Megaesophagus
Encyclopedia
Megaesophagus is a condition in humans, cats and dog
s where peristalsis
fails to occur properly and the esophagus
is enlarged. Normally, when the dog's esophagus is functioning properly, it acts as a muscle and pushes the food down the esophagus into the stomach
. However, when a dog has megaesophagus, the esophagus stays enlarged and does not push the food down to the stomach. Therefore, the food fails to enter the stomach and often stays in the esophagus, and is eventually regurgitated
, or enters the lungs through breathing, or decays in the esophagus.
In human pathology a condition known as achalasia
may predispose a person to slowly develop megaesophagus. Achalasia is due to the loss of ganglion cell
s of the myenteric plexus. It occurs mostly in middle aged adults. There is a marked lack of contraction in the muscle contractions involving peristalsis with a constant contraction of the lower esophageal sphincter
. Dilation of the esophagus results in difficulty swallowing. Retention of food bolus
is also noted. Chagas disease
is one cause of megaesophagus in humans. Achalasia also predisposes to esophageal carcinoma
.
Megaesophagus can also be a symptom of another disease in dogs called myasthenia gravis
. Myasthenia gravis is a neuromuscular disease
where the primary symptom is weakness in various body parts of the dog. However, when myasthenia gravis occurs in older dogs it is thought of as an immune-mediated disease
. Often when myasthenia gravis is diagnosed in older dogs the first symptom the dog may manifest is megaesophagus.
Myasthenia gravis occurs when acetylcholine receptor
s (nicotinic acetylcholine receptors or AChRs) fail to function properly. Due to the inability of the nerve receptors to function appropriately, the muscles fail to have a stimulus that causes them to contract.
An important distinction in recognizing megaesophagus is the difference between when a dog regurgitates or vomits. Regurgitating is a common symptom of megaesophagus while vomiting is not necessarily associated with megaesophagus. When a dog regurgitates there is usually not as much effort involved as when a dog vomits. Often when regurgitating, the dog will tip its head down and the liquid and/or food will almost appear to "spill out" of its throat.
One of the primary dangers to a dog with megaesophagus is aspiration pneumonia
. Because the food stays lodged in the throat, it can often be inhaled into the lungs causing aspiration pneumonia. One way to avoid this is to make sure that every time the dog eats or drinks anything, that the dog sits for at least 10 minutes afterwards or is held in a sitting up or begging position. This requires that all food and liquid intake be closely monitored and specifically administered to the dog in regular intervals (sometimes as often as 2-3 hours) in smaller quantities. Obviously, if smaller quantities of food and water are administered, one needs to take the necessary precaution to ensure the dog has a sufficient caloric and water intake. The prognosis for this condition is guarded.
An extensive list of breeds affected via known familial predisposition may be found at Genetic Predisposition
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
s where peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...
fails to occur properly and the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
is enlarged. Normally, when the dog's esophagus is functioning properly, it acts as a muscle and pushes the food down the esophagus into the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
. However, when a dog has megaesophagus, the esophagus stays enlarged and does not push the food down to the stomach. Therefore, the food fails to enter the stomach and often stays in the esophagus, and is eventually regurgitated
Regurgitation (digestion)
Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.Regurgitation is used by a number of species to feed their young...
, or enters the lungs through breathing, or decays in the esophagus.
In human pathology a condition known as achalasia
Achalasia
Achalasia , also known as esophageal achalasia, achalasia cardiae, cardiospasm, and esophageal aperistalsis, is an esophageal motility disorder involving the smooth muscle layer of the esophagus and the lower esophageal sphincter...
may predispose a person to slowly develop megaesophagus. Achalasia is due to the loss of ganglion cell
Ganglion cell
A retinal ganglion cell is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells...
s of the myenteric plexus. It occurs mostly in middle aged adults. There is a marked lack of contraction in the muscle contractions involving peristalsis with a constant contraction of the lower esophageal sphincter
Cardia
The cardia is the anatomical term for the part of the stomach attached to the esophagus. The cardia begins immediately distal to the z-line of the gastroesophageal junction, where the squamous epithelium of the esophagus gives way to the columnar epithelium of the gastrointestinal tract.Just...
. Dilation of the esophagus results in difficulty swallowing. Retention of food bolus
Bolus (digestion)
In digestion, a bolus is a mass of food that has been chewed at the point of swallowing. Once a bolus reaches the stomach, digestion begins....
is also noted. Chagas disease
Chagas disease
Chagas disease is a tropical parasitic disease caused by the flagellate protozoan Trypanosoma cruzi. T. cruzi is commonly transmitted to humans and other mammals by an insect vector, the blood-sucking insects of the subfamily Triatominae most commonly species belonging to the Triatoma, Rhodnius,...
is one cause of megaesophagus in humans. Achalasia also predisposes to esophageal carcinoma
Esophageal cancer
Esophageal cancer is malignancy of the esophagus. There are various subtypes, primarily squamous cell cancer and adenocarcinoma . Squamous cell cancer arises from the cells that line the upper part of the esophagus...
.
Megaesophagus can also be a symptom of another disease in dogs called myasthenia gravis
Myasthenia gravis
Myasthenia gravis is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatiguability...
. Myasthenia gravis is a neuromuscular disease
Neuromuscular disease
Neuromuscular disease is a very broad term that encompasses many diseases and ailments that either directly, via intrinsic muscle pathology, or indirectly, via nerve pathology, impair the functioning of the muscles....
where the primary symptom is weakness in various body parts of the dog. However, when myasthenia gravis occurs in older dogs it is thought of as an immune-mediated disease
Immune-mediated disease
Immune-mediated diseases are conditions which result from abnormal activity of the body's immune system. The immune system may over-react or start attacking the body . Autoimmune diseases are a subset of immune-mediated diseases....
. Often when myasthenia gravis is diagnosed in older dogs the first symptom the dog may manifest is megaesophagus.
Myasthenia gravis occurs when acetylcholine receptor
Acetylcholine receptor
An acetylcholine receptor is an integral membrane protein that responds to the binding of acetylcholine, a neurotransmitter.-Classification:...
s (nicotinic acetylcholine receptors or AChRs) fail to function properly. Due to the inability of the nerve receptors to function appropriately, the muscles fail to have a stimulus that causes them to contract.
An important distinction in recognizing megaesophagus is the difference between when a dog regurgitates or vomits. Regurgitating is a common symptom of megaesophagus while vomiting is not necessarily associated with megaesophagus. When a dog regurgitates there is usually not as much effort involved as when a dog vomits. Often when regurgitating, the dog will tip its head down and the liquid and/or food will almost appear to "spill out" of its throat.
One of the primary dangers to a dog with megaesophagus is aspiration pneumonia
Aspiration pneumonia
Aspiration pneumonia is bronchopneumonia that develops due to the entrance of foreign materials into the bronchial tree, usually oral or gastric contents...
. Because the food stays lodged in the throat, it can often be inhaled into the lungs causing aspiration pneumonia. One way to avoid this is to make sure that every time the dog eats or drinks anything, that the dog sits for at least 10 minutes afterwards or is held in a sitting up or begging position. This requires that all food and liquid intake be closely monitored and specifically administered to the dog in regular intervals (sometimes as often as 2-3 hours) in smaller quantities. Obviously, if smaller quantities of food and water are administered, one needs to take the necessary precaution to ensure the dog has a sufficient caloric and water intake. The prognosis for this condition is guarded.
Breeds Affected
- Shar PeiShar PeiThe Shar Pei, or Chinese Shar-Pei, is a breed of dog known for its distinctive features of deep wrinkles and a blue-black tongue. The breed comes from China. The name translates to "sand skin" and refers to the texture of its short, rough coat...
- French BulldogFrench BulldogThe French bulldog is a small breed of domestic dog, related to the English bulldog and American bulldog.-History:The origin of the modern French Bulldog breed descends directly from the dogs of the Molossians, an ancient Greek tribe. The dogs were spread throughout the ancient world by Phoenician...
- German Shepherd DogGerman Shepherd DogThe German Shepherd Dog , also known as an Alsatian or just the German Shepherd, is a breed of large-sized dog that originated in Germany. The German Shepherd is a relatively new breed of dog, with its origin dating to 1899. As part of the Herding Group, the German Shepherd is a working dog...
- Great DaneGreat DaneThe Great Dane , also known as German Mastiff or Danish Hound , is a breed of domestic dog known for its giant size...
- GreyhoundGreyhoundThe Greyhound is a breed of sighthound that has been primarily bred for coursing game and racing, and the breed has also recently seen a resurgence in its popularity as a pedigree show dog and family pet. It is a gentle and intelligent breed...
- Irish SetterIrish SetterThe Irish Setter , is a setter, a breed of gundog and family dog. The term Irish Setter is commonly used to encompass the show-bred dog recognized by the American Kennel Club as well as the field-bred Red Setter recognised by the Field Dog Stud Book....
- Miniature SchnauzerMiniature SchnauzerThe Miniature Schnauzer is a breed of small dog of the Schnauzer type that originated in Germany in the mid-to-late 19th century. Miniature Schnauzers developed from crosses between the Standard Schnauzer and one or more smaller breeds such as the Poodle and Affenpinscher.The breed remains one of...
- Wire-haired fox terrierFox Terrier (Wire)The Wire Fox Terrier is a breed of dog, one of many terrier breeds. It is an instantly recognizable fox terrier breed. Although it bears a resemblance to the Smooth Fox Terrier, they are believed to have been developed separately.-Appearance:...
- Golden RetrieverGolden RetrieverThe Golden Retriever is a medium-sized breed of dog. They were historically developed as gundogs to retrieve shot waterfowl such as ducks and upland game birds during hunting and shooting parties. As such, they were bred to have a soft mouth to retrieve game undamaged and have an instinctive love...
- Labrador RetrieverLabrador RetrieverThe Labrador Retriever is one of several kinds of retriever, a type of gun dog. A breed characteristic is webbed paws for swimming, useful for the breed's original purpose of retrieving fishing nets. The Labrador is the most popular breed of dog by registered ownership in Canada, the United...
- Siamese (cat) Siamese (cat)The Siamese is one of the first distinctly recognized breeds of Oriental cat. The origins of the breed are unknown, but it is believed to be from Thailand. In Thailand, where they are one of several native breeds, they are called Wichian Mat...
- Persian (cat)
- American ShorthairAmerican ShorthairThe American Shorthair is a breed of cat believed to be descended from European domestic cats brought to North America by early settlers to protect valuable cargo from mice and rats...
- Purebred Shih tzu
An extensive list of breeds affected via known familial predisposition may be found at Genetic Predisposition
External links
- http://www.caninemegaesophagus.org/
- http://www.marvistavet.com/html/megaesophagus.html
- http://www.upei.ca/~cidd/Diseases/GI%20disorders/megaesophagus.htm
- http://www.gcvs.com/internists/megaesophagus.htm