Faculty of Veterinary Science, The University of Melbourne, Werribee, VIC, Australia
Dogs with acute pancreatitis generally present with a sudden onset of anorexia, abdominal pain and vomiting, and variable amount of abdominal effusion. The onset of pancreatic inflammation and/or necrosis can initiate a number of inflammatory pathways, which may progress to cause hypovolaemia, systemic inflammatory response syndrome (SIRS), or multiple organ dysfunction.1 Even in very severe cases the clinical signs of acute pancreatitis in dogs are not pathognomonic. It is essential therefore to ensure that differential diagnoses for acute pancreatitis such as intestinal obstruction, closed pyometron or septic peritonitis that are all life-threatening and require surgical intervention, are eliminated as a priority. The next essential step is to eliminate metabolic causes of vomiting that require specific intervention. A typical diagnostic algorithm for acute pancreatitis is shown at the end of this manuscript, as adapted from Mansfield.2
None of the changes seen on routine clinical pathology are specific for pancreatitis, but are useful in aiding in the diagnostic pathway. Some dogs may have overt lipaemia, which does increase the index of suspicion for pancreatitis. There have been a number of recent studies and new diagnostic modalities that have investigated pancreas-specific blood tests. Although some of these are highly specific and sensitive, it is important to remember that the pancreas is highly susceptible to disease within the abdomen. That means that although pancreatic inflammation is present on histology, pancreatitis is not the reason why the animal is presenting.3
Serum lipase and amylase concentrations have been shown to increase in experimental and naturally occurring canine pancreatitis.4-6 However, neither enzyme is specific to the pancreas as they also originate from gastrointestinal mucosa and are excreted by the kidneys. Conversely, serum lipase and amylase concentrations can also be normal in dogs that do have pancreatitis. Canine pancreatic lipase measures lipase that originates solely in the pancreas. The canine pancreatic-lipase immunoreactivity (cPLI) assay was developed into a commercially available specific canine pancreatic lipase (spec-CPL) sandwich ELISA, with results < 200 µg/L expected in healthy dogs, and results > 400 µg/L considered consistent with a diagnosis of pancreatitis.7 A new in-clinic rapid semiquantitative assay (SNAP-cPL; IDEXX Laboratories) has also been developed. The reported sensitivity of spec-cPL for diagnosing pancreatic inflammation in dogs ranges from 21 to 88%.8-12 The sensitivity of pancreatic lipase is greatly increased when more severely affected dogs are assessed. Specificity of pancreatic lipase has been reported to range from to 80% to 97.5%.9,11-13 In summary, a negative result for SNAP-cPL or cPLI means it is likely that the dog has disease other than acute pancreatitis. A positive result still requires confirmation and elimination of other disease by some other modality.
Pancreatic elastase (PE-1) is released immediately after trypsin activation and also plays a role in perpetuating inflammation. The current commercially available canine PE-1 (cPE-1) assay is an ELISA (ScheBo®.Elastase 1-Canine, ScheBo®.Biotech AG, Netanyastrasse 3, D-35394, Giessen, Germany). This assay appears to have a high positive likelihood ratio and low negative likelihood ratio.
Diagnostic imaging is a vital component of the diagnostic workup for dogs with possible pancreatitis. The radiological findings in acute pancreatitis are not particularly sensitive. Signs that may be apparent include decreased contrast and lack of detail in the cranial abdomen due to the surrounding peritonitis. Despite this limitation, abdominal radiography is still an important part of the diagnostic workup to rule in or rule out intestinal obstruction or other changes such as free gas within the abdomen or a distended uterus. Abdominal ultrasound is increasingly performed in general practice and aids substantially in the diagnosis of acute pancreatitis in dogs. Changes in pancreatic echogenicity and development of focal lesions can be detected. Acute necrotizing pancreatitis is frequently associated with an enlarged, hypoechoic pancreas and peripancreatic necrosis (manifested as hyperechogenicity surrounding the pancreas). It is extremely difficult to elucidate sensitivity or specificity of ultrasound, as it is both operator and equipment dependent. Certainly, ultrasound cannot distinguish between inflammation, necrosis or neoplasia.
In summary, no single noninvasive diagnostic test is 100% sensitive or specific for acute pancreatitis. A logical and systematic evaluation is required in every individual dog to ensure an accurate diagnosis.
References
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