When an animal vomits there is a neural reflex, coordinated via the brainstem, such that its airways are temporarily closed off and protected from inhalation of material whilst the vomitus is ejected. Regurgitation is a passive process whereby food is returned via the mouth with no protection of the airways and there is real risk of inhalation. Thus the management of regurgitating patients is aimed not just at any underlying cause, but also at trying to prevent and/or treat inhalation.
Regurgitation is a hallmark of oesophageal disease and is caused by one or a combination of three simple mechanisms:
Megaoesophagus, the failure of peristalsis
Oesophagitis, the inflammation of the oesophageal lining
Oesophageal obstruction by extraluminal, intramural or intraluminal lesions
Typically, all three cause passive regurgitation: one exception is the animal with severe oesophagitis and/or recent stricture, when swallowing may appear uncomfortable and the patient actively returns food boluses via the mouth.
Secondary respiratory signs of oesophageal disease (e.g., nasal discharge, cough, dyspnoea) occur because regurgitation is not a reflex and the airway is not protected during the process, with a significant risk of nasopharyngeal reflux and/or inhalation. These signs are important because death from oesophageal disease is most commonly associated with inhalation pneumonia.
Specific treatment of specific oesophageal diseases follows a diagnosis made by plain radiographs and/or barium swallow ± fluoroscopy and/or endoscopy. For example, foreign bodies can be removed endoscopically, under fluoroscopic guidance or surgically. Vascular ring anomalies and hiatal hernias can be treated surgically.
A number of conditions can cause oesophagitis, which can be managed by symptomatic treatment with sucralfate to coat any ulceration, acid blockers (H2 antagonists or proton pump inhibitors) to reduce the acidity of any reflux, and metoclopramide (or cisapride if available) to reduce gastrooesophageal reflux. Feeding of blenderised foods is recommended, and biscuits and bones should be avoided. Severe oesophagitis can lead to a stricture which must be treated by balloon dilatation under endoscopic guidance.
Megaoesophagus (MO) is defined as oesophageal dilatation and dysfunction/paralysis and is characterised by a failure of progressive peristaltic waves. It can be idiopathic or secondary. Secondary MO may be caused by or at least be associated with a variety of underlying conditions. There is an association with hypothyroidism reported in dogs, but the most important underlying cause is myasthenia gravis as the canine oesophagus is primarily striated muscle and can therefore be affected by this autoimmune condition: approximately 25–30% of all canine MO cases have anti-ACh receptor antibody. The MO may be part of generalised myasthenia with obvious skeletal muscle weakness, but more often it manifests as focal disease affecting just the oesophagus and/or pharynx. Myasthenia gravis can also be congenital and is seen occasionally in association with thymoma.
Generalised and focal myasthenia gravis can be treated initially with anticholinesterases (pyridostigmine), and ultimately immunosuppression with corticosteroids may be curative. However, balancing treatments is difficult: initially anticholinesterases cannot be swallowed effectively, and if injectable neostigmine is used it may be difficult to dose safely; then immunosuppression may worsen any inhalation pneumonia. Mycophenolate mofetil has been described as a successful alternative immunosuppressive treatment. However, spontaneous remission may occur without any treatment.
Oesophageal myasthenia is much rarer in cats, probably because of the greater proportion of smooth muscle along their oesophagus. Dysautonomia is a more common cause of MO, although following a feline epidemic in the UK in the 1980s, it is now uncommon and only seen sporadically in cats and rarely in dogs. Dysautonomia affecting the oesophagus may be managed by prokinetics.
Primary (idiopathic) MO is seen mostly in dogs, and can appear as a congenital or acquired problem. It is typically seen in large and giant breed dogs such as the Irish Setter, German shepherd, Newfoundland, Great Dane, and Irish Wolfhound. In some cases, the dog may outgrow the congenital condition, whilst the acquired idiopathic form seen in older dogs is not reversible. There is no specific treatment of idiopathic MO. In dogs, the majority of oesophageal muscle is striated and so prokinetic agents such as metoclopramide and cisapride are ineffective. Indeed by increasing the tone in the lower oesophageal sphincter, they may actually worsen the problem.
As there is no specific treatment for primary MO, the patient is managed with symptomatic care. Postural feeding, which allows gravity to deliver food to the stomach, is attempted. The principle requires the oropharynx to be higher than the stomach so that food falls to the stomach. The use of feeding bowls on small stands is inadequate, but holding cats and small dogs vertically is feasible. For large dogs, feeding on the stairs or from a kitchen work-surface achieves similar results. In recent years the "Bailey Chair" has been invented, in order to keep the patient in the correct position during feeding. Logic would suggest gravity would allow preferential delivery of liquidised food to the stomach. However, there is often a greater risk of inhalation, and some patients actually cope better with sticky 'meatballs' or textured food (e.g., kibble).
The prognosis in most cases of idiopathic MO is grave because of inhalation pneumonia, although a few patients manage. Inhalation pneumonia is usually devastating both because aspiration keeps recurring, and because orally administered antibiotics frequently never pass the oesophagus. Furthermore, malnourishment of the patient suppresses immune responses. Parenteral antibiotics and/or gastrostomy tubes may be used if aggressive treatment is opted for, but usually the patient does poorly long term because it continues to inhale saliva. The prognosis is so poor because of the danger of recurrent aspiration and subsequent pneumonia, but some young dogs with congenital MO may recover spontaneously.
References
1. Washabau RJ. Disorders of the pharynx and oesophagus. In: Hall EJ, Simpson JW, Williams DA, eds. BSAVA Manual of Canine & Feline Gastroenterology. 2nd ed. BSAVA; 2005.
2. www.ehow.com/how_4843356_build-bailey-chair-dogs.html
3. petprojectblog.com/archives/dogs/megaesophagus-and-the-bailey-chair/