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What is Megaesophagus?
The esophagus is the tube, which connects the mouth to the stomach.
When food is perceived in the esophagus, a neurological reflexes causing
muscle contraction and relaxation lead to rapid transport of the food
into the stomach, like an elevator going down. Other reflexes prevent
breathing during this swallowing process to protect the lungs from
aspiration.
When these reflexes are
interrupted such as by disease in the esophageal tissue or nerve
disease, the esophagus loses its ability to transport food. Instead the
esophagus loses all tone and dilates. The dilated, non-responsive
esophagus is called megaesophagus.
What are the symptoms of
megaesophagus?
The most common symptom of
megaesophagus is regurgitation. Regurgitation is a passive
return of food or liquids that have been ingested back to the mouth.
Regurgitated material is usually moist but not fully digested.
Vomiting, on the other hand, is a active process that involves the
muscles of the belly, diaphragm and ribs to actively expel stomach and
intestinal contents out of the mouth. As an owner, it is often
difficult to tell the difference between the two.
Because food moves randomly up
and down in a megaesophagus, it is not uncommon for some food to be
sucked into the lungs, which can lead to difficulty breathing from
pneumonia.
What Causes Megaesophagus?
Most cases are
young puppies (Great Danes, Irish setters, German Shepherds are
genetically predisposed). In these cases the condition is believed
congenital though it often does not show up until the pup begins to try
solid food. Congenital megaesophagus is believed to occur due to
incomplete nerve development in the esophagus. The good news is that
nerve development may improve as the pet matures. Prognosis is thus
better for congenital megaesophagus than it is for megaesophagus
acquired during adulthood.
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Another
congenital problem is the “Vascular Ring Anomaly.” This is a band of
tissue constricting the esophagus. Such tissue bands are remnants of
fetal blood vessels, which are supposed to disappear before birth. They
do not always do so. Improvement is obtained when the band is surgically
cut but in 60% of cases some residual regurgitation persists.
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In adult dogs,
diseases that cause nerve damage can lead to Megaesophagus. Myasthenia
gravis would be a common cause and very important to rule in or out.
Myasthenia gravis is a condition whereby the nerve/muscle junction is
destroyed. Signals from the nervous system sent to coordinate esophageal
muscle contractions simply cannot be received by the muscle.
Megaesophagus is one of its classical signs though general skeletal
muscle weakness is frequently associated. This condition is treatable
but special testing is needed to confirm it.
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Scarring in the
esophagus (as would occur after a foreign body episode or with damage to
the esophagus from protracted vomiting) may be sufficient to interrupt
neurological transmissions or even narrow the esophagus so that food
cannot pass through it. (Such a narrowing is called a “stricture.”)
Technically, this is not a true megaesophagus as the muscles are working
normally; there is simply an obstruction present. Special balloons can
be inserted in the esophagus to dilate the narrowed area but some
residual regurgitation is likely to persist. Tumors of the esophagus may
have similar effects in that they, too, can cause obstruction.
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Hypothyroidism
(reduced levels of thyroid hormones) may be associated with
megaesophagus. It is easy to rule thyroid disease in or out with blood
testing and it is important to treat a thyroid hormone deficiency;
however, megaesophagus usually does not correct with thyroid replacement
therapy. Whether or not hypothyroidism can truly cause megaesophagus is
still being debated.
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Addison's
disease (hypoadrenocorticism—an insufficient amount of adrenal steroid
hormones) has also been associated with megaesophagus.. This deficiency
alters the metabolism of esophageal muscle. Diagnosis and treatment are
not difficult.
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External
obstruction of the esophagus could cause a similar syndrome by creating
a blockage. A mass in the chest could pinch the esophagus closed.
Many of the above conditions are
treatable and it is important to find a cause for megaesophagus if it is
at all possible to do so. Unfortunately, most cases do not have a clear
cause and must be managed as they are. This can be hard work.
The Diagnostic Plan
Megaesphagus is diagnosed using
x-rays.. First, normal X-rays of the chest are taken. Sometimes the
enlarged esophagus is visible on these plain X-rays. More often,
contrast material (liquid barium) is given mixed with food and we take
X-rays while the dog is swallowing. The contrast will let us see the
outline of the esophagus. Sometimes, endoscopy is used to look down the
esophagus to find any lesions in the organ. Once the megaesohpagus is
verified, blood testing is used to rule in or out treatable causes of
megaesophagus such as hypothyroidism or hypoadrenocorticism.
Treatment
The first step is to determine
if the dog does better with a liquid or solid diet. Every individual is
different. One must train the dog to eat in an elevated position
(sitting up while eating). Ideally, the pet should be kept in this
position for 10-15 minutes after the meal.. Many pets do best eating
food shaped into a meatball and fed one at a time while sitting up.
Drugs to reduce stomach acidity
and to improve the tone of the lower esophageal sphincter may be
prescribed.
Some dogs may benefit from a
muscle motility modifier called cisapride.
If aspiration pneumonia is
present, it is treated with fluids and antibiotics as is any other
bacterial pneumonia, though these individuals may re-aspirate at any
time and require treatment all over again. Hospitalization may be
required.
Megaesophagus is a difficult
condition to manage. Treatment requires dedication and commitment and
still may produce variable results.
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