What is Megaesophagus?
Megaesophaus refers to oesophageal dilation and reduced oesophageal motility. Such conditions can occur as a primary disorder, or secondary to oesophageal obstruction or a neuromuscular dysfunction.
Due to reduced or absent oesophageal motility, megaesophagus results in the accumulation and retention of food and fluid within the oesophagus. In normal unaffected dogs, reflex oesophageal motility occurs when food stimulates the sensory nerves in the oesophageal lining. Messages are sent back to the oesophagus which stimulate the oesophagus to contract. Any lesions along the pathway, including where the nerve joins the muscle tissue, may result in reduced motility and distention.
What are the Clinical Signs Showed by Dogs with Megaesophagus?
Standardly affected dogs have a history of regurgitating food and water, weight loss or poor growth, salivation and gurgling sounds. Where the megaesophagus is congenital and the dog is born with the condition (with signs first showing at weaning), the dog usually regurgitates fluid through the nostrils, and has a poor coat.
In some cases the regurgitation can lead to aspiration pneumonia, and where this occurs the dog may show signs of coughing, a pussy discharge from the nose and difficulty breathing.
Affected dogs regurgitate food during physical examination. They also are often poor performers with bad breath (caused by the food and fluid accumulating in the affected oesophagus), have increased salivation, and sometimes show a bulging of the oesophagus in the area where the oesophagus enters the thorax.
What are the Causes of Megaesophagus?
There are several causes of megaesophagus.
Congenital idiopathic megaesophagus - The cause is unknown and megaesophagus due to this condition is first seen at weaning. Such cause is more prevalent in fox terriers and minature schnauzers.
Oesophageal obstruction - It may due to the presence of an oesophageal foreign body, stricture, tumour, vascular ring anomaly (e.g. persistent right aortic arch), or a structure putting pressure on the outside of the oesophagus.
Neuromuscular diseases - These include myasthesia gravis, central nervous system lesion or secondary to tick paralysis.
Miscellaneous disorders - Such as infected oesopagus, Addisons disease and secondary to certain toxins.
How can Megaesophagus be Dignosed?
Most cases of megaesophagus are diagnosed using either radiology or endoscopy.
Affected oesophagus may be seen to be dilated with gas, fluid or ingested food on plain x-rays. Sometimes barium is required as a contrast agent to demonstrate the pooling and abnormal oesophageal motility.
In the case of endoscopy a scope is used to visualise the dilated oesophagus. It will also show the presence of any foreign bodies, tumours or oesophageal infection that may be the cause of megaesophagus.
How can Megaesophagus be Treated?
There is no surgical procedure that improve oesophageal motility, and generally surgery is not recommended (unless used to remove oesophageal foreign bodies, tumours or vascular ring anomalies. The treatment is a management procedure involving feeding in an upright position and feeding a gruel to reduce regurgitation.