Page 900 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

CHAPTER 5

LIVER DISEASE
VetBooks.ir Andy Durham 875

Domesticated equids appear to be especially This contrasts markedly with the situation in
prone to liver disease. Cases are sometimes human hepatology where the two most common
suspected on the basis of suggestive clinical causes of liver disease (excessive alcohol
signs, but frequently liver disease is first identi- consumption and obesity) can be diagnosed
fied unexpectedly when investigating horses with nothing more than the patient’s history
with mild and non-specific illness; for example, and a cursory examination. Additionally,
a subdued demeanour or poor enthusiasm for further simple tests are available to identify
exercise; or even when evaluating clinically other common causes of liver disease in humans
healthy horses during routine ‘wellness checks’. such as hepatitis viruses. The frequent inability
When investigating a horse with suspected to identify the cause of a horse’s liver disease
liver disease, the veterinarian may wish to is unfortunately a common frustration for the
answer four main questions: (1) does the horse equine veterinarian.
actually have liver disease; (2) what might
have caused the liver disease; (3) what is the CLINICAL EVALUATION OF
prognosis for the condition; and (4) what HORSES WITH LIVER DISEASE
treatment or management is appropriate for the
case? The prime clinical investigative methods A very important fundamental principle when con-
by which these questions might be addressed sidering liver disease is the distinction between a
include examination of the history and clinical horse whose liver is failing to adequately perform
signs shown by the horse; analysis of blood its usual function versus a horse with damage to the
samples; imaging of the horse’s liver; and liver that does not interfere significantly with hepatic
examination of liver biopsy specimens. Each of metabolic activities. Many organs possess a ‘reserve
these investigative options has certain strengths capacity’, which implies that a certain amount of
and weaknesses that the veterinarian should damage may occur to that organ without functional
be aware of in order to make best use of the compromise. In the case of the liver, it is estimated
diagnostic data obtained. A high success rate that approximately 60–70% of hepatic capacity may
can be achieved with confirming the presence be lost before metabolic activities are compromised.
of liver disease, establishing a prognosis and This suggests that horses presenting with evidence
selecting an appropriate therapeutic approach. of hepatic insufficiency represent a small subset of
However, the greatest investigative weakness liver disease cases with the most damaged livers.
currently exists in identifying the cause of This has two important consequences, which affect
liver disease in a horse. Although many causes the diagnostic and prognostic value of clinical signs
of liver disease are well recognised (see below in suspected hepatopathy cases. Firstly, clinically
for further discussion), few of these can be normal horses may well be suffering from exten-
definitively identified without examining biopsy sive liver disease and secondly, the presence of any
specimens. Furthermore, even when biopsy overt clinical signs of hepatic insufficiency implies a
is performed it is common for the pattern of considerable degree of liver damage with subsequent
histopathology to be non-specific for causation. prognostic relevance.