Megaesophagus means enlarged esophagus. When the esophagus is partially obstructed over a period of time, it gradually enlarges like a balloon and becomes a storage organ. This process, called megaesophagus, is accompanied by regurgitation, loss of weight, and recurrent episodes of aspiration pneumonia.
There are two causes of megaesophagus. The first is a failure of the esophagus to contract and propel food into the stomach. This impaired motility occurs as a hereditary disorder in puppies and as an acquired disease in adults. The second cause of megaesophagus is a physical blockage, such as a foreign body or a developmental problem with abnormal blood vessels that encircle the esophagus.
Congenital megaesophagus is a hereditary form of the disease that occurs in puppies. It is caused by a developmental disorder involving the nerve plexus in the lower esophagus. Peristaltic activity stops at the level where the esophagus is paralyzed, and food can go no further. In time, the esophagus above the inert segment enlarges and balloons out. This can be seen by lifting the puppy by his back legs and looking for a bulging out of the esophagus at the side of the neck.
Congenital megaesophagus has been described in German Shepherd Dogs, Golden Retrievers, Great Danes, Irish Setters, Greyhounds, Labrador Retrievers, Newfoundlands, Miniature Schnauzers, Chinese Shar-Pei, and Wire Fox Terriers. Hereditary myopathies are other causes of congenital megaesophagus.
Puppies with congenital megaesophagus show signs at weaning, when they begin to eat solid foods. Characteristically, they approach the food dish with enthusiasm but back away after a few bites. They often regurgitate small amounts of food, which they eat again. After repeatedly eating the food, it becomes quite liquid and passes into the stomach. Repeated inhalation of food causes bouts of aspiration pneumonia.
Another type of congenital megaesophagus is caused by retained fetal arteries in the chest. The arteries produce a constriction around the esophagus (known as vascular ring anomaly) that prevents swallowing. The most common anomaly is a persistent right aortic arch. Regurgitation and difficulty swallowing appear at 4 to 10 months of age. These puppies are stunted and malnourished.
Adult-onset megaesophagus is an acquired condition that occurs with several rare neuromuscular diseases, including myasthenia gravis. Other known causes are hypothyroidism, hypoadrenocorticism, esophagitis, autoimmune diseases, and heavy metal poisoning. In most cases the cause is unknown.
A chest X-ray may show an enlarged esophagus, opaque material in the esophagus, or aspiration pneumonia. The diagnosis can be confirmed by administering a barium meal and then taking an X-ray of the chest. Ultrasound will also detect megaesophagus.
Treatment: The primary goals are maintaining nutrition and preventing complications. Divide a puppy's daily ration into four or more small meals. It is important to provide food and water from raised bowls to maximize the effects of gravity. A semiliquid or gruel mixture is easier for some dogs to swallow.
Others do better with solids. This should be determined by trial and error. If possible, the dog should remain standing up - that is, front feet on a stepstool or ladder - for 15 to 30 minutes after eating so gravity will help move the food into the stomach.
Even with dedicated care, many dogs with megaesophagus will remain somewhat stunted and have bouts of aspiration pneumonia. Episodes of aspiration pneumonia require antibiotics, selected after culture and sensitivity tests. Signs of pneumonia are coughing, fever, and rapid, labored breathing.
Puppies with congenital megaesophagus may eventually outgrow the condition. Surgical correction of some vascular ring anomalies is possible. Dogs with congenital megaesophagus should not be used for breeding. Adult-onset megaesophagus is irreversible, but some dogs do well for many years with careful attention to feeding and prompt treatment of respiratory infections.
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