Megaesophagus can be defined as loss of tone and motility of the esophagus, often resulting in diffuse dilation and clinical signs of regurgitation. Megaesophagus can be congenital, acquired or idiopathic (of undetermined cause). Meaning that it may be a defect that is present from birth or it can come on later in life .. Acquired megaesophagus is typically seen in both male and female dogs between 5 and 7 years of age. Any breed can develop megaesophagus but certain underlying conditions can have breed disposition.
There are many causes of acquired megaesophagus in adult dogs. Myasthenia Gravis is caused by antibodies to certain neuromuscular junctions causing muscle weakness of the esophagus. This is the most common cause of megaesophagus and accounts for up to 30% of megaesophagus cases. Other causes are dysautonomia, other problems with nerve signal transmission, laryngeal paralysis, Addison’s disease, severe esophagitis, neoplasia or esophageal foreign body to name a few. Any breed can be affected by megaesophagus but certain underlying conditions do have breed predispositions. Myasthenia Gravis in particular is more common in German Shepherds, Golden Retrievers, Labrador Retrievers, Akitas, Newfoundlands and Great Danes. Idiopathic megaesophagus occurs more commonly in large breed dogs.
Pet owners most commonly notice that their dog is regurgitating liquid or food. Regurgitation can occur right after eating or up to several hours later. Regurgitation is a passive act, it does not have the abdominal heaving that occurs with vomiting. Bile should not be seen in regurgitated contents. Other signs may be bad breath, excessive drooling and vomiting. In cases where a dog has aspirated food particles or water and has developed aspiration pneumonia the dog may be lethargic, coughing, have difficulty breathing and have nasal discharge.
Diagnosis of megaesophagus may incorporate many different diagnostic tests. X-rays of the chest may be used to diagnose generalized megaesophagus. A liquid called barium may be used to highlight the esophagus on x-rays to make it easier to see. In animals with presumed acquired megaesophagus a complete blood count, comprehensive blood chemistry as well as a urinalysis should be performed. Based on the results of these tests more specific testing may be required.
Treatment is geared toward treating the underlying cause of the megaesophagus as well as limiting regurgitation, providing appropriate nutrition, and prevention of aspiration pneumonia. Megaesophagus is treated with a medication called pyridostigmine bromide that is given by mouth 2 – 3 times a day for life. Dogs with megaesophagus often require special feeding requirements. To minimize regurgitation, aspiration and ensure adequate nutrition is obtainable these dogs should be fed while sitting in an upright position and remain in that position for up to 20 minutes after eating. THis is to allow gravity to assist the movement of food and water out of the esophagus and into the stomach.
Prognosis for dogs with megaesophagus is dependent upon early diagnosis, appropriate feeding techniques, and recognition and treatment of aspiration pneumonia. For dogs with idiopathic megaesophagus prognosis is poor as no underlying cause can be identified and treated. In patients with diagnosed myasthenia gravis remission within a year is possible with treatment.