Megaesophagus

Megaesophagus
Chagas megaseophagus
Classification and external resources
ICD-9-CM	530.0
DiseasesDB	31519
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Megaesophagus, also known as ME, is a condition in humans, cats, dogs and horses where peristalsis fails to occur properly and the esophagus is enlarged. Normally, when the animal's esophagus is functioning properly, it acts as a muscle and pushes the food down the esophagus into the stomach. However, when an animal 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 cells of the myenteric plexus. It occurs mostly in middle aged adults. There is a marked lack of contraction within the muscles involved in 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 receptors (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.

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