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.
Latrogenic 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.
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