Esophageal diseases, including megaesophagus, can easily sneak up on the unsuspecting clinician if regurgitation, the cardinal
sign of esophageal disease, is not considered a differential diagnosis for an animal that presents for what the owner perceives
as vomiting. Failure to consider the possibility of regurgitation in the patient presented for vomiting could lead to delays
in diagnosis, treatment errors, and undesired consequences. Patients with megaesophagus are at risk of potentially life-threatening
complications such as aspiration pneumonitis, so early recognition of the problem of regurgitation is important to prompt
and appropriate diagnosis and treatment.
Megaesophagus overview
The cardinal clinical sign of megaesophagus is regurgitation, which must be distinguished from vomiting by careful historical
investigation. Compared to vomiting, regurgitation is a passive process that is not proceeded by prodromal signs such as lip-licking,
anxiousness, and repeated heaving/retching. Regurgitation can occur minutes to hours after ingestion of food or water. Distinction
between regurgitation and vomiting in some patients can be difficult, and if there is any doubt about whether a patient could
be regurgitating, it may be prudent to assess esophageal function before pursuing causes of vomiting.
Aspiration pneumonia is one of the most common complications of esophageal disease, including megaesophagus, in small animal
patients. In a recent study (Kogan et al) of canine aspiration pneumonia, esophageal dysfunction was one of the leading underlying
causes, noted in 35/88 dogs. In those 35 dogs, megaesophagus was the most common esophageal disorder, observed in 25. An important
set of observations that were noted in a companion article was that fewer than half of 88 dogs with aspiration pneumonia had
abnormalities of body temperature, heart or respiratory rates, and for 80 dogs in which lung sounds were described, abnormal
sounds were recorded in 55/80. Cough was described in only 57% of cases. Taken together, these reports show that aspiration
pneumonia is not readily excluded based on clinical signs and physical examination abnormalities; patients with risk factors
for aspiration pneumonia, such as megaesophagus, should have thoracic radiographs obtained as part of their routine evaluation.
Megaesophagus can be congenital or acquired, with acquired megaesophagus a much more common disease than congenital megaesophagus.
Although cats do develop megaesophagus, megaesophagus is seen more commonly in dogs.
Congenital megaesophagus
Congenital megaesophagus is seen in young to juvenile animals, and has a number of different causes. Idiopathic congenital
megaesophagus is believed to reflect afferent (sensory) dysfunction of the vagal nerve leading to poor esophageal contraction
in response to material in the esophageal lumen. Congenital myasthenia gravis can cause megaesophagus and reflects deficiencies
in the number of acetylcholine receptors at the neuromuscular junction (typically established by examination by examination
of external intercostal muscle biopsies). Congenital megaesophagus has been seen as part of a complex of other neurologic
abnormalities including laryngeal paralysis and peripheral weakness and has been termed laryngeal paralysis-polyneuropathy
complex; the complex has been described in related Dalmatians and Pyrenean mountain dogs. Megaesophagus can also be a consequence
of obstructive disease such as vascular ring anomalies.
Regurgitation of food or fluid is the most common clinical sign of congenital megaesophagus; poor weight gain in conjunction
with regurgitation is also common. Affected animals may have clinical signs of respiratory disease secondary to aspiration
events.
Diagnosis of congenital megaesophagus is typically established by demonstrating esophageal dilation either by plain thoracic
radiographs or contrast esophagrams. The underlying cause (e.g. vascular ring anomaly, acquired myasthenia gravis) defines
treatment and prognosis. Patients with some vascular ring anomalies are surgical candidates, and the prognosis is generally
considered better the sooner the surgical intervention occurs.
The prognosis for dogs with congenital idiopathic megaesophagus is fair. With time and proper supportive care, some dogs will
gain esophageal function as they grow older. The prognosis for other causes of congenital esophageal dysfunction is more guarded
as repeated aspiration events, and nutritional deficits, tend to characterize these animals.
