Classification of feline inflammatory liver disease(s)
Inflammatory disease has been reported to be the second most common category of liver disease in cats in the US (after hepatic
lipidosis). However, within this category, there are a number of different pathologic patterns that may represent different
stages of disease or even potentially separate disease conditions. This has resulted in considerable confusion about whether
these various conditions should be lumped together in a broad category (cholangitis), or whether subtypes of inflammatory
disease could be separated out to provide more specific and individualized information about etiology, diagnostic testing,
therapeutic options, and prognosis.
Recently, the World Small Animal Veterinary Association (WSAVA) sponsored an international group of pathologists and clinicians
tasked with standardizing histopathologic classification of liver disease in small animals. Among the recommendations of
the WSAVA Liver Standardization Group (LSG) was that the term cholangitis be used in preference to cholangiohepatitis in cats.
This recommendation was made because although inflammatory changes may occasionally extend into the hepatic parenchyma, the
primary inflammatory changes are typically centered around the bile ducts. This is in contrast to dogs, in which the primary
inflammatory liver disease, chronic hepatitis, directly involves the parenchyma.
Under the category of cholangitis, The WSAVA LSG recognizes three distinct forms: neutrophilic, lymphocytic, and fluke-associated.
Of course, in clinical practice it can't be quite that simple. Although there are now criteria for separating these three
categories based on histopathology, there is significant overlap in the clinical presentation and results from common clinical
tests. There is also a further division of the neutrophilic form into acute and chronic forms (thought to represent different
ends of a spectrum or progression of a single disease). Finally, there is a separate entity called lymphocytic portal hepatitis
which has unknown clinical significance. Even though this scheme is not as simple as we might wish, it is still an improvement
over the old system of just calling everything cholangiohepatitis. A roughly outlined comparison of the subcategories of
cholangitis is presented in Table 1.
Table 1. Characteristics of different forms of feline cholangitis