For young puppies with megaesophagus, the condition is inherited. They will start to show signs by the time they start to eat solid foods. Miniature Schnauzers and Wire-Haired Fox Terriers are most likely to develop megaesophagus, and other breeds like German Shepherds, Labrador Retrievers, Great Danes, and Newfoundlands may be predisposed to it.
For young adults to middle-aged dogs, megaesophagus is acquired which means that there is some underlying cause besides genetics. Severe inflammation of the esophagus oresophagitis can also cause megaesophagus, and esophagitis itself can be caused by any number of diseases. Scarring or damage from a foreign body can cause a narrowing of the esophagus called a stricture which can obstruct it.
Any condition that causes nerve damage such as trauma, neurotoxin exposure, or myasthenia gravis can result in megaesophagus. Myasthenia gravis is thought to be the most common acquired cause of megaesophagus in dogs. It is an immune-mediated problem that attacks the junction between the nerves and muscles. Because of this, the swallow reflex signal is not conducted and megaesophagus results. Blood testing can help confirm a diagnosis, and dogs with myasthenia gravis are treated with a medication called pyridostigmine that is taken every day for the rest of their life.
Addison’s disease is a condition where the adrenal glands do not produce enough cortisol. Cortisol is necessary for many functions in the body, especially for the cellular metabolism of the esophageal muscles. When there isn’t enough cortisol, esophageal muscle function diminishes. Lifelong use of steroid injections and tablets are necessary for the treatment of Addison’s disease.
Structural defects and physical obstructions can also result in megaesophagus. Esophageal tumors can obstruct the esophagus so that food becomes stuck behind it and dilates the esophagus. Tumors can also invade the esophageal walls and muscles, resulting in problems with motility down to the stomach.
Certain parasites likeSpirocerca lupi can cause granulomas, which are raised areas that can develop inside of the esophagus. And in a condition known as persistent right aortic arch (PRAA), a small vessel that failed to disappear after a puppy’s birth traps the esophagus and becomes worse as the puppy grows. Surgery is necessary to ligate the vessel and free the esophagus.