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Cushing's Disease Affects Dogs, Cats, as Well as People

Pet Column for the week of March 17, 1997

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Joseph Hahn
Information Specialist

Cushing's disease, or hyperadrenocorticism, is caused by an excess of cortisol in the body.
It is relatively rare in people, affecting between 10 and 15 of every million people each
year. The problem occurs more commonly in the dog than in the cat.

"Cushing's disease commonly affects middle-aged to older dogs," says Dr. Jennifer Brinson,
a veterinarian specializing in internal medicine at the University of Illinois College of
Veterinary Medicine Teaching Hospital at Urbana. "It is most commonly seen in poodles,
dachshunds, terriers, German shepherds, and golden retrievers.

"These animals typically present with symmetrical hair loss; excessive eating, drinking, and
urination; lethargy; and a distended abdomen," she says. "They commonly have other skin
abnormalities and secondary urinary tract infections as well."

There are three types of Cushing's disease: adrenal cortical tumor, pituitary tumor, and
iatrogenic (veterinarian-induced).

An adrenal cortical tumor--a tumor of the cortisol-producing cells of the adrenal
gland--causes excess production of cortisol. Although there are two adrenal glands, these
tumors generally develop in one gland and will lead to one abnormally large adrenal gland
and one abnormally small gland.

Pituitary-dependent hyperadrenocorticism is due to microtumors in the pituitary gland in the
brain that produce excessive amounts of a hormone that causes the adrenal glands to
produce cortisol. In this form, both adrenal glands are enlarged.

Iatrogenic Cushing's is produced by an excess of cortisol being given to a pet by a
veterinarian, for example, to treat a skin disorder. The excess cortisol in the body signals
the adrenal glands to decrease their normal production of cortisol, leading to a decrease in
the size of the adrenal glands.

Cushing's disease is first suspected with clinical signs, physical exam abnormalities, and
blood tests that are suggestive of this disease. A definitive diagnosis is made using
three-stage testing of adrenal challenge gland function.

"The treatment for an adrenal tumor is surgical removal and supplementation of cortisol until
the shrunken adrenal gland returns to normal function," says Dr. Brinson. "It is uncommon
for these tumors to recur on the remaining adrenal gland.

"The treatment for pituitary-dependent Cushing's is generally Mitotane® (O,P'-DDD), a
chemical derivative of the pesticide DDT," she says. "This drug destroys the zones of the
adrenal cortex that produce cortisol. The drug is administered until a reasonable level of
cortisol production is achieved and the pet is then maintained on the drug at that level for
life, with periodic rechecks to adjust the dose.

"The treatment for iatrogenic Cushing's is slow withdrawal from the external source of
cortisol," continues Dr. Brinson. "It is extremely important that changes in the medication
are not made without first consulting your veterinarian. Quickly withdrawing the source of
cortisol before the adrenal glands can recover can lead to dramatic consequences, such as
vomiting, diarrhea, vascular collapse, and death."

The prognosis for this disease varies depending on the type. Surgery can cure an adrenal
cortical tumor that has not spread to other areas of the body. However, about half the
adrenal tumors are malignant and therefore may have already spread, in which case, there is
a much poorer prognosis. Pituitary-dependent Cushing's has a good short-term prognosis,
as the microtumors do not generally cause other problems. Long-term, however, pets with
Cushing's disease are predisposed to other diseases, such as diabetes mellitus, urinary tract
infections, kidney disease, hypertension, and pancreatitis. Iatrogenic Cushing's disease has a
good prognosis, if proper withdrawal times are maintained.

"It is important to remember two things about this disease," says Dr. Brinson. "First, two of
the most common signs of this disease are excessive drinking and urination. Excessive
drinking and urination are also the most common signs of other serious diseases, such as
kidney failure, diabetes, and hyperthyroidism (in cats), which need to be investigated prior
to testing the adrenal glands. Second, other conditions, such as arthritis and itchy skin, may
be masked by the excess cortisol production. These conditions are coincidental but may
surface as the Cushing's disease is treated and may require other forms of treatment."

If you would like further information about this condition, contact your local veterinarian.