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== Introduction  ==

== Introduction  ==

Megaoesophagus describes a dilated, hypomotile oesophagus that is not able to effectively transport food from the the pharnyx to the stomach. The condition may be congenital or acquired and, although it occurs in most of the major domestic species, it is most common in dogs and cats. The following sections describe the causes of megaoesophagus.  

Megaoesophagus describes a dilated, hypomotile oesophagus that is not able to effectively transport food from the [[Pharynx - Anatomy & Physiology|pharnyx]] to the [[Monogastric Stomach - Anatomy & Physiology|stomach]]. The condition may be congenital or acquired and, although it occurs in most of the major domestic species, it is most common in dogs and cats. The following sections describe the causes of megaoesophagus.  

=== Congenital Megaoesophagus  ===

== Congenital Megaoesophagus  ==

==== Congenital Idiopathic Megaoesophagus  ====

=== Congenital Idiopathic Megaoesophagus  ===

[[Image:Megaoes.gif|thumb|left|125px|<small><center>Megaoesophagus (Copyright Alun Williams 2009 (RVC))</center></small>]] Congenital megaoesophagus is sometimes called 'congenital achalasia' but this term implies a defect of the cardiac sphincter of the stomach (as in man) whereas the canine condition affects the whole oesophagus. This disease is inherited in a number of breeds of dog, including the fox terrier (in an autosomal recessive manner), miniature Schnauzer (dominantly with 60% penetrance), great Dane, Irish setter, Chinese Shar-pei, Newfoundland and German shepherd. It is also an inherited disorder of the Siamese cat where it may occur with concurrent pyloric stenosis.  

[[Image:Megaoes.gif|thumb|left|125px|<small><center>Megaoesophagus (Alun Williams 2009 (RVC))</center></small>]] Congenital megaoesophagus is sometimes called '''congenital achalasia''' but this term implies a defect of the cardiac sphincter of the stomach (as in man) whereas the canine condition affects the whole oesophagus. This disease is inherited in a number of breeds of dog, including the Fox Terrier (in an autosomal recessive manner), Miniature Schnauzer (dominantly with 60% penetrance), Great Dane, Irish Setter, Chinese Shar-pei, Newfoundland and German Shepherd. It is also an inherited disorder of the Siamese cat where it may occur with concurrent pyloric stenosis.  

The disease is thought to result from a delay in the maturation of either upper motor neurones in the central swallowing centre in the brainstem or of the afferent sensory arm of the peristaltic reflex. The resultant hypomotility of the oesophagus leads to a functional obstruction and boluses of food do not reach the stomach and are eventually regurgitated. The condition is seen most commonly at 6-7 months during a period of rapid growth. Affected animals eat, regurgitate shortly afterwards and may then attempt to eat again. As with any disease that results in chronic regurgitation, affected animals lose weight due to '''malnutrition''' and may also develop '''aspiration pneumonia'''.  

The disease is thought to result from a delay in the maturation of either upper motor neurones in the central swallowing centre in the brainstem or of the afferent sensory arm of the peristaltic reflex. The resultant hypomotility of the oesophagus leads to a functional obstruction and boluses of food do not reach the stomach and are eventually regurgitated. The condition is seen most commonly at 6-7 months during a period of rapid growth. Affected animals eat, regurgitate shortly afterwards and may then attempt to eat again. As with any disease that results in chronic regurgitation, affected animals lose weight due to '''malnutrition''' and may also develop '''aspiration pneumonia'''.  

==== [[Myasthenia Gravis]]  ====

=== [[Myasthenia Gravis]]  ===

Myasthenia gravis is a disease of the neuromuscular junction that occurs due to a defect or absence of nicotinic acetylcholine receptors on the post-synaptic membrane (in the congenital form) or due to the presence of antibodies that bind to the receptors and prevent them from functioning normally (in the acquired form). The classical focal form of myasthenia gravis affects only the extraocular muscles, the cranial oesophagus and the muscles innervated by cranial nerves V, VII and IX. 80% of animals diagnosed with myasthenia gravis have megaoesophagus at presentation.  

Myasthenia gravis is a disease of the neuromuscular junction that occurs due to a defect or absence of nicotinic acetylcholine receptors on the post-synaptic membrane (in the congenital form) or due to the presence of antibodies that bind to the receptors and prevent them from functioning normally (in the acquired form). The congential form is primarily seen in breeds such as the Minitaure Daschund and Jack Russell Terrier and signs are usually seen from 6-8weeks of age. The acquired form occurs from 6+ months and is seen in breeds such as Labrador, Golden Retreiver and German Shepherd Dogs. The classical, focal form, of myasthenia gravis affects only the extraocular muscles, the cranial oesophagus and the muscles innervated by cranial nerves V, VII and IX and occurs in around 30% of cases. The generalised, exercise intolerance plus megaoesophagus form, is seen in 60% of cases. 80% of animals diagnosed with myasthenia gravis have megaoesophagus at presentation.

=== Acquired Megaoesophagus  ===

== Acquired Megaoesophagus  ==

Megaoesophagus may occur in any animal in which there is a disruption of the brain centres, reflex arcs or muscles responsible for normal peristalsis and tone along the oesophagus. Potential causes include:  

Megaoesophagus may occur in any animal in which there is a disruption of the brain centres, reflex arcs or muscles responsible for normal peristalsis and tone along the oesophagus. Potential causes include:  

*'''Brain Centres'''  

'''Brain Centres'''  

**'''Viral encephalitides''' including those syndromes caused by '''canine distemper virus'''.  

*'''Viral encephalitides''' including those syndromes caused by '''[[Canine Distemper Virus|canine distemper virus]]'''.  

**'''Presence of toxins''', including ingestion of '''lead''', '''mercury''', '''organophosphates''' and '''botulinum toxin''' and exposure to '''tetanus toxin'''

*'''Presence of toxins''', including ingestion of '''lead''', '''mercury''', '''organophosphates''' and '''botulinum toxin''' and exposure to '''tetanus toxin'''

*'''Reflex arcs'''  

 

**'''Peripheral neuropathies''', including labrador retriever myopathy and giant axonal neuropathy of German Shepherd dogs  

'''Reflex arcs'''  

**'''Feline dysautonomia''', also know as [[Oesophageal Dysautonomia|Key-Gaskell Syndrome]].

*'''Peripheral neuropathies''', including Labrador Retriever myopathy and giant axonal neuropathy of German Shepherd dogs  

*'''Muscle'''  

*'''Feline dysautonomia''', also know as [[Oesophageal Dysautonomia|Key-Gaskell Syndrome]].

**'''Myositis''' and '''polymyositis/polyneuritis'''  

 

**'''Glycogen storage disease''' type II.  

'''Muscle'''  

**'''Muscle weakness''' as occurs with severe '''hypokalaemia''' and '''[[Hypoadrenocorticism|hypoadrenocorticism]]''' (Addison's disease).

*'''Myositis''' and '''polymyositis/polyneuritis'''  

*Any cause of '''prolonged oesophageal obstruction''' may result in megaoesophagus which eventually becomes irreversible if the underlying cause is not removed. Examples include [[Oesophageal Foreign Body|foreign bodies]], [[Oesophageal Neoplasia|neoplasia]] and [[Oesophageal Stricture|strictures]].

*'''Glycogen storage disease''' type II.  

 

'''Muscle weakness''' as occurs with severe '''hypokalaemia''' and '''[[Hypoadrenocorticism|hypoadrenocorticism]]''' (Addison's disease).

 

Any cause of '''prolonged [[Impaction of the Oesophagus|oesophageal obstruction]]''' may result in megaoesophagus which eventually becomes irreversible if the underlying cause is not removed. Examples include [[Oesophageal Foreign Body|foreign bodies]], [[Oesophageal Neoplasia|neoplasia]] and [[Oesophageal Stricture|strictures]].

The result is the presence of a hypotonic [[Oesophagus - Anatomy & Physiology|oesophagus]] which is distended by accumulated food material. The thoracic oesophagus from the thoracic inlet to the diaphragm is usually dilated and affected animals regurgitate repeatedly, lose weight and may develop aspiration pneumonia.  

The result is the presence of a hypotonic [[Oesophagus - Anatomy & Physiology|oesophagus]] which is distended by accumulated food material. The thoracic oesophagus from the thoracic inlet to the diaphragm is usually dilated and affected animals regurgitate repeatedly, lose weight and may develop aspiration pneumonia.  

== Diagnosis  ==

== Diagnosis  ==

=== Diagnostic Imaging  ===

=== Diagnostic Imaging  ===

'''Endoscopy''' allows the operator to visualise the dilated oesophagus directly but this is rarely required to reach a diagnosis.  

'''Endoscopy''' allows the operator to visualise the dilated oesophagus directly but this is rarely required to reach a diagnosis.  

=== Diagnostic Tests  ===

=== Diagnostic Tests  ===

<br>Hematological and biochemical analysis of blood samples may be useful to diagnose several underlying causes of acquired megaoesophagus, such as myositis with an elevated creatine kinase (CK) concentration. Further tests, such as an ACTH stimulation test or T4/ TSH levels, may also be indicated if hypoadrenocortiscm is the suspected cause. Congenital idiopathic megaoesophagus is diagnosed in young animals (often of a predisposed breed) in which all other causes have been discounted.  

<br>Hematological and biochemical analysis of blood samples may be useful to diagnose several underlying causes of acquired megaoesophagus, such as myositis with an elevated creatine kinase (CK) concentration. Further tests, such as an ACTH stimulation test or T4/ TSH levels, may also be indicated if hypoadrenocortiscm is the suspected cause. Congenital idiopathic megaoesophagus is diagnosed in young animals (often of a predisposed breed) in which all other causes have been discounted.  

== Treatment  ==

== Treatment  ==

*Small boluses of food OR a liquid gruel should be fed to the animal little and often, depending on preference of the dog and owner, as this reduces the risk of aspiration.  

*Small boluses of food OR a liquid gruel should be fed to the animal little and often, depending on preference of the dog and owner, as this reduces the risk of aspiration.  

*The '''forelimbs of the animal should be raised''' for 10-15 minutes after each to meal to allow the food to reach the stomach.  

*The '''forelimbs of the animal should be raised''' for 10-15 minutes after each meal to allow the food to reach the stomach.  

*The animal should be monitored constantly by its owner for the development of signs of '''aspiration pneumonia''', a frequent recurrent problem in animals with congenital megaoesophagus. This condition should be treated aggressively with intra-venous bactericidal antibiotics (preferably selected on the basis of results from a culture of a broncho-alveolar lavage), coupage and nebulisation.<br>

*The animal should be monitored constantly by its owner for the development of signs of '''aspiration pneumonia''', a frequent recurrent problem in animals with congenital megaoesophagus. This condition should be treated aggressively with intra-venous bactericidal antibiotics (preferably selected on the basis of results from a culture of a broncho-alveolar lavage), coupage and nebulisation.

*Gastrostomy tubes have been shown to decreased the amount of regurgitation, however, some animals may still regurgitate saliva.<br>

== Prognosis  ==

== Prognosis  ==

Good to poor; depending on underlying cause.  

Good to poor; depending on underlying cause.  

Sudden death due to aspiration pneumonia is a risk that may occur at any time.  

Sudden death due to '''aspiration pneumonia''' is a risk that may occur at any time.  

== References  ==

== References  ==

Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company <br>[[Category:Oesophagus_-_Pathology]] [[Category:Oesophageal_Diseases_-_Cat]] [[Category:Oesophageal_Diseases_-_Dog]] [[Category:To_Do_-_Kate]] [[Category:Oesophageal_Diseases_-_Cattle]] [[Category:Oesophageal_Diseases_-_Horse]]

 

Ettinger, S.J. and Feldman, E. C. (2000) '''Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2''' (Fifth Edition) ''W.B. Saunders Company ''

 

 

 

 

 

 

 

[[Category:Oesophagus_-_Pathology]] [[Category:Oesophageal_Diseases_-_Cat]] [[Category:Oesophageal_Diseases_-_Dog]][[Category:Expert Review - Small Animal]][[Category:Expert Review - Farm Animal]][[Category:Expert Review - Horse]] [[Category:Oesophageal_Diseases_-_Cattle]] [[Category:Oesophageal_Diseases_-_Horse]]