Maria Wiberg,     Helsinki, Finland

Etiopathogenesis

Pancreatic acinar atrophy is by far the most common reason for the clinical signs of EPI. The breeds most commonly affected with the acinar atrophy are German shepherds, rough-coated collies, and Eurasians. In these breeds, an autosomal-recessive inheritance model has been suggested. Thus far genetic studies have not been able to identify the genes involved (Clark et al, 2005; Proschowsky and Fredholm, 2007). Females and males usually are affected equally.

Studies with German shepherds and collies suggest that pancreatic atrophy is a result of an autoimmune-mediated atrophic lymphocytic pancreatitis, which gradually may lead to almost total destruction of pancreatic acinar tissue (Wiberg, Saari, and Westermarck, 2000). Typically the endocrine part of the pancreas is unaffected. A long-term follow-up study of a German shepherd litter revealed that the disease was not congenital, and a polygenic inheritance pattern has been suggested (Westermarck, Saari, and Wiberg, 2010). Genetic predisposition to the disease and the typical histologic findings during the progression of acinar atrophy have been taken as primary evidence of the autoimmune nature of the disease.

Wiberg, Saari, and Westermarck (1999b) divided the progression of acinar atrophy into subclinical and clinical phases. The subclinical phase is characterized by marked lymphocytic inflammation into a partially atrophied acinar parenchyma. Cytotoxic T cells are predominant when the tissue destruction is in progress. When the disease progresses to end-stage atrophy, the clinical phase of EPI develops. An atrophied pancreas is thin and transparent with no increase of fibrotic tissue.

The natural progression of the atrophic pancreatitis can vary markedly. Clinical signs of EPI usually appear at 1 to 5 years of age but also can be seen in older dogs. Dogs may remain in the subclinical phase for years and sometimes for life (Wiberg and Westermarck, 2002). Markers that predict which dogs are likely to develop clinical disease or environmental factors that trigger disease have not been identified thus far.

Chronic pancreatitis is the most common cause of EPI in cats and humans. In dogs, chronic pancreatitis has been recognized increasingly as a cause of EPI. Chronic pancreatitis usually affects older dogs, and breed-specific clinical and histopathologic features have been reported (Batchelor et al, 2007b; Watson et al, 2011). Unlike the situation of atrophic pancreatitis, in chronic pancreatitis usually a progressive destruction of the exocrine and endocrine pancreas is accompanied by fibrosis. Clinical signs are nonspecific gastrointestinal signs and sometimes are related to the development of diabetes mellitus. The congenital form of exocrine or exocrine and endocrine pancreatic hypoplasia sometimes is found in young puppies. EPI is reported rarely in association with pancreatic neoplasia.

Clinical Signs

Typical clinical signs of EPI include increased fecal volume and defecation frequency, yellow or gray feces, weight loss, and flatulence. Other common signs are polyphagia; poorly digested, loose, and pulpy feces; or coprophagia. Signs of nervousness or aggressiveness may occur possibly because of abdominal discomfort caused by increased intestinal gas. Severe watery diarrhea is usually only temporary. Skin disorders also have been reported. Although the signs of EPI are considered typical, they are not pathognomonic for pancreatic dysfunction, because similar maldigestion signs may be observed in other small intestinal disorders.

Diagnosis

Diagnosis of exocrine pancreatic dysfunction is based on typical clinical findings and confirmed with abnormal pancreatic function testing. Routine serum biochemistry profile and complete blood count often show unremarkable changes. Serum amylase and lipase activities are not useful in the diagnosis of EPI. Various pancreatic function tests that measure pancreatic enzymes in the blood and feces have been used to diagnose canine EPI. The diagnostic value of the tests has relied mostly on their ability to distinguish whether the clinical maldigestion signs are caused by EPI or a disease of the small intestine.