Cushings Disease
There are 3 forms of Cushings Disease. Most dogs have the more common form, Pituitary Dependent PD, with this form the dogs have a slow growing form of cancer that is located in the pituitary gland. This causes the adrenal glands to produce to much cortisol, because the tumor trigger to much ACTH to be produced.
The next form is the Non Pituitary, here there is a tumor in one or both of the adrenal glands. Here also to much cortisol is produced as a result of the tumor. The tumor is often malignant. The malignant tumor is called an Adenocarcinoma and it is aggressive where it can spread to other parts of the body and organs. The non cancerous tumor is called Adenoma.
The last form comes from Pets being on long dosages (long term use of) "Cortisone" , a drug used often on Pets. This drug comes in many forms. No matter what form it comes in it can cause problems with long term usage of this medication. This long term usage makes the body think it has more cortisone in the body that it does and then the body misreads the actual amount.
Signs of Cushings
Not all of these signs may be present, but as the disease progresses, they may become more pronounced or more signs may be seen. How common the sign is is shown for many of the items.
Diagnosis of Cushing’s can be complicated and difficult. It is important to determine the type of Cushings (adrenal, pituitary, or iatrogenic) so that the appropriate treatment can be undertaken.
Routine lab tests are usually performed – complete blood count, biochemistry, urinalysis – and abnormalities in these tests may suggest Cushing’s.
An abdominal x-ray may show an enlarged liver or adrenal gland changes.
An abdominal ultrasound is often performed to evaluate liver and adrenal glands.
A urine test measuring cortisol to creatinine ration is sometimes performed, but it is not a very specific test because many health problems can cause abnormal test results. This is a screening test only – a negative result rules out Cushing’s. A positive result does not confirm Cushing’s and more tests will need to be performed.
More definitive diagnostic testing looks at adrenal gland function. Cortisol levels in the blood are measured before and after a drug that would normally effect cortisol levels is given. Two commonly used tests are the ACTH stimulation test and the Low-dose dexamethasone suppression test. During the ACTH stimulation test, a pre-test blood sample is taken, then a dose of ACTH is given. After 2 hours, cortisol levels are measured again. If the cortisol levels are higher than expected, Cushing’s may be diagnosed. Dexamethasone is a cortisone-type drug that provides negative feedback on the pituitary gland to turn off ACTH production, and that in turn causes a decrease in adrenal cortisol production. In a normal animal (non-Cushing’s) a dip in cortisol would be seen 8 hours after giving dexamethasone. If a pituitary tumor exists, no drop in cortisol level is seen during the low-dose dexamethasone test. During a high-dose dexamethasone suppression test, cortisol levels will be suppressed in about 75% of dogs with PDH and will not be suppressed in the remaining 25% of dogs with PDH or in 100% of dogs with an adrenal tumor.