Megaoesophagus in small animals

Please, DO NOT use the contents of this blog post as veterinary advice. The purpose of this blog is to help me revise for my exams. If your animal has any symptoms, consult with a registered veterinary surgeon as to what is the best course of treatment.

MEGAOESOPHAGUS IN SMALL ANIMALS

Contrast radiograph of dog with megaoesophagus (1)

Megaoesophagus, also known as dilatation of the oesophagus or oesophageal weakness, is exactly what it says on the tin! Due to several possible causes, the walls of the oesophagus become 'weak' and dilate, making it difficult for food to pass through to and stay in the stomach. 

This condition can be congenital or acquired. 

Congenital megaoesophagus can be caused by vascular ring anomalies, oesophageal diverticula, congenital myasthenia gravis or it can be idiopathic, in which case I believe the cause is still unknown, such as reported bu Nelson & Couto in 1998 - "no evidence of demyelination or neuronal degeneration and vagal efferent innervation appears to be normal".

Acquired (adult-onset) megaoesophagus can be primary (idiopathic) or secondary (due to systemic disease). The systemic diseases involved in the development of megaoesophagus in adult pets are myopathies/neuropathies, myasthenia gravis, systemic lupus erythematosus, hypoadrenocorticism, heavy metal toxicity (lead), dysautonomia (cats sometimes develop megaoesophagus due to this disorder), neoplasias, chronic oesophagitis (caused by gastrooesophageal reflux, persistent vomiting, hiatal hernia, caustic ingestion), Spirocera lupi,  dermatomyositis (usually occurs in collies), and possibly, hypothyroidism. In addition to these systemic diseases, oesophageal lesions such as oesophageal stricture, foreign body, neoplasias or extra-oesophageal compression can also lead to megaoesophagus.

Image showing oesophageal dilatation due to a vascular ring anomaly (2)

Clinical signs:

The main clinical sign of megaoesophagus is REGURGITATION (not vomiting)! This is a condition primarily found in dogs, although cats can occasionally be affected by it. Other clinical signs include painful swallowing and ptyalism, as well as coughing (because the regurgitated food can go down the trachea into the lungs). It is not uncommon that the only clinical sign visible, specially at the beginning of this condition, is the cough, due to the fact that some animals can re-swallow or re-eat the regurgitated material, making it impossible for people to know they present such clinical sign.

For puppies with congenital megaoesophagus, first signs of trouble usually appear while weaning when they are offered solid food. Such puppies are the smallest in their litter and generally look unwell, because they have very low nutrient intake due to the regurgitation. Sometimes, when pressure is applied to their abdomen this may cause ballooning of the oesophagus at the thoracic inlet.

A major complication of megaoesophagus is aspiration pneumonia and some of the clinical signs of this complicataion are cough, fever, nasal discharge (not always) and dyspnoea and/or orthopnoea. This is the main cause of death among animals with megaoesophagus, as it can happen even with the aspiration of saliva. 

Diagnosis:

Diagnosis of megaoesophagus is primarily done through radiographs with contrast. If the patient has acquired megaoesophagus, we have to perform diagnostic tests such as presence of antibodies to acetylcholine receptors (diagnostic for myasthenia gravis), ACTH-stimulation test (diagnostic for hypoadrenocorticism) and TSH-stimulation test (diagnostic for hypothyroidism) to determine the whether it is primary or secondary megaoesophagus because this will then dictate the treatment options and the prognosis for the patient.

Diverticula caused by oesophageal weakness occur occasionally and can be easy to mistake with oesophageal obstruction - BEWARE!

Treatment:

For secondary megaoesophagus, treat primary cause as fit for the specific cause. Congenital megaoesophagus sometimes resolves with age (around 6 months old). If it doesn't resolve with age or if it is an acquired primary megaoesophagus treatment consists in changing feeding habits. The patient must eat with their front limbs higher than their hind limbs and stay in this position 10-15 min after feeding, so that gravity helps food travel through the oesophagus and stay in the stomach. A Bailey chair is an invention that helps with this condition and patients seem to get used to them quite well (NatGeo video about Bailey chairs). It is preferable that food is offered in small and frequent portions. In case the patient is uncomfortable and has been regurgitating a lot, symptomatic treatment for oesophagitis can be administered for a few days alongside the change in feeding habits. There isn't an indication to use only dry food or only wet food - each animal reacts differently to different diets, so the best diet to a particular patient is always settled through trial and error.

Boxer in Bailey chair (3)

Prognosis:

If the underlying cause of secondary acquired megaoesophagus is found and treated successfully prognosis is good; prognosis is guarded if the patients respond well to dietary management (they still have the risk to develop aspiration pneumonia); and finally, prognosis is poor if the animal does not respond well to change in diet management as aspiration pneumonia is highly likely.

Sources: 

The Merk veterinary manual - 10th edition (2010)

Small animal internal medicine - Nelson & Couto (1998)

(1) https://www.vet.upenn.edu/about/press-room/publications/penn-vet-extra/penn-vet-extra-august-2015/the-stars-align-for-skye

(2) https://www.vettimes.co.uk/article/managing-vascular-ring-anomalies/

(3) https://www.pinterest.co.uk/pin/11470174030459364/