Introduction
Mega-esophagus and esophageal dysmotility are conditions caused by a number of neuromuscular, immune-mediated, infectious, neurological, rarely congenital, toxic, and possibly endocrine diseases, but many cases are idiopathic.
Mega-esophagus is segmental or global esophageal dilation due to loss of motor function with ineffective peristalsis, whereas esophageal dysmotility is poorly defined and can be clinical or subclinical and possibly a forerunner of mega-esophagus but certainly a complication of esophagitis (Bexfield, Watson, and Herrtage 2006). Clinical signs include regurgitation, dysphagia, and aspiration pneumonia. Breeds that are most commonly affected by mega-esophagus include the German Shepherd Dog (GSD) and the Great Dane, with the GSD, Golden Retriever and Irish Setter breeds having a higher risk factor for developing megaesophagus (Harvey et al. 1974; Gaynor, Shofer, and Washabau 1997; Strombeck 1978). Breeds affected by dysmotility include Bouvier des Flanders, Shar Pei and young terrier breeds (Peeters and Ubbink 1994; Stickle et al. 1992, and Bexfield et al. 2006). Earlier investigations report females being more commonly represented but later studies did not confirm sex or reproductive status as a risk factor. Supportive care is the mainstay of therapy in this syndrome as despite diagnosing the etiology of the mega-esophagus the clinical signs may be refractory to medical therapy, often requiring life-long treatment and management. Death is most commonly ascribable to complications including aspiration pneumonia or poor quality of life as assessed by the owner.Congenital diseases associated with megaesophagus, where clinical signs become apparent shortly after weaning, include idiopathic congenital mega-esophagus or secondary mega-esophagus due to congenital myasthenia gravis (MG), vascular ring anomalies (VRA), esophageal hiatal hernia and pituitary dwarfism. Other diseases that cause mega-esophagus, dysmotility, and regurgitation, include MG, esophagitis, inflammatory myopathies, infectious diseases, caudal esophageal neoplasia, degenerative peripheral neuropathies, endocrinopathies, hereditary myopathies, and toxicities.
When no underlying disease is detected the condition is considered idiopathic. Dogs are spontaneously afflicted between 5-12 years of age (Johnson, Denovo, and Mears 2008). Idiopathic mega-esophagus differs from achalasia in that the lower esophageal sphincter is normal in the former. Esophageal achalasia is the absence of esophageal peristalsis and inadequate lower esophageal relaxation due to functional loss of the myenteric plexus ganglion cells in the distal esophagus (Kempf. Beckmann, and Kook 2014). It has been described as a rare acquired syndrome in dogs (Boria, Webster, and Berg 2003). It can be accompanied by mega-esophagus (Boria et al. 2003).