Intestinal cancer (lymphosarcoma, carcinoma)
Chronic foreign bodies
Ulcers
Intussusception
Haemorrhagic enteritis
Intestinal parasites (worms, coccidia)
Immune-mediated (food allergy, autoimmune diseases)

The main gut related signs are diarrhea and less commonly vomting

Conditions not originating in the gut include

Congestive heart failure
Constrictive pericarditis
Lymphatic disorders

The additional clinical signs will depend largely on the cause of the problem, but may often include:
Lethargy-tired, lacks the energy the animal normally displays
Weight loss
Ascites-swollen abdomen (belly) due to fluid accumulation.
Respiratory difficulty-problems breathing
Dependent oedema-accumulation of fluid in tissues, especially the lower parts of the body.

Diagnosis can be difficult and is focused on identifying the underlying causes. Tests include
blood samples to assess organ function and measure blood protein levels.
Faecal examination to look for parasites and the presence of undigested fats and sugars.
Radiography-( X-rays) and ultrasound of the chest and abdomen to assess the heart, lungs and abdominal organs.
Endoscopy-a fibre-optics tube is passed into the from the mouth stomach to allow the inside of the stomach to be visualized. This equiptment also allows samples of an suspect area os the stomach wall be collected for analysis.
Laparotomy- exploratory surgery in the abdomen. This is often a very practical means of looking directly at the GIT and collect samples of sections of the intestine for histopathyology (examination under a microscope) to establish the cause of PLE.

Treatments are aimed at the cause, however initial treatment may begin with changing to a simplified diet.