Insulinoma and diabetes cause the opposite results, both from problems
with the pancreas.  In untreated diabetes there winds up being too much
sugar in the blood stream and insulin is given (and sugars if there winds
up being too much insulin given which is what you were thinking of)
whereas in insulinoma there start being tumors of a type which do not
respond to the blood glucose levels and which constantly pump out large
amounts of insulin.  The common symptoms (from tiredness to fully out of
it grande mal seizures to death) happen because the brain isn't getting
enough sugar.  There is a hypothesis that has some weight behind it
(though it is still a hypothesis) that too much starch and sugar in the
diet may lead to the formation of these growths.  Also, removing them
from the diet early on helps many ferrets (but not all) go longer with
surgery or meds.  It is important to see which works best for a given
individual.  In the last stages of insulinoma when the islet cell tumors
have taken over much of the pancreas or suppressed much of it, or both
then when meds no longer work at their highest levels adding sugars to
the diet can sometimes give as long as a few extra good quality months.
The meds used are Pred (usually Prednisolone because it skips the liver
processing step needed by Prednisone so it is often more effective), and
Diazoxide.  When caught late it can be counted on to return.  If caught
early it returns in about 40% of the individuals within 10 months as per
vet pathologist Dr. Bruce Williams.  It almost never metastasizes to
other organs (the hallmark of malignancy is the ability to show up in
DISTANT organs).  Blood sugar in ferrets can be dropped by other things
as well, but much more rarely.  Some examples include carcinoma (Been
there once.), lymphoma (Been there once.), sepsis (Been there once.),
inability to get enough nutrition due to a severe GI disease (Been there
a few times.).  Amazing what you encounter and learn in 23 years...
 
No, never give insulin to a ferret with active insulinoma because there
is already too much naturally produced insulin present.
 
I suggest reading the write up at
http://www.afip.org/ferrets/index.html
 
Diabetes is much more rare and sometimes occurs temporarily after
insulinoma surgery till the suppressed tissues become active again.  That
is usually very short term.  On very rare occasions there are ferrets
with permanent diabetes for whatever reason which is one reason if a
ferret is out of it to test rather than just start meds.
 
For diabetes info I suggest
http://fhl.sonic-weasel.org (ALWAYS  A GREAT PLACE FOR ALMOST ANY TYPE
OF HEALTH INFO)
 
For both also go to
http://www.miamiferret.org
 
Either can be fatal, but there are approaches to use which are
exceedingly valuable.
[Posted in FML issue 4572]