Vomiting cats: Diagnostic clues (Proceedings)

Aug 01, 2009

Vomiting is a common and frequently complex problem in cats. Adult cats often have different and more chronic causes of vomiting than kittens, but the condition remains a common reason for cats to be presented to veterinarians for care. Vomiting can be caused by both primary gastrointestinal diseases (e.g. infectious, inflammatory, parasitic, anatomic (obstructive, trichobezoars), drug-related or nutritional) and by extra-gastrointestinal (GI) diseases, such as endocrinopathies (e.g. hyperthyroidism), metabolic disease (e.g. renal failure), inflammatory or other liver diseases, pancreatitis, and neoplasia (especially alimentary lymphoma). This wide spectrum of potential causes of vomiting in cats increases the difficulty for the practitioner in making a definitive diagnosis. Nevertheless, it is important to carefully consider each of the potential differentials to prevent the problem from progressing to create further clinical deterioration.

Extra-gastrointestinal causes of vomiting

One of the first steps in evaluating a vomiting cat is to attempt to determine as quickly as possible, whether the vomiting is due to a primary gastrointestinal problem (e.g. gastritis, IBD, etc), or caused by a disease outside of the gastrointestinal tract (e.g. liver or renal disease, pancreatitis, endocrinopathies, heartworm, etc). In many cases of vomiting due to gastrointestinal disease, the diagnosis is made by imaging, evaluation of tests of GI function, or biopsy of the GI tract. However, in extra-GI causes of vomiting, laboratory tests are more important to determining the cause of the problem (e.g. thyroxine levels for hyperthyroidism, chemistry panel for renal or liver disease, etc). The best way to help point the clinician toward the proper diagnostic approach is to obtain a thorough history of the problem and perform a complete physical examination. These tools of the medical trade are often underestimated in their importance, but can be invaluable to the clinician in helping to refine and focus the diagnostic approach.

Feline pancreatitis

Feline pancreatitis is a very difficult disease to definitively diagnose antemortem (especially chronic cases or in cats that only vomiting occasionally or intermittently). This partly due to the lack of specific clinical signs in cats, as well as the lack of a rapidly available test for diagnosis of the disease. In cats with chronic pancreatitis, the available tests are even less sensitive and specific, thus diagnosis is even more very difficult.

The clinical signs of feline pancreatitis can be quite different from those in dogs. Acute pancreatitis is frequently encountered in obese dogs fed a high fat diet, while cats are more likely to be underweight, and high fat diets do not appear to be an important predisposing factor. Cats of all ages, sexes and breeds are affected, although Siamese cats are reported to have pancreatitis more frequently. Finally the clinical signs of pancreatitis in cats are very vague, with the most common signs being lethargy (reported in 100% of cats in one study), anorexia, dehydration and abnormal body temperature (either fever or hypothermia can be observed. Thus, the clinical signs may be quite variable, and this must be taken into consideration with each patient.

The fTLI was developed many years ago as the definitive test for diagnosis of exocrine pancreatic insufficiency, and the data and follow up have confirmed its utility for this condition. In recent years, others have evaluated the fTLI as a diagnostic test for acute pancreatitis – working on the premise than an elevation in serum concentrations were consistent with pancreatic leakage or inflammation. While an increase in fTLI can be found in cats with acute pancreatitis, a normal fTLI does not rule out pancreatitis. This is because the leakage of enzymes tends to decrease rapidly following an event, or the enzymes are inactivated and scavenged by the body's peptidases (macroglobulin, etc) within12-24 hours following an acute insult. Further, in chronic or low grade pancreatitis, the leakage is not great enough to be detected by this assay. Thus, while an increase in fTLI is specific for pancreatic enzyme leakage, it is not sensitive enough to be a definitive test for pancreatitis. More recently, an ELISA for pancreatic specific lipase (feline pancreatic lipase immunoreactivity –fPLI) was developed by the GI lab at Texas A&M University. The assay is species specific, has been used to detect elevations in pancreatic lipase in clinical cases, and appeared to be more specific and sensitive for diagnosis of pancreatitis in cats than fTLI. However, the assay had a relatively low sensitivity (33%) and specificity (<80%) when a cut off value of 100 ug/L was used for diagnosis. To improve upon this assay, a radioimmunoassay (RIA) was developed and validated in 30 healthy cats. In a recent paper, the sensitivity and specificity of this assay was tested in cats with mild pancreatitis and in cats with moderate to severe pancreatitis. The sensitivity in mild pancreatitis was found to be 80% while the specificity in healthy cats 75%. However, in severe pancreatitis (determined by pancreatic biopsy) the sensitivity and specificity were both 100%. These findings underscore the utility of this test in cats with acute pancreatitis, however, there still is a problem with detection of low grade or chronic pancreatic inflammation in cats with this assay. In cats with chronic pancreatitis it will still be necessary to evaluate the combined historical, physical exam, lab data and imaging information along with the fPLI when making a diagnosis.

Imaging studies are frequently used to help identify cats with acute pancreatitis, however, the changes are not consistent and can be particularly subject to interpretation and operator expertise. The most common radiographic abnormalities include a generalized or focal (upper right quadrant) loss of peritoneal detail (suggesting peritonitis or peritoneal effusion), presence of a mass in the area of the pancreas, hepatomegaly, dilated intestinal loops, or a fluid-filled duodenum. However, these findings are not specific for pancreatitis, and the sensitivity of radiography for diagnosing pancreatitis is low in cats. Ultrasonography may reveal a hypoechoic pancreas, hyperechoic mesentery, a mass effect, a dilated common bile duct or it may be normal. In previous studies, the sensitivity of ultrasound for diagnosis of pancreatitis was reported to be 24%. In a recent study, mild pancreatitis was still shown to be difficult to diagnose via abdominal ultrasound. However, in that same study, ultrasound had an 80% sensitivity and 88% specificity in cats with moderate to severe pancreatitis. The most reliable method for making an accurate diagnosis of pancreatic disease remains direct visualization and histopathology. However, this can be expensive, increase the risk of complications (anesthesia/surgery), and in cases with focal lesions, which is common with chronic pancreatitis, the lesions may be missed on visual or histopathologic inspection.