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What is Cushing's disease?
Simply put, Cushing's disease is an excess of cortisol in the blood
stream. There are three main causes of Cushing's disease:
1) Approximately 85-90% of naturally occurring Cushing's cases are due to a microscopic tumor of the pituitary gland, a small gland just under the brain. Thankfully, most of these tumors are benign.
The tumor sends signals (ACTH) to the adrenal glands which cause them to enlarge and produce too much cortisol.
2) The other 10-15% of naturally occurring Cushing's cases are caused
by a tumor on one or both adrenal glands. Unfortunately, about half of these tumors are malignant (cancerous). The
tumors produce too much cortisol on their own without any input from the pituitary.
3) Cushing's disease can also be caused by medications. Many steroid medications
(prednisone, dexamethasone, triamcinolone, etc.) can cause Cushing's disease because they act just like cortisol. This form of Cushing's disease can be reversed by changing medications or decreasing the dose of the medication being used. CAUTION!: Sometimes steroid medications are used to prevent a life threatening disease and Cushing's disease is an unavoidable side effect. Never change or alter your pet’s steroid medications without consulting your veterinarian!
What are symptoms of Cushing's disease?
Below are the most common symptoms of Cushing's disease. There are many more and not all symptoms
occur in every case. These symptoms can be very subtle.
Appetite increase
Increased water consumption
Increased urine volume
Frequent bladder infections
Black heads on skin (comedones)
Blindness
Decreased interest in exercise
Enlarging abdomen
Hair loss involving back and tail
Long term or recurring skin infections
Panting
Thinning skin
Weight gain
What are the consequences of Cushing's disease?
Elevated levels
of cortisol put extra strain on all organs especially the pancreas,
heart, liver and kidneys. The liver swells from the effect of the
cortisol. Uncontrolled Cushing's disease can also lead to diabetes
or blood clots in the lungs. High levels of cortisol affect the
immune system, causing frequent infections of the bladder and skin.
Pets may be restless, anxious, and be unable to hold their urine,
leading to house soiling problems. Cushing's disease also causes
thinning of the hair coat and even baldness.
How do we test for Cushing's disease?
Routine blood and
urine tests do not diagnose Cushing's, but can indicate changes of
organ function from the disease. Specific tests can be run that
will show how the adrenal glands are functioning:
ACTH stimulation test:
For this test a blood sample is drawn to determine the baseline level of cortisol in the blood stream. Next an injection is given of synthetic ACTH which mimics the hormone normally released by the pituitary. After a period of time, another blood sample is drawn to evaluate the new blood level of
cortisol. This test will also be used to monitor the effectiveness of
treatment.
Low Dose Dexamethasone Suppression Test:
To perform this test a blood sample is drawn to evaluate the baseline level of cortisol in the blood stream. Next an injection of a steroid is given.
Blood samples are drawn 4hrs and 8hrs later.
Normal pets
respond by reducing the cortisol level after the injection,
Cushing’s pets do not. This test can also help your veterinarian
decide if the problem lies at the level of the pituitary or at the
level of the adrenal glands.
Imaging - radiographs (x-rays) and ultrasound:
These tests are needed if there is a suspicion that the cause of Cushing's is due to an adrenal gland problem. Because
half of adrenal tumors are cancerous, your pet’s doctor may want to try to visualize the adrenal glands to determine if a more aggressive approach is needed.
How is Cushing's treated?
There are many ways to treat Cushing's but we will cover the most popular three:
Mitotane (o,p’-DDD) (Lysodren®)
Mitotane
is used to carefully and specifically destroy some of the cells of
the adrenal gland that produce cortisol. Careful monitoring of the
effects of this drug is necessary, using the ACTH stimulation test.
Too much of the drug can permanently destroy the adrenal gland,
causing an underactive (hypoadrenocorticism) condition that can be
life threatening.
Side effects to watch for: Lethargy, ataxia (drunken appearance),
weakness, vomiting/diarrhea.
l-deprenyl (Anipryl®) (Selegiline)
Selegiline is occasionally used in treatment of Cushing disease that originates from the pituitary gland. Selegiline will mimic a hormone that blocks the release of ACTH. Less ACTH results in less cortisol and fewer Cushing's signs.
Side effects to watch for: Vomiting, diarrhea, restlessness, lethargy, salivation, and not eating.
Trilostane®
Trilostane® directly prevents the production of cortisol which results in lowering the body’s cortisol
levels (the main goal of Cushing therapy!)
In the past,
Trilostane had to be imported from Europe, but is now available in
the USA.
Side effects to watch for: Lethargy, decreased appetite, vomiting, diarrhea.
What are the long term expectations?
Successful treatment reduces the symptoms associated with the
disease. Pets feel better, drink less water, and their skin and
hair coats improve dramatically.
Every 6 – 12 months an ACTH
stimulation test needs to be run to assure the proper dose of the
medication is being used. Cushing’s is a progressive disease (that
means it will change over time). While being maintained on the
proper dose of therapy your pet’s quality of life is usually good to
excellent. Many pets live a normal life with treatment.
For more information on Cushing's disease visit www.veterinarypartner.com
Written by Daniel J. Gray, DVM
References:
Plumb, Donald. Veterinary Drug Handbook 4th ed. PharmaVet Publishing. White Bear Lake, 2002.
Tilley, Larry P. and Smith, Francis W.K. Jr. The 5-minute Veterinary Consult: Canine and Feline 2nd ed.
Lippincott Williams & Wilkins. Baltimore, 2000
Veterinary Information Network. www.vin.com
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