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Library
of Pet Health Topics at Brown County Veterinary
Hospital...
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| Cushing Disease
(Hyperadrenocorticism) |
| What is Cushing disease? |
What is Cushing disease?
Simply put, Cushing disease is an excess of cortisol in the blood stream. Extra cortisol causes different symptoms and consequences that we will discuss later. There are three main causes of Cushing disease:
#1 Approximately 85-90% of naturally occurring Cushing cases are due to a microscopic tumor of the pituitary gland. (Pituitary gland is a small gland just under the brain) Thankfully, most of these tumors are benign. A pituitary tumor sends excess signals (ACTH) to the adrenal glands (adrenal glands are right in front of both kidneys) which cause the adrenal glands to enlarge and produce too much cortisol.
#2 The other 10-15% of naturally occurring Cushing cases is due to a tumor on one or both adrenal glands. Unfortunately, about ½ of these tumors are malignant (cancerous). The tumorous adrenal glands produce too much cortisol on their own without any input from the pituitary.
#3 Cushing disease can also occur due to medications. Many steroid medications (prednisone, dexamethasone, triamcinolone etc.) can cause Cushing disease because they act just like cortisol. Too much steroid medication can create the Cushing disease. This form of Cushing 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 diseases and Cushing disease is an unavoidable side effect. Never change or alter your pet’s steroid medications without consulting your veterinarian!
What are symptoms of Cushing disease?
Below are the most common symptoms of Cushing disease. There are many more and not all symptoms are needed to begin testing. In pets with Cushing disease the symptoms can be very subtle.
-Appetite increase
- Black heads on skin (comedones)
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Blindness
- Decreased interest in exercise
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Drinking increased
- Enlarging abdomen
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Hair loss involving back and tail
- Increased anxiety
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Long term or recurring skin infections
- Panting increased
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Thinning skin
- Weight gain that is difficult to control
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Urination frequency increased
What are the consequences of Cushing disease?
Consequences of Cushing disease are three fold:
#1 Elevated levels of cortisol put extra strain on all organs especially the pancreas, heart, liver and kidneys. Your pet is literally under stress constantly with no way to relax! In worst case scenarios this excess strain can lead to diabetes or blood clots in the lungs.
#2 The second consequence of Cushing disease is having an unlivable companion. Increased anxiety and increased drinking can cause pacing, panting and urinating in the house. This can make some pets difficult or impossible to live with.
#3 The final consequence is cosmetic. In middle to late stages of the disease the hair can thin and the skin change color. Some pet owners find this very distressing.
How do we test for Cushing disease?
If you are considering testing then you or your veterinarian have a suspicion that your pet may have Cushing disease. This suspicion may have come from the symptoms above and possibly from liver associated signals on a blood panel or even a special type of urine test that was run by your pet’s doctor. When the decision is made to test for Cushing disease one of several tests may be run.
#1 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 second level will be affected by the ACTH given previously. Based on how the cortisol levels change in response to the ACTH injection is how your veterinarian will begin to diagnose whether or not your pet has Cushing disease. This test will also be used to monitor the treatment of Cushing disease if treatment is deemed necessary.
#2 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. Another blood sample is drawn 4hrs and 8hrs after the steroid injection is given. Based on how your pet’s cortisol levels react to the steroid at 4 and 8 hours, your veterinarian will begin to determine whether or not your pet has Cushing disease. 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.
#3 Imaging (radiographs[X-rays] and ultrasound):
These tests are needed if there is a suspicion that the cause of Cushings is due to an adrenal gland problem only (pituitary not involved). Because ½ of cases that involve the adrenal gland only 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 treated?
There are many ways to treat Cushing but we will cover the most popular three:
#1 Mitotane (o,p’-DDD) (Lysodren®)
Mitotane is used to carefully and specifically destroy some of the cells of the adrenal gland and also partially block the function of the adrenal gland. Careful monitoring of the effects of this drug is needed to ensure that too high of a dose is not used. On average 1-2 ACTH stimulation tests will need to be performed to monitor therapy. If your pet is sensitive to the medication more than 2 ACTH stimulation tests will be needed.
Side effects to watch for: Lethargy, ataxia (drunken appearance), weakness, vomiting/diarrhea
#2 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 signs.
Side effects to watch for: Treatment failure is the number one side effect!
Other effects include: vomiting, diarrhea, restlessness, lethargy, salivation, and not eating
#3 Trilostane®
Trilostane® directly prevents the production of cortisol which results in lowering the body’s cortisol levels (the main goal of Cushing therapy!) However,
the main problem with Trilostane® is that it has to be imported from overseas which requires weeks of FDA paper work and patience!
Side effects: Lethargy, decreased appetite, vomiting, diarrhea
What are the long term expectations?
After a treatment is chosen (usually mitotane therapy) and the initial phase of treatment is complete, the treatment will be twice daily for the life of your pet. Every 6 – 12 months an ACTH stimulation test needs to be run to assure the proper dose of the medication is being used. Cushing is a progressive disease (that means it will change over time) therefore more medication is usually needed in the future. While being maintained on the proper dose of therapy your pet’s quality of life usually fair to excellent. According to the text book, the life expectancy of a pet after diagnosis of Cushing disease is 2-4 years. It is of the author’s opinion that the life expectancy can be longer than 4 yrs.
For more information on Cushing 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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