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Cushing’s disease is a syndrome that occurs in pets
(and people) that is caused by an excess amount of cortisone (cortisol)
being present in the body. Mammals normally produce the hormone
cortisol in the adrenal glands. This hormone has a great number of
functions in the body but is primarily concerned with helping the
organism deal with stress. In the amounts normally produced in the
body, cortisol is a very useful and beneficial hormone. In fact,
neither you nor your pet can live without cortisol. The production of
cortisol is under control by the brain. The pituitary gland is the
primary controller of the cortisol levels in the blood. Under normal
circumstances, the pituitary gland monitors the amount of cortisol in
the blood. When the levels drop below a certain point, or when there is
some stress confronting your pet, the pituitary gland sends a hormonal
messenger; Adrenocorticotrophic (ACTH) hormone to the adrenal gland that
tells it to make and release more cortisol into the blood stream. As
the level of cortisol rises in the blood, the pituitary gland recognizes
it and then stops sending the ACTH, which allows the adrenal gland to
stop its release.
Cushing’s disease most commonly occurs when either
the pituitary gland does not “listen” to the presence of cortisol in the
blood, and continues to stimulate the adrenal glands (with ACTH)
regardless of the amount of cortisol in the blood. . The failure to
stop the ACTH release is caused by the presence of a small tumor in the
pituitary gland that does not obey the rules that normal pituitary cells
adhere to. These tumors are usually very small (about the size of a
pea) and rarely cause brain damage. Unfortunately, they continue to
stimulate the adrenal gland and so the body has to deal with the excess
cortisol. In rare cases (10-15%, the pituitary tumor can grow large
enough to put pressure on other parts of the brain. In these cases, the
pet may experience blindness, disorientation, circling, seizures and
other neurologic symptoms.
The second way in which Cushing’s
disease develops is if there is a tumor growing out of one of the
adrenal glands themselves. These tumors produce and release cortisol
without listening to the pituitary gland. Fortunately, this type of
tumor occurs in only 15% of the pets that develop Cushing’s syndrome.
Fifty percent of these tumors are benign adenomas which only cause the
problems associated with excess cortisol. The other 50% are malignant
tumors called adenocarcinomas. Unfortunately, these tumors may spread to
other parts of the body and eventually become fatal.
What are the symptoms of Cushing’s syndrome?
The symptoms of this disease are directly related to the effects of
cortisone on the body. They include:
| Excessive Thirst |
Panting |
Pendulous Belly |
| Excessive
urination |
Restlessness |
Weight Gain |
| Excessive
Appetitie |
Thin Hair and
Skin |
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Is this disease dangerous?
Excessive cortisol in the blood can lead to suppression of the immune
system, which can lead to excessive infections. It can also cause the
pet to develop Diabetes Mellitus, High Blood Pressure (Hypertension),
Strokes and Kidney Disease.
How do we diagnose this disease?
There are a number of tests used to diagnose Cushing’s disease. None of
the available tests can detect Cushing’s disease with 100% accuracy.
Generally, each test has about an 85% accuracy level. That means that if
one test is negative, but we still suspect that your pet has this
disease a second test might be warranted. We generally start with an
8-hour test called the Low Dose Dexamethasone Suppression Test. In this
test we take a sample of blood in the morning, then give your pet an
injection of a type of cortisone called dexamethasone. In normal pets,
this injection will cause the body to stop producing cortisone for about
8 hours. In pets that have Cushing’s syndrome, the level of cortisol in
the blood will rise by the end of the test.
An alternative test is the ACTH stimulation test. In this test, we take
a blood sample to measure the resting cortisone level. Then we inject
ACTH hormone. 1-2 hours later we take another sample. Normal dogs will
rise only so high in response to the ACTH while dogs with Cushing’s will
send their cortisol levels up beyond a certain level.
If either of these tests is abnormal, we then may have to do a second
test (High dose dexamethasone suppression) test to tell if the problem
is being caused by the Pituitary Gland or an Adrenal tumor.
How do we treat Cushing’s syndrome?
There are a number of options for treatment of this disease. We will
select the drug based on the severity of the problem, the size of the
pet and the costs of maintaining your pet on the drugs. The drugs
Lysodren, Trilostane and Ketoconozole are the three most frequently used
drugs for this problem. Each of them may cause side effects, some of
which can be serious. If your pet is diagnosed with Cushing’s disease,
we will inform you of the details surrounding each drug’s use.
How successful is the treatment:
For most of the pets that have pituitary dependant Cushing’s syndrome
(85% of the pets), the treatment is usually quite successful. These dogs
should be able to live pretty normal lives. They will need periodic
monitoring and slightly closer oversight than a non-cushingoid pet.
Those pets who have an Adrenal tumor do not have nearly the same
prognosis. These tumors do not readily respond to drug therapy and
surgical intervention is rather risky since the adrenal gland tumors
tend to grow into the vena cava.
If you have any questions about this topic or any aspect of your pet’s
health care, please feel free to ask our doctors.
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