unrelated incidents inLatvia andAustralia megaesophagus developed in dogs that had eaten certain brands of dog food; however, no agent that could have caused the disorder has been found in lab tests of the food.[5][6][7]
An important distinction in recognizing megaesophagus is the difference between when a dog regurgitates or vomits. When a dog regurgitates there is usually not as much effort involved as when a dog vomits. Often when regurgitating, the dog will tip its head down and the liquid and/or food will almost appear to "spill out" of its throat.[citation needed]
One of the primary dangers to a dog with megaesophagus isaspiration pneumonia. Because the food stays lodged in the throat, it can often be inhaled into the lungs causing aspiration pneumonia. One way to avoid this is to make sure that every time the dog eats or drinks anything, that the dog sits for at least 10 minutes afterward or is held in a sitting up or begging position. This disorder has a guarded prognosis, however, a successful management technique is vertical feeding in a Bailey chair.[8]
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Affected breeds:
Megaesophagus is rare in horses.[9] It is more frequently reported inFriesian horses than in other breeds.[10]Congenital megaesophagus is usually identified when a foal begins to eat solid food from the ground; prior to this, as the foal nurses milk from its mother, the milk passes easily down into the stomach.[11] The most common signs are difficulty swallowing (dysphagia) and inhalational pneumonia.[11]