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Cushing's Disease in Dogs

Cushing's Disease, also known as hyperadrenocorticism, is a syndrome in which the adrenal glands are producing too much cortisol, or cortisone. Cushing's is more common in dogs than in cats. It is more common in middle-aged and older dogs. Generally, most dogs are diagnosed around nine to 10 years of age, however it can occur at any age. Slightly more female dogs are affected than male dogs. Large breed dogs tend to be affected more often than smaller breeds. Several breeds are more commonly diagnosed with Pituitary Dependent Hyperadrenocorticism, or PDH, than others, including poodles, terriers, German shepherds, dachshunds, beagles, and boxers. There are three types of Cushing's in dogs. They are:

  • Pituitary Dependent Hyperadrenocorticism, PDH - This is the most common type, occurring about 85% of the time. A tumor in the pituitary gland causes an increased production of ACTH (Adrenocorticotrophic hormone), which in turn signals the adrenal cortex to produce more cortisol. The tumor may be benign or malignant.

  • Adrenal Gland Tumor - This is the less common form of the disease. A tumor in one or both adrenal glands, which can cause an excess production of corticosteroids.  This tumor can also be benign or malignant.

  • Iatrogenic - This is medically induced Cushing's.

It is important to determine which type of Cushing's your dog has, so that appropriate treatment can be given.

Signs of Cushing's

There are various signs of Cushing's Disease. Not all of the signs may be present. And, often times, the signs are confused with other illnesses. However, as the disease advances the signs will usually become more pronounced. The most often observed signs of Cushing's are: 

  • Increased appetite - approximately 80-95% of dogs will show this sign. This can be confused with diabetes.

  • Increased drinking and urination - approximately 80-90% of dogs will show this sign. This is often confused with diabetes.

  • Elevated blood glucose - approximately 40-60% of dogs will show this sign.

  • Insulin resistance - up to 85% of dogs will show this sign.

  • Muscle weakness, lethargy, lack of activity - approximately 75-80% of dogs will show this sign. Excess cortisol causes protein breakdown, which leads to muscle weakness.

  • Bloated abdomen or "pot belly" appearance - approximately 90-95% of dogs will show this sign. This is due to an increase in of fat in the abdomen, an increase in liver size, chronically full bladder, stretching of the abdominal wall, and the abdominal wall becoming weaker.

  • Thin skin, flaky or greasy skin, bruising of the skin.

  • Skin infections.

  • Poor hair coat and thinning of the hair (usually on the sides), or difficulty with hair regrowth.

  • Excess panting - This is due to the increased fat in the rib area and muscle weakness.

Diagnosis

Diagnosis of Cushing's is complicated. And, often confused with other illnesses. If Cushing's is suspected, generally, routine lab test are done. Including, blood panels and urinalysis. A urinalysis will test for the ratio of cortisol to creatinine. However, these two tests should not be used as solely to diagnosis Cushing's. As many disorders can cause abnormal test results. A negative test result will rule of Cushing's. However, a positive test result does not confirm it either. More definitive testing must be done. An abdominal x-ray may show an enlarged liver and adrenal glands. Further, an abdominal ultrasound may be done to evaluate the liver and the adrenal glands. Further testing will still be done, the commonly used tests are the ACTH test, Adrenocorticotrophic hormone, and the low-dose dexamethasone suppression test.

With the ACTH test, a pre-test sample of blood is taken. Then, a dose of ACTH is given. After two hours, cortisol levels are measured again. If the cortisol levels are higher than expected, Cushing's may then be diagnosed

With the low-dose dexamethasone suppression test, a baseline cortisol level is measured. Then, a low dose of dexamethasone is given intravenously, and blood samples are checked again in eight hours. Sometimes a four hour sample is also drawn. This test is ideally performed in the morning.

Treatment

Once the type of Cushing's is accurately identified, appropriate treatment may begin. 

To treat PDH, surgery is very rarely performed. Radiation may be used to attempt to control the growth of the tumor. Medications are more frequently used. The most commonly used medicine is called Lysodren. This drug works by destroying the cortisol producing cells in the adrenal cortex. Careful monitoring is required during treatment. Treatment involves a loading phase, where, Lysodren is given daily, to rapidly bring symptoms under control. During the loading phase, owners must closely monitor their dog. Once he starts drinking normally, the maintenance phase begins. During the maintenance phase, Lysodren is then given two to three times per week. ACTH stimulation tests should be repeated every few months to ensure adequate control and dosing. Lysodren does have some serious side effects. Because of this some people decide to try other drugs to treat Cushing's. Another used drug is called Ketoconazole. This drug works by blocking the production of cortisol in the adrenal gland. This drug has the potential to create liver damage.

To treat the adrenal gland Cushing's medicine is generally give. Mainly, Lysodren and Ketoconazole. Surgery is difficult, therefore, rarely performed.

Iatrogenic Cushing's treatment requires that the medicine that is causing the Cushing's to be slowly discontinued. 

Related links about Cushing's in dogs:

http://www.lbah.com/canine/cushings.htm
Cushing's Disease Forum
http://www.io.com/~lolawson/cushings/
http://www.peteducation.com/article.cfm?articleid=416
http://www.agouravet.com/diseases/cushings.html

This site and its contents are intended to serve as basic informational purposes 
 --not a substitute for-- 
professional veterinary care!

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