Gastrointestinal ulceration is the result of factors that alter, damage, or overwhelm the normal defense and normal repair mechanisms of the gastrointestinal mucosal (lining) barrier. There is no predilection for a particular age group or breed, and signs can be extremely variable from patient to patient. Some patients may have no clinical signs, while others may be in immediate need of intensive support and hospitalization, including blood transfusions.

There are many causes of gastrointestinal ulceration that range from drugs to tumors. It is important to realize that while some cases of ulceration are clear cut when reviewing the history, physical examination, and diagnostic findings, such as in the case of high dose aspirin administration in a dog with severe arthritis, others are more difficult to determine.

There are many diseases and disorders that cause similar clinical signs to patients with gastrointestinal ulceration, including:

The ingestion of certain drugs and medications may either cause gastrointestinal ulceration or signs similar to individuals with ulceration, including vomiting and lack of appetite.

Metabolic disorders like kidney failure, liver disease and hypoadrenocorticism are often associated with gastrointestinal ulceration.

Stress, pain, fear or major medical illness to include shock, hypotension (low blood pressure), trauma, and major surgery can all be associated with gastrointestinal ulceration.

Dietary indiscretion, or the ingestion of foreign bodies, is a common disorder seen in dogs. Vomiting, diarrhea, and gastric ulceration are commonly seen.

Pancreatitis is an inflammation of the pancreas, and in certain cases, can be life-threatening. The most common clinical signs seen with pancreatitis are vomiting and lack of appetite. Pancreatitis can result in GI ulceration.

Intestinal obstruction or blockage secondary to foreign bodies or tumors must be differentiated from and can cause GI ulceration. Mast cell tumors, cancer of the liver, and gastrin-secreting tumors of the pancreas should be considered.

Infiltrative diseases of the gastrointestinal tract, which are microscopic diseases that penetrate and spread throughout, including inflammatory bowel disease and lymphosarcoma (cancer) must be ruled out.

Hemorrhagic gastroenteritis is a syndrome of unknown cause seen in dogs. These animals often experience vomiting with or without blood and bloody diarrhea. Hemorrhagic gastroenteritis is most often seen in urban settings in small breed dogs.

Clotting disorders, such as thrombocytopenia (decreased platelet count) or warfarin toxicity (rat poison), may have bloody diarrhea or vomiting.

Neurologic disorders, especially of the vestibular center for balance and coordination will often experience vomiting.

Certain toxins such as lead can cause severe gastrointestinal signs and ulceration.