Canine
Cushing's Disease
Frequently Asked Questions
What is Cushing's Syndrome/Disease?
Cushing's syndrome
and Cushing's disease in dogs, more accurately known as
hyperadrenocorticism is the condition which occurs when
the body produces too much hormone, particularly corticosteroids
or cortisol.
What Causes Hyperadrenocorticism?
Cushing's syndrome
(~15% of all cases of spontaneous hyperadrenocorticism)
occurs as the result of a typically benign tumor of the adrenal
gland, which causes the gland to secrete excessive amounts of
cortisol.
Cushing's disease
(~85% of all cases of spontaneous hyperadrenocorticsm)
is cased by a typically benign tumor on the pituitary gland, which
in turn results in an overproduction of adrenocorticotropic hormone
(ACTH), the hormone which stimulates production of corticosteroids
by the adrenal gland. Cushing's disease is also commonly referred
to as Pituitary-Dependent Hyperadrenocorticism (PDH).
Iatrogenic Cushing's
(non-spontaneous) occurs as the result of over administration
of corticosteroids such as prednisone.
What are the Symptoms
of Cushing's?
Typical physical symptoms
include:
- Increased/excessive
drinking (polydipsia or PD)
- Increased/excessive
urination (polyuria or PU)
- Increased/excessive
appetite (polyphagia)
- enlarged, distended
abdomen
- muscle weakness
(most commonly in the back legs)
- thinning hair (alopecia--usually
evenly distributed) and lack of new hair growth
- thinning skin
- "skull-like"
appearance of head
- hyperpigmentation
of skin
- calcified skin bumps
- obesity
- chronic or frequent
infections (most notably pancreatitis, urinary tract infections,
strep throat, and staph infections)
Behavioral symptoms
include:
- lethargy/decreased
activity
- increased panting
- seeking out of cool
sleeping surfaces (bathroom tiles, etc.)
- disturbance of the
sleep/wake pattern (increased sleeping during the day, restlessness
at night)
- decreased interaction
with owners
How is Cushing's Diagnosed?
As part of a veterinarian's
examination, a complete blood count and chemistry panel may be run.
Elevated white blood cell counts (especially neutrophils), elevated
liver enzymes (particularly alkaline phosphatase), and elevated
cholesteral levels in conjunction with clinical symptoms, suggest
that Cushing's may be present and indicate a need for further, more
specific testing.
To confirm Cushing's,
a low-dose dexamethasone test may be done. As part of this test,
a blood sample is drawn to measure the baseline (or pre-test) blood
cortisol level. Next, an injection of dexamethasone is given. Four
to 8 hours later, a second blood sample is drawn to see if the dexamethasone
was able to suppress the body cortisol level. In a normal dog, dexamethasone
does suppress cortisol levels in the blood. In Cushinoid dogs, cortisol-production
suppression does not occur. Thus, a definitive diagnosis is confirmed.
Another commonly used
test is the ACTH stimulation test. In this test, ACTH--the adrenal
gland-stimulating hormone produced by the pituitary gland--is used
instead of dexamethasone.
Another less commonly
used, and less well-regarded test is the measurement of the urine
cortisol/creatinine ratio.
To confirm the type of
Cushing's present, a high-dose dexamethasone suppression test may
be run. Most dogs with pituitary tumors will have cortisol suppression
on this test. High-dose dexamethasone will have little to no effect
on an adrenal tumor.
When the results of a
high-dose dexamethasone suppression test are inconclusive (i.e.,
49-51% suppression), follow-up x-rays and/or ultrasonography can
help reveal the presence or absence of an adrenal gland tumor.
What are the Treatments
for Cushing's?
Lysodren
(o,p'-DDD or Mitotane) is the most commonly prescribed drug
for treating Cushing's Disease (Pituitary Dependent Hyperadrenocorticism).
It works by destroying the outer layer of the adrenal glands (adrenal
cortices), thus limiting their ability to produce cortisol in response
to the ACTH signals of the hyperactive pituitary gland.
Loading Dose.
Treatment begins with a "Loading Dose" of Lysodren. The
dog is given a large, daily or twice daily dose of Lysodren until
a response is seen. The typical response begins with a diminished
water intake and/or a diminished appetite, but can also include
diarrhea, vomiting, and lethargy. The typical loading period is
6 to 9 days, however, it is crucial that the owner monitor the dog's
water and food consumption and observe the dog's behavior as it
is possible for the dog to have an extreme response which requires
the intervention of a veterinarian. Often, the monitoring vet will
prescribe prednisone to keep on hand in case of an extreme reaction.
Some vets chose to administer prednisone in conjunction with Lysodren
during the loading doses, in order to fend off an adverse reaction.
Maintenance Therapy.
Lysodren therapy continues with a weekly or twice-weekly dosage
of Lysodren to keep the adrenal cortices killed back. The weekly
dosage generally begins at the same level as the daily loading dose,
but it is often adjusted as the individual dog's response to the
drug indicates.
ACTH stimulation tests
may be recommended periodically (every 3 to 6 months, generally)
to monitor the progress of Lysodren therapy.
Related
Links
Lysodren
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