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        Islet Cell Tumor in the Ferret
 
        Islet cell tumors, also known as insulinomas, are the most common
neoplasm in the ferret, based on the frequency of surgical and autopsy
submissions at the Armed Forces Institute of Pathology.  Over a period of two
and a half years, this neoplasm alone has accounted for almost 15% of all ferret
submissions.
 
        Islet cell tumors derive their name from their cell of origin.  These
neoplasms arise in the "islets of Langerhans" - a group of special cells in the
pancreas which produce insulin (also giving rise to the term insulinoma).
Insulin is a hormone which allows most of the cells in the body to utilize the
glucose in the blood.  The excess levels of insulin produced by these tumors
drive the glucose in the blood into the cells of the body, causing a dangerously
low blood glucose level, known as hypoglycemia.  (In diabetes, the opposite is
true - low levels of insulin production render the animal's cells unable to use
glucose, and dangerous hyperglycemia results).
 
        Not all islet cell tumors appear to be functional, however.  Islet cell
tumors are often found as incidental findings at autopsy of animals dying of
unrelated causes.  Finally, a small percentage of animals fail to show
characteristic signs of hypoglycemia, or show signs that are so subtle that they
are not noticed by the owner and picked up on routine blood screening for other
conditions.
 
        Hypoglycemic ferrets may exhibit a wide range of clinical signs.  Weight
loss appears to be a common finding in affected animals, and is occasionally the
only sign.  This is an excellent reason why you should periodically weigh your
pet as part of a good preventive health program.  Signs that are more diagnostic
of islet cell tumors are episodic depression and lethargy, which in some animals
manifests as stupor (apparent loss of touch with its surroundings), salivation,
difficulty in using the hindlegs, vocalization, and in cases of severe
hypoglycemia, seizures.
 
        Diagnosis of islet cell tumors is fairly simple and consists primarily
of measuring the blood glucose levels in the ferret, which your vet can do if
you suspected this problem. (Some vets additionally measure insulin levels, but
in most cases, this is unnecessary and wastes valuable time.)   Animals with
blood glucose levels less than 60 mg/dl should be strongly suspect of having one
or more of these tumors. Exploratory surgery in hypoglycemic but otherwise
healthy ferrets should be scheduled at the earliest possible time.
 
        In animals where surgery is not an option, or until such a time as
surgery is possible, medical management may be attempted by using a combination
of prednisone (which raises blood glucose levels by mobilizing carbohydrate
stores) and diazoxide (Proglycemr) an antihypertensive drug which appears to
decrease islet cell secretion of insulin.  It is important to realize that this
is only a temporary measure and rarely is effective in controlling the animal's
hypoglycemia for a long period..
 
        It is also important to note that in a large number of cases (5/6 in one
study), ferrets that had islet cell tumors surgically removed developed a second
or more tumors at a later date. (Additionally, make sure that your veterinarian,
if surgery is performed, takes a moment to check the adrenal glands for those
extremely common proliferative lesions we so often see in ferrets.)
 
        If you have a several ferrets, it is extremely likely that one of them,
sometime during its life, will develop an islet cell tumor; it's the "nature of
the beast".  Just watch them closely for the clinical signs that I have
described, and have your vet check them if you have even the slightest
indication of a problem.
 
 
Happy ferreting!!!
 
Bruce Williams, DVM
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1.  Marini, RP et al.  Functional islet cell tumr in six ferrets.  JAVMA 202(3)
430-432, 1993.
 
2.  Kawasaki, TA  Personal communication.
 
[Posted in FML issue 0635]