Megaesophagus in Mule

Background: Megaesophagus is a chronic dilation of the esophagus rarely found in horses. It’s a non-specific disease that is associated with several causes, and esophageal hypomotility is the dysfunction that most commonly results in organ dilation. In the literature, there are few reports of megaesophagus in horses and, to date, no cases in mule have been reported. The objective of this work is to describe a case of a donkey with thoracic megaesophagus.Case: A 16 year-old donkey, castrated male, mixed breed weighing 195 kg, was referred for clinical care with a history of 5 days of anorexia. On physical examination, apathy, cachexia, 8% dehydration, moderate enophthalmos, ptialism, bilateral nasal discharge, dry and bristling hair were observed. Due to the poor general condition, a nasogastric tube was chosen to perform enteral nutrition, however, it was not possible to progress the tube to the stomach. In order to confirm the suspicion of a possible esophageal obstruction, gastroscopy was performed, where it was possible to observe an esophageal dilation filled with bulky food located in the thoracic portion of the esophagus. In an attempt to stimulate esophageal motility, in order to promote the progression of the material present in the region of dilation, intramuscular metoclopramide was administered (two applications every 6 h), however the treatment had no effect. Due to the unfavorable prognosis and financial limitations of the owner, euthanasia was performed, which was followed by autopsy and histopathological examination. At necropsy, a marked dilation of the esophagus was observed in the thoracic portion, which was filled with approximately 500 grams of bulky food (grass). In the mucosa of this area, multiple ulcers were observed that occasionally coalesce, covered by a moderate amount of friable and yellowish-white material.Discussion: Megaesophagus is characterized by organ dilatation and enlargement, absence of peristalsis, presence of tertiary contractions and non-total or partial relaxation of the lower sphincter. Its origin can be congenital or secondary (acquired). In the congenital form, which corresponds to the hypomotility and generalized dilation of the esophagus, the main consequence is the underdevelopment of the foal after weaning. The acquired form occurs due to motor changes in the esophagus or gastroesophageal sphincter, causing passive dilation of the organ. Lupus erythematosus, polymyositis, polyneuritis, degenerative neuropathies, hypoadrenocorticism, hypothyroidism, thiamine deficiency, heavy metal poisoning (Lead and Thallium), tumors (mainly thymoma) and cervical injuries are among the main causes of secondary megaesophagus. Animals with esophageal paralysis or some type of esophageal obstruction, usually present nasal and oral reflux of saliva and may develop aspiration pneumonia, accompanied by nutritional deficiencies, weight loss, changes in normal development and the presence of esophageal ulcers. With the exception of pneumonia, the animal in the present report had all these signs. The prognosis of animals affected by megaesophagus is unfavorable. One of the ways to alleviate this disease is surgical treatment, however, complications such as dehiscence are common after esophageal surgery, mainly due to the fact that this organ does not have a serous layer, resulting in delayed healing. For this reason, euthanasia is considered in most cases. Megaesophagus is a non-specific and multifactorial disease that affects horses, and there are no reports in the literature in mules. In this case, endoscopy allowed the diagnosis to be made while still alive, however it was not possible to determine the primary cause of the disease.