Cushing's Disease
This information is not meant to be a substitute for veterinary care.
Always follow the instructions provided by your veterinarian.
Cushing's disease (hyperadrenocorticism) is the overproduction of the
hormone cortisol by the adrenal glands that are located in the belly near
the kidneys. Cushing's disease occurs commonly in dogs, but is rare in cats.
Most dogs with Cushing’s disease are about 6 years old or older but
sometimes Cushing's disease occurs in younger dogs. Cortisol affects the
function of many organs in the body, so the signs of Cushing’s disease may
be varied. Some of the more common signs of Cushing’s disease include hair
loss, pot-bellied appearance, increased appetite, and increased drinking and
urination called polydipsia and polyuria (PU/PD). Hair loss caused by
Cushing’s disease occurs primarily on the body, sparing the head and legs.
The skin is not usually itchy as it is with other skin diseases. If you pick
up a fold of skin on a dog with Cushing’s disease, you may notice that the
skin is thinner than normal. The pet may have fragile blood vessels and may
bruise easily.
Less common signs of Cushing’s disease are weakness, panting, and an
abnormal way of walking (stiff or standing or walking with the paws
knuckled over). Some dogs with Cushing’s disease develop a blood clot to
the lungs and show a rapid onset of difficulty breathing.
Dogs that are given prednisone or similar drugs can develop signs that
look like Cushing’s disease (called iatrogenic Cushing’s).
There are two types of Cushing’s disease that are treated differently.
The most common form of Cushing’s disease is caused by the overproduction of
a hormone by the pituitary gland in the brain that in turn controls the
amount of cortisol produced by the adrenal glands. This is called
pituitary-dependent Cushing’s. A small percentage of dogs with Cushing’s
disease have a tumor of one of the adrenal glands which is called
adrenal-dependent Cushing’s.
There is no single test to diagnose Cushing’s disease. The history,
physical exam, and results of initial blood and urine tests often provide a
strong suspicion for the presence of Cushing’s disease. Laboratory tests
that are most commonly altered by Cushing’s disease are an increase in white
blood cell count, increase in the liver enzyme ALP (also called SAP or serum
alkaline phosphatase), increased blood sugar (although not as high as the
blood sugar levels of
diabetic patients), increased cholesterol and
dilute urine. See
What Do Those Lab Tests Mean? for additional
information about laboratory tests.
The large amount of cortisol in the body suppresses the immune system and
allows the pet with Cushing’s disease to get bacterial infections. The most
common location for infection is the bladder. Pets with Cushing’s disease
may have a silent bladder infection meaning they don’t show signs of having
the infection such as straining to urinate. A culture of the urine may be
necessary to diagnose the infection.
X-rays of the belly often show a large liver. Occasionally the x-ray will
show calcium in the area of one of the adrenal glands that is suggestive of
an adrenal tumor. Ultrasound of the belly may show enlargement of both
adrenal glands in pets with pituitary-dependent Cushing’s or enlargement of
just one of the adrenal glands in pets with an adrenal tumor. The adrenal
glands are NOT always seen during an ultrasound exam in pets with Cushing’s.
In some pets with an adrenal tumor, the tumor can be seen growing into large
blood vessels close to the adrenal gland or spread from the tumor may be
seen in the liver.
Specific tests for Cushing’s disease are performed to confirm the
diagnosis and to determine the type of Cushing’s disease that is present,
pituitary-dependent, or adrenal-dependent. Specific tests for Cushing’s
disease have varied results. In some cases the results are clear cut and the
diagnosis is made, but in other cases the test results are not clear cut and
a series of tests must be performed. Some of the specific tests for
Cushing’s disease include urine cortisol/creatinine ratio, low dose
dexamethasone suppression test, high dose dexamethasone suppression test,
and an ACTH stimulation test.
The treatment of the most common type of Cushing’s disease
(pituitary-dependent) is lifelong oral medication. The most common drugs
used to treat Cushing’s disease are o, p’-DDD (also called Lysodren or
mitotane) and Trilostane. Occasionally ketoconazole or L-Deprenyl are
used to treat Cushing’s disease but are less effective than Trilostane
or Mitotane. o, p’-DDD is initially given daily or twice
daily for about a week (sometimes more, sometimes less). The initial
treatment is called induction. o, p’-DDD can have serious side effects, so
pets being treated for Cushing’s disease must be closely watched. After
induction o, p’-DDD is given less often, usually once or twice weekly for
the life of the pet. Some pets will have a recurrence of signs of Cushing's
disease later in life, even though they are receiving o, p’-DDD. Trilostane tends to have fewer side effects than o, p’-DDD but is more expensive. Discuss with your veterinarian which treatment is best for your pet.
Treatment of adrenal dependent Cushing’s
disease is by surgical removal of the
cancerous adrenal gland. Adrenal gland
tumors can spread to other parts of the
body in which case all the cancer cannot
be removed by surgery. Medical treatment
may be given before surgery to reduce
hormone levels before surgery. o, p’-DDD is not as effective in reducing
signs in pets with adrenal-dependent Cushing’s disease as it is in pets with
pituitary-dependent Cushing’s disease. Trilostane may be effective in
controlling the signs of Cushing's in some dogs with adrenal tumors.
The prognosis for pituitary-dependent Cushing’s disease with treatment is
usually good. Some signs will disappear quickly and others gradually.
Appetite and water consumption usually return to normal in a few weeks where
as full return of the fur may take several months.
Washington State University assumes no liability for injury to you
or your pet incurred by following these descriptions or procedures.
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