Page 612 - Small Animal Internal Medicine, 6th Edition

584 PART IV Hepatobiliary and Exocrine Pancreatic Disorders

CHAPTER 36
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Hepatobiliary Diseases

in the Dog

GENERAL CONSIDERATIONS nothing about temporal chronicity, but this is impossible to
judge because many dogs with chronic hepatitis have few or
There are marked differences between dogs and cats in the no clinical signs before biopsy, and elevated liver enzymes
causes, types, and presentations of liver disease (see Table are often not detected unless a blood sample is taken for
35.2). In dogs, chronic liver disease is more common than another reason such as preanesthetic check.
acute disease and, notably, chronic parenchymal disease Chronic hepatitis is common in dogs and shows some
(chronic hepatitis) is much more common in dogs than in noticeable breed predilections, suggesting a genetic basis to
cats; it almost invariably leads to progressive fibrosis and the disease. Box 36.1 lists dog breeds reported to have a high
cirrhosis. This contrasts with cats, in which primary biliary prevalence of chronic hepatitis, and Box 36.2 lists possible
tract disease is more common but fibrosis and cirrhosis are causes for genetic increases in susceptibility, all of which
extremely uncommon. The clinical signs of liver disease in have been demonstrated in humans with chronic hepatitis
dogs therefore tend to be even more nonspecific than in cats. and some of which have been recognized in other diseases
Jaundice is less commonly associated with parenchymal in dogs. The only one that has been confirmed as a cause of
disease and, because of the enormous reserve capacity of the chronic hepatitis in dogs is the mutation of a gene involved
liver, signs may not be evident until 75% of the liver mass is in metal storage in dogs with copper storage disease (see
lost. The cause of chronic hepatitis in dogs is usually later). The others have been suspected but not proven,
unknown, with a few notable exceptions, and treatment although increases in major histocompatibility complex
focuses on attempting to slow progression of the disease and (MHC) class II antigen haplotypes in some breeds suggest
treating the clinical signs. Dogs with chronic hepatitis often genetic susceptibility to autoimmune disease (see later).
develop portal hypertension, and treatment of the associated Young to middle-aged dogs are most commonly affected,
complications is central to treatment of disease in dogs, and the sex ratio varies among breeds. Dalmatians, Dober-
whereas portal hypertension is very uncommon in cats. Both man Pinschers, and English Springer Spaniels with chronic
congenital and acquired portosystemic shunts (PSSs) are hepatitis are typically younger than Labrador Retrievers,
more commonly recognized in dogs than in cats; in addition, English Cocker Spaniels, and Cairn Terriers. It should also
vacuolar and secondary hepatopathies are very common in be noted that there are some notable geographic differences
dogs and can be confused with primary liver disease on in breed-related liver diseases, which likely reflect differences
presentation. The most common primary and secondary in breeding in different countries; diseases common in the
liver diseases in dogs are outlined in Table 36.1. United States may be unusual in the United Kingdom, and
vice versa. It is also important to remember that chronic
CHRONIC HEPATITIS hepatitis can affect mixed-breed and purebred dogs, and that
recognition of one cause in a breed does not necessarily
Chronic hepatitis is predominantly a histologic definition. It mean that chronic hepatitis in all dogs of that breed has the
is essential to take a liver biopsy before making a diagnosis of same cause. For example, in many Doberman Pinschers and
chronic hepatitis in dogs, because reactive (secondary) hepa- West Highland White Terriers, chronic hepatitis is caused by
topathy is much more common than primary liver disease copper accumulation, but in others it is not. In many cases
in this species (see later). Chronic hepatitis is defined by the of canine chronic hepatitis, the cause is unknown. This con-
World Small Animal Veterinary Association (WSAVA) Liver trasts with the situation in humans, in whom most cases of
Standardization Group as being characterized by hepatocel- chronic hepatitis are viral and some have defined and often
lular apoptosis or necrosis, a variable mononuclear or mixed effective treatments that can reverse the disease process. In
inflammatory cell infiltrate, regeneration, and fibrosis (Van dogs, chronic viral causes have not been convincingly dem-
den Ingh et al., 2006; Fig. 36.1). The histologic definition says onstrated, but the histology in some cases is suggestive of this

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