Megaesophagus

What it is

Megaesophagus is a diffuse dilation of the oesophagus with absent or ineffective peristalsis, so that swallowed food is not carried to the stomach. It is a syndrome rather than a single disease:

• Congenital idiopathic: appears at weaning, when puppies start eating solid food.
• Acquired secondary: caused by a neuromuscular or systemic disease, of which myasthenia gravis (focal or generalised) is the most important; others include hypoadrenocorticism, polymyopathies and polyneuropathies, and toxicoses.
• Acquired idiopathic: the most common form in adult dogs, with no cause found.

It must be distinguished from a segmental dilation cranial to an obstruction, such as a vascular ring anomaly (persistent right aortic arch) at the base of the heart, an oesophageal foreign body or a stricture.

Who it affects

Congenital forms are reported more often in the Irish setter, German shepherd, Great Dane, Labrador retriever, Newfoundland, miniature schnauzer and wire-haired fox terrier. Acquired forms affect adult dogs, mainly of large breeds.

Anatomy involved

• Oesophagus: the canine oesophagus is striated muscle along its whole length, so diseases of skeletal muscle and the neuromuscular junction (myasthenia gravis) affect it. The dilation involves the cervical and thoracic segments down to the cardia.
• Lungs: regurgitated material is aspirated, usually into the dependent lobes (right middle, right cranial and left cranial).

Clinical signs

Regurgitation — passive, effortless expulsion of undigested food or fluid, often tubular and covered in mucus, without the abdominal effort of vomiting — at variable times after eating. Weight loss or poor growth with a good appetite, and sometimes a visible bulge at the thoracic inlet. Cough, fever and dyspnoea point to aspiration pneumonia. Generalised myasthenia adds exercise-induced weakness.

Diagnosis

• Survey thoracic radiographs: a gas-, fluid- or food-filled oesophagus outlining the trachea dorsally ("tracheal stripe") and diverging the oesophageal walls toward the diaphragm; they also show aspiration pneumonia.
• Contrast studies or fluoroscopy: confirm the motility disorder and exclude segmental lesions; barium carries a risk of aspiration.
• Search for a cause: serum acetylcholine receptor antibodies (myasthenia gravis), baseline cortisol or ACTH stimulation test (hypoadrenocorticism), creatine kinase, thyroid tests and neurological examination.
• Endoscopy: for foreign bodies, strictures or oesophagitis.

Treatment

The underlying cause is treated when found (for example pyridostigmine for myasthenia gravis). Management is otherwise supportive and lifelong: feeding in an upright position (for example in a Bailey chair) and keeping the dog upright 10–20 minutes after meals, adjusting food consistency to what the dog tolerates best, and treating aspiration pneumonia early. A gastrostomy tube can be used when oral feeding fails. The prognosis depends on the cause and on the frequency of aspiration pneumonia; some puppies with the congenital form improve with age.