Unfortunately, we don't really know how common clinically relevant pancreatitis really is in our feline patient population. Based on necropsy studies, pancreatic inflammation may be found in anywhere from <1% to 67% of cats, which is obviously an enormous range. In addition, it is not clear that all pancreatic inflammation is clinically important. However, anecdotal evidence suggests that pancreatitis is a relatively under-diagnosed problem in the clinical patient population (which is also my opinion).
Cases of feline pancreatitis are often classified as acute, chronic, or chronic active based primarily on histopathologic findings. Acute pancreatitis is generally characterized by neutrophilic inflammation or necrosis without evidence of permanent structural changes. The chronic form is characterized by predominantly lymphocytic inflammation and permanent changes such as fibrosis and atrophy. and I actually do use this scheme as well. When characteristics of both are present, the term chronic active pancreatitis is often used.It is still not clear whether these different classifications reflect different eitiologic origins, or are different phases of one disease process. Actually, no specific underlying cause is identified in a majority of feline pancreatitis cases, regardless of type. Infectious diseases such as Toxoplasma, and certain fluke infestations have been implicated in some cases. It is also likely that some of the risk factors important for people and dogs, such as trauma, ischemia, or certain medications would also be important in cats. One key difference between cats and other species is that there does not seem to be a clear association between dietary fat content or inherent lipid disorders and development of pancreatitis.
There is an association between feline pancreatitis, inflammatory bowel disease, and cholangitis (+/- hepatic lipidosis), but no specific cause & effect relationship has been worked out. Nonetheless, cats with either IBD or cholangitis should be considered at risk for development of pancreatitis. Also, because these conditions are such common co-morbidities, and because they do have significant implications for therapeutic management, any diagnostic plan for feline pancreatitis should also take these diseases into account.
One of the things that makes feline pancreatitis such an enigma is that there are no particularly characteristic or specific clinical signs and the clinical course can range from mild and subclinical to severe and life threatening. In general, chronic pancreatitis is more likely to present with a waxing and waning course of relatively mild clinical signs whereas acute pancreatitis is more likely to be associated with moderate to severe clinical disease.
It appears that cats of any age breed or sex can be affected and unlike dogs, cats are as likely to be underweight as overweight. The most common clinical signs identified are also non-specific, including partial or complete anorexia, lethargy, and dehydration. Other clinical signs or physical examination abnormalities that may be present include vomiting, weight loss, abdominal pain, hypothermia, diarrhea, tachypnea or dyspnea, icterus, or a cranial abdominal mass. While vomiting and abdominal pain are reported to occur much less frequently in cats with pancreatitis compared to dogs, there is certainly a valid concern that abdominal pain in cats has been unrecognized or under-reported in the past. In very severe cases, there may be evidence of a severe systemic inflammatory response which could include evidence of hemostatic disturbances, shock, or even multiple organ failure.