|
Cushing's Disease occurs most commonly in the dog,
but is sometimes seen in the cat and ferret as well.
The disease is characterized by an excess of a hormone
known as cortisol which is produced by the adrenal glands.
These paired glands in the dog and cat, are located
just above each kidney. The cortisol hormone produced
by the adrenal glands is more commonly referred to as
adrenaline. This hormone assists all mammals in
times of stress, and is sometimes called the "fight
or flight" hormone. When in excess, cortisol
can cause serious problems.
The cortisol produced by the adrenal glands, is under
control by another gland located in the base of the
brain, called the pituitary gland. This gland
is also known as the "master" gland of the
body, controlling the production of many hormones such
as thyroxin or thyroid hormone as well. Tumors
in either the pituitary gland, or the adrenal gland,
will ultimately cause the syndrome known as Cushing's
disease.
When a tumor develops in the pituitary gland, the resultant
condition of Cushing's disease is referred to as secondary
Cushing's syndrome or pituitary dependant hyperadrenocorticism
(PDH). This is the most common form of the disease,
occurring in approximately 80% of the patients diagnosed
with Cushing's disease.
If the tumor is located in the adrenal gland(s) it
is simply called primary Cushing's syndrome. Blood
tests can diagnose the presence of this syndrome, and
can also determine in the majority of cases, which of
the two syndromes exist.
This becomes important when considering the treatment
options available for Cushing's disease.
With secondary Cushing's syndrome or PDH, the tumor
in the pituitary gland is most often considered a benign
tumor, which simply is over-secreting the hormone controlling
the production of cortisol, known as ACTH. This
over-production of ACTH hormone, then results in an
over-production of cortisol from the adrenal glands.
Primary tumors in the adrenal gland(s) are typically
malignant tumors or cancerous tumors, and produce an
excess of cortisol hormone without the influence from
the pituitary gland's ACTH.
Symptoms of a dog affected with either primary or secondary
Cushing's syndrome commonly include: excess thirst and
excessive urination, pot bellied appearance to the abdomen,
weakness or laziness, thinning of the hair coat with
poor regrowth of hair; some cases have an increased
appetite, and develop plaque like lesions on the skin.
If your dog is experiencing any 3 of the above symptoms,
blood testing for Cushing's disease is in order.
When the diagnosis of Cushing's disease is confirmed,
treatment options are as follows. With secondary
Cushing's or PDH, treatment is most often accomplished
by medication taken orally. To date there are
three drugs available for the treatment of PDH including
Lysodren, Anipryl, and Ketoconazole.
Of these drugs, Lysodren is by far the most commonly
used, but can be associated with side effects of nausea
characterized by vomiting, diarrhea, and/or decreased
appetite. If any of these symptoms occur while
on this medication, discontinue the drug, and check
with your veterinarian. Otherwise, this medication
is given daily for a course of approximately 2 weeks;
the patient's blood is then retested to determine if
control of the excessive production of cortisol has
been accomplished.
If so, the maintenance dose of Lysodren is then continued
twice weekly. If Lysodren fails to work, either
the dose was inappropriate, or the patient has primary
Cushing's syndrome which does not respond to oral medication
of any kind. Increasing the dose of Lysodren,
or switching to another drug is often recommended when
there is an initial failure to respond to treatment.
In cases of primary Cushing's disease, the adrenal
tumor(s) responsible for the over-production of cortisol
must be removed. This surgery however, is made
difficult in most cases of primary Cushing's, because
of the location of the adrenal glands near vital tissues,
and the aggressive behavior of the tumors themselves.
If tumor removal can be successfully accomplished, the
condition is considered cured. Most cases of adrenal
tumors however, cannot be successfully removed.
|
