Page 590 - Clinical Small Animal Internal Medicine

558 Section 6 Gastrointestinal Disease

One of the most frequent complications of esopha- Specific Esophageal Disorders
VetBooks.ir geal disorders is aspiration pneumonia; this is the most Megaesophagus
common cause of death in animals with esophageal
motility disorders. Dogs with aspiration pneumonia
secondary to esophageal disease can present with fever, Congenital Megaesophagus
inappetence, coughing, mucopurulent nasal discharge, Megaesophagus is a condition characterized by diffuse
and pulmonary crackles. Dogs with chronic and severe esophageal dilation and decreased or absent esophageal
esophageal dysfunction may present with weight loss motility. Megaesophagus may be a congenital or acquired
and poor body condition scores secondary to (adult‐onset) disease. A familial predisposition has been
inadequate food intake. Dogs with foreign bodies or identified in several breeds including the Great Dane,
esophagitis are usually painful during swallowing. German shepherd, Irish setter, Chinese shar‐pei,
Foreign bodies are often associated with an acute onset Newfoundland, miniature Schnauzer, Labrador retriever
of regurgitation. The presence of esophageal disease at and fox terrier breeds, as well as Siamese cats. In the
the time of weaning is more commonly seen with con- wirehaired fox terrier, congenital megaesophagus is
genital idiopathic megaesophagus, vascular ring anom- inherited as a simple autosomal‐recessive trait, while in
alies or congenital stenosis. The history may indicate a miniature Schnauzers it is transmitted as either a simple
recent anesthetic procedure that could cause reflux autosomal‐recessive or dominant trait. Affected dogs
esophagitis and potential stricture, exposure to caustic usually start having clinical signs of regurgitation at or
medications (e.g., doxycycline) or foreign bodies. Signs shortly after weaning.
of concurrent neuromuscular disease can be seen in The main differential diagnosis that should be consid-
dogs with megaesophagus secondary to myasthenia ered in young dogs with regurgitation at the time of
gravis. weaning is a congenital vascular ring anomaly. Plain
radiographs are usually sufficient to differentiate between
these disorders, although contrast studies are necessary
Diagnostic Approach to Esophageal in some cases.
Disease The etiopathogenesis of congenital megaesophagus is
unclear. Esophageal motility and nerve stimulation stud-
Plain thoracic and cervical radiographs are the initial ies in dogs with megaesophagus indicate a defect in the
step in all animals with clinical signs and histories con- afferent neural pathway, while the efferent neural path-
sistent with esophageal disease. Radiographs are useful way appears to be intact.
in the identification of megaesophagus, radiopaque for- The prognosis for congenital megaesophagus is
eign bodies, and hiatal defects. In addition, the lungs and guarded to poor. Some dogs can be managed for months
mediastinum can be evaluated for any evidence of aspi- to years while others rapidly succumb due to uncon-
ration pneumonia or pneumomediastinum associated trolled regurgitation and aspiration pneumonia.
with esophageal perforation. Breeding of affected patients is not recommended.
A contrast esophagram should be considered when Treatment details for megaesophagus are discussed
plain radiographs do not identify a lesion. The contrast below.
study can be performed under fluoroscopy or using
plain radiography (see Chapter 53). The use of fluoros- Acquired Megaesophagus
copy helps in the evaluation of esophageal motility. Acquired megaesophagus can occur in any breed or age.
Contrast studies can be useful in the identification of Acquired megaesophagus may be primary (idiopathic)
radiolucent foreign material, strictures or neoplasia. or secondary to multiple disorders, particularly diseases
Contrast esophagram studies are usually contraindi- causing neuromuscular dysfunction.
cated in animals with megaesophagus because of the The most common cause of secondary acquired meg-
high risk of aspiration pneumonia. A water‐soluble iodi- aesophagus in dogs is myasthenia gravis(MG). MG may
nated contrast agent is preferred if esophageal perfora- be congenital (rare) or acquired. Acquired MG is an
tion is suspected. autoimmune disorder characterized by autoantibodies
Esophagoscopy can be useful for the diagnosis of directed against the acetylcholine (Ach) receptors of
esophageal neoplasia, esophagitis, strictures, and perfo- skeletal neuromuscular junctions. These antibodies bind
ration. This minimally invasive procedure allows the to the Ach receptors, reducing the number of receptors
direct visualization of the esophageal mucosa and lumen available for normal neuromuscular transmission. When
and can be used to obtain biopsies, retrieve foreign bod- acetylcholine is released from presynaptic vesicles at the
ies, balloon esophageal strictures or deploy esophageal nerve terminal, it is unable to bind to the receptors on
stents. the postsynaptic muscle fiber membrane. Depending on