Exocrine pancreatic insufficiency (EPI) is most often caused by pancreatic acinar atrophy (a shrinking of the enzyme producing cells of the pancreas) the cause of which is unknown. It is seen most commonly in young dogs, especially German shepherd dogs.

EPI can have major impact on the animal because severe longstanding diarrhea and profound weight loss are commonly observed. Other medical problems can lead to symptoms similar to those encountered in EPI. These conditions should be excluded before establishing a definitive diagnosis of EPI:

Bacterial infectious diseases, such as Salmonella, Clostridium and Campylobacter.

Viruses, such as Coronavirus and Parvovirus.

Fungal infections, such as Histoplasma, Mycobacteria and Phycomyces

Parasitic disease, such as roundworms, hookworms and whipworms

Protozoal infections, such as Coccidia, Giardia and Trichomonas

Inflammatory Bowel Disease (IBD). The cause of IBD is unknown, but it is thought to be immune-mediated. Diarrhea and weight loss are commonly observed in dogs with IBD. An intestinal biopsy is the only way to diagnose IBD definitively.

Dietary intolerance or dietary allergy usually occurs in response to a particular dietary protein, but can occur secondary to almost any component in the animal's food. Diarrhea and abnormalities of the skin are most commonly seen with this disorder.

Drugs and toxins are more often associated with acute diarrhea, but chronic exposure to certain medications or toxins can be associated with chronic diarrhea.

Cancer of the gastrointestinal tract can cause diarrhea and weight loss.

Obstruction (blockage) of the gastrointestinal tract due to cancer, foreign bodies, intussusception (telescoping of the bowel onto itself), or stricture can be associated with chronic diarrhea.

Metabolic disorders including kidney and liver failure, diabetes mellitus and hypoadrenocorticism (Addison's disease) may be associated with weight loss and diarrhea.

Duodenal ulcers can cause diarrhea and melena (black tarry stools secondary to the presence of digested blood).

Small intestinal bacterial overgrowth is characterized by an overgrowth of normal intestinal bacterial flora and may be associated with chronic diarrhea.

Lymphangiectasia is a chronic protein-losing disorder of the intestinal tract that is associated with chronic diarrhea.

Short bowel syndrome may develop after a large portion of the intestinal tract has been removed surgically. Chronic diarrhea may be observed in this syndrome.

Gluten-sensitive enteropathy is an intestinal disorder seen most commonly in Irish Setters. It is an inflammatory disease that occurs in response to diets containing gluten (a protein of wheat).

Irritable bowel syndrome (spastic colon) is a chronic intermittent disorder that is associated with diarrhea, abdominal pain and gas.