The esophagus is a muscular, distensible organ that carries food from the mouth to the stomach. Megaesophagus is a common disorder in dogs that describes slow motility with resultant dilation of the esophagus. As a result of hypomotility, food will “pool” in the esophagus and stretch it. The stretching leads to damage to the nerves. This worsens hypomotility – a vicious cycle.
Megaesophagus can be either primary or secondary. In the primary case, an underlying cause is never discovered. It predominantly occurs in puppies, and rarely in an adult-onset form. Secondary occurs when some other predisposing condition such as myasthenia gravis, an autoimmune disease, develops, leading to the megaesophagus.
Primary Megaesophagus in Dogs
Unfortunately, some puppies are just born with a flaccid, slow-moving esophagus. Breeds that are genetically predisposed include the wire-haired fox terrier and miniature Schnauzer, but any breed can be affected. Initial symptoms may not be seen until a puppy is transitioned from maternal milk to dog food. Then symptoms of regurgitation and secondary pneumonia are noted. Regurgitation is different from vomiting. It occurs almost directly after a meal. Often the food comes back up with no effort, almost like a burp, and no digestion has occurred.
A frequent, secondary consequence of regurgitation is aspiration pneumonia. As a puppy regurgitates while inhaling, food and stomach acid can be pulled into the lungs. In these cases, puppies must be treated for aspiration. This can include oxygen therapy, nebulization and coupage, and sometimes antibiotics. Hospitalization may be needed if the pneumonia is severe.
There is no surgical treatment for this type of megaesophagus; it can be managed with a variety of life-style changes. These include feeding and watering in an upright position (using a Bailey chair) with small, frequent, calorically dense meals. Some dogs do better with gruel while others prefer meatballs. It will depend on each dog’s ability to swallow.
A recent study (2017) showed some improvement in dogs with idiopathic/congenital megaesophagus when treated with sildenafil (Viagra). More studies need to be conducted to determine if this is a viable treatment option.
Megaesophagus is a lifetime condition, and any dog born with it must be closely watched for signs of aspiration pneumonia through their life.
Vascular Ring Anomalies
An important type of megaesophagus to mention that is both congenital and secondary is due to a vascular ring anomaly. In some breeds of dogs, particularly German shepherds, an abnormal blood vessel can persist instead of regressing during development. The most common type is a persistent right aortic arch (PRAA). When a dog is born, that extra blood vessel causes constriction as the esophagus passes through the chest. In front of the vessel, the esophagus is dilated. As a puppy starts to eat dog food, it becomes trapped in the area, dilating the esophagus.
This IS a fixable condition with surgery. However, after surgical repair, hypomotility may persist due to esophageal damage. Rapid diagnosis and treatment are essential to a good outcome. Any puppy that develops regurgitation at weaning should be immediately evaluated. X-rays with and without contrast can be done to diagnose this condition. If a persistent vascular ring anomaly is diagnosed, surgery can be done to snip the extra vessel. This is generally conducted by a board-certified surgeon, but there are general practitioners who have performed this surgery as well.
The list of underlying causes for acquired megaesophagus is extremely long and includes muscle diseases like polymyositis, infectious disease such as tetanus, Addison’s disease, cancer, myasthenia gravis, toxins including lead and thallium, and trauma.
As with primary, there is no surgical correction for this. The underlying disease must be identified and treated. In some cases, this will significantly improve the megaesophagus, but due to the stretching, it does not always return to normal size and motility. As a result, megaesophagus may persist, leading to episodes of aspiration pneumonia.
One of the most common causes in older dogs is myasthenia gravis. This is a systemic, autoimmune illness in which the body’s immune system destroys important receptors in nerve endings. It results in generalized weakness, particularly worse after exercise. There is a medication to treat MG, and it can improve the motility of the esophagus.
Ruling out other causes can take an exhaustive list of diagnostics, so be patient while your veterinarian examines possible underlying causes. By keeping close tabs on your dog’s health and providing your veterinarian with a thorough history, the etiology of megaesophagus in dogs can often be discovered.