Melena usually indicates the presence of significant upper gastrointestinal disease, although occasionally other diseases (such as clotting disorders, ingestion of blood, etc.) unrelated to the gastrointestinal tract may present with melena. The classic appearance of melena is black, shiny, sticky, foul-smelling feces with a tarry consistency. Melena may be seen as the only clinical sign, although other systemic signs often accompany it.
Ingestion of blood must be ruled out, including swallowing blood from the oral cavity or respiratory tract, and licking blood from a wound. A careful history and thorough physical examination of these patients is essential. The presence of melena generally warrants hospitalization, extensive diagnostic testing, and supportive care. It is best to determine the underlying cause and treat the specific problem.
There are many potential causes for melena. The most common causes are usually diseases of the gastrointestinal tract that create ulcerations or cause bleeding into the tract. Ingestion of blood or bleeding from clotting abnormalities can also cause melena. It is important to determine a cause, as specific treatment is necessary to successfully treat patients with melena. Infectious disorders such as intestinal parasites, viral, bacterial, and/or fungal infections should be ruled out.
Intestinal irritation and ulceration may occur with the administration of certain drugs, particularly corticosteroids and nonsteroidal anti-inflammatory agents (NSAIDs).
Gastrointestinal ulcerations or erosions commonly produce melena. Such ulcers may occur following acute gastric dilatation and volvulus (twisting of the stomach), heat stroke, overwhelming body infections, the overproduction of stomach acid, shock, anaphylaxis, and as a side effect of some cancers.
Gastrointestinal tumors or foreign bodies can cause bleeding and melena.
Certain metabolic diseases, such as kidney and liver failure, pancreatitis and hypoadrenocorticism (Addison's disease) can cause bleeding into the intestinal tract.
Inflammation of the walls of the intestines (inflammatory bowel disease) can be associated with melena.
Ingested blood should be considered as a cause when bleeding is present in the oral cavity or respiratory tract, or when the animal has been witnessed licking a bleeding wound.
Coagulopathies (abnormalities in blood clotting) should also be considered, especially if there is evidence of bleeding from other body sites.
Hemorrhagic gastroenteritis (HGE) is a syndrome seen in dogs whose cause is unknown. It usually causes acute diarrhea with fresh blood in it, and vomiting, hematemesis (vomiting blood), and melena can also be seen.
Any time surgery is performed on the upper gastrointestinal tract, bleeding may occur into the tract. Melena can then appear 12-72 hours after surgery. This form of melena should be very transient.
Gastrointestinal ischemia (lack of blood supply) secondary to shock, volvulus (torsion), intussusception (telescoping of the bowel into itself), or infarction (blockage of circulation to an area) can cause death of the lining of the intestines and bleeding into the intestines with subsequent melena.
Heavy metal toxicity including arsenic, lead, and zinc are uncommon causes of melena in the dog.