Abstract

Megaesophagus, also known as esophageal dilatation, is a disorder of the esophagus in humans and other mammals, whereby the esophagus becomes abnormally enlarged. Megaesophagus may be caused by any disease which causes the muscles of the esophagus to fail to properly propel food and liquid from the mouth into the stomach (that is, a failure of peristalsis). Food can become lodged in the flaccid esophagus, where it may decay, be regurgitated, or may be inhaled into the lungs (leading to aspiration pneumonia).

Humans

Megaesophagus may occur secondary to diseases such as achalasia or Chagas disease. Achalasia is caused by a loss of ganglion cells in the myenteric plexus. There is a marked lack of contraction within the muscles involved in peristalsis with a constant contraction of the lower esophageal sphincter. Dilation of the esophagus results in difficulty swallowing. Retention of food bolus is also noted.

Other animals | Dogs

Megaesophagus can also be a symptom of the disease myasthenia gravis. Myasthenia gravis is a neuromuscular 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 an immune-mediated disease. Often when myasthenia gravis is diagnosed in older dogs the first symptom the dog may manifest is megaesophagus.

Myasthenia gravis occurs when acetylcholine receptors (nicotinic acetylcholine receptors) fail to function properly, so that the muslce is not stimulated to contract.

Other animals | Dogs | Diagnosis

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.

One of the primary dangers to a dog with megaesophagus is aspiration 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 afterwards 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.

Other animals | Cats

Affected breeds:

- American Shorthair

- Persian (cat)

- Siamese (cat)

Other animals | Horses

Megaesophagus is rare in horses. It is more frequently reported in Friesian horses than in other breeds. 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. The most common signs are difficulty swallowing (dysphagia) and inhalational pneumonia.