Cushings Disease in DogsCushings Disease in dogs is a medical condition caused by an overproduction of steroid hormones. There is no known "cause" of Cushings Disease, but it is always due to a tumor - either in the adrenal gland (in the belly,near the kidneys) or in the pituitary gland (in the brain). It's not known why these tumors occur, but they canhappen in any breed of dog, usually in the middle to senior age range.
Most dogs with Cushings Disease will show similar signs. The first and most noticeable signs to owners are the increase in drinking, and the increase in peeing. These signs are NOT, however, only signs of this disease. MANY medical conditions make dogs drink and pee more. (See the Symptoms section in the Dog Health Problems page.) This increase can be quite dramatic, to where it seems that all that the dog ever does is drink bowls full of water and then pee it all out. They can have problems with incontinence too, simply because of the large volume of urine they are producing. Many cushingoid dogs will pant more than normal. Once again, just because your dog is panting does not mean that he has Cushings Disease! This is another very non-specific sign. Other causes of panting can be found in the rapid breathing topic on the Emergencies page. Most dogs with advanced or chronic Cushings Disease will develop what appears to be a swollen belly, called a distended abdomen in vet parlance. They do not actually have a larger abdomen though, but a weakening of the abdominal muscles. This causes the belly to change shape and appear different, more pendulous or droopy to most peoples eyes. And again, a swollen belly is not ONLY caused by Cushings disease, and may in fact be an emergency. And, also with advanced disease, there will be bilterally symmetrical hair loss. Bilaterally symmetrical means equal on both sides of the body, both in location and in amount. This can be seen with other diseases of the endocrine system too, like with hypothyroidism in dogs.
The diagnosing of Cushings Disease in dogs is reasonably straight forward. A specific test is run, called an ACTH Stimulation Test. For this test, the dogs blood is drawn and held. Then the dog is given an injection of the hormone ACTH. After 1-2 hours, another blood sample is drawn. Then the blood is sent to a laboratory and the cortisol (steroid) levels in both samples are measured. The dogs values are compared to normal levels, and the veterinarian determines if Cushings Disease is present. This test is the best way to diagnose Cushings Disease in dogs, but it is on the expensive side (plan for around $200). The hard part is determining if the disease is from a pituitary or an adrenal tumor. Many tests are available to help with this, but no one single test is definitive. Blood tests called dexamethasone suppression tests can be done - they are inexpensive, but can be difficult to interpret or can be inaccurate. An abdominal ultrasound can be done to look for enlarged adrenal glands. Visible enlargement of one or both adrenal glands still doesn't absolutely confirm Cushings Disease from an adrenal tumor. Biopsies can be done of the affected gland(s) - if these are negative for tumor, then the issue is in the pituitary gland, in the brain. It could easily cost a thousand dollars to do all of this. Alternatively, a CT scan or MRI of the brain can be done looking for a pituitary tumor. This can be quite expensive, in the thousands of dollars in some areas. If there is no pituitary tumor, it can be inferred that there is an adrenal tumor..... Not exactly an easy diagnosis here.
Why do we need to know where the tumor is, if it is benign? Well, if we can show for sure that the tumor is in one adrenal gland, then a surgery to remove that gland is curative - the dog no longer has Cushings Disease. This is really the best case scenario for the dog, although it is very hard on the owners pocketbook, and the surgery is not a simple one. Nothing about Cushings Disease in dogs is simple, or cheap.... Most of the time, the disease is caused by a pituitary tumor. Luckily, there are medications to treat Cushings Disease regardless of where the tumor is. These are also not inexpensive, unfortunately, but are less expensive than some of the other options we've discussed. Two medications are often used. They are mitotane and trilostane. Again, using either of these medications is not simple, or cheap. It is easy to over-do the treatment, in which case you end up with a whole other problem, Addisons Disease. And the medications are hard on the dogs system too - they should have normal liver and kidney function to be on either medication. To use either mitotane or trilostane, the individual dog's dose is titrated to effect. This means that the inital drug dose is calculated with a formula, treatment is begun, and repeated ACTH Stimulation Tests are run over time, adjusting the dose each time to try to fine tune to the best dose for that dog.
The information presented here is not meant to replace the advice of your own veterinarian! A valid veterinary-client-patient relationship (created when you take your pet to see your vet) is essential to providing excellent individual pet care. If your pet is ill, call or go to your vet or an emergency veterinary hospital!
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As mentioned above, Cushings Disease in dogs is always caused by a tumor. The tumor itself is benign, meaning that it isn't a big bad "cancer" that will spread throughout the body. If the tumor is in the pituitary gland, then it causes that gland to make more of a hormone, normal in the body, that tells the adrenal glands to make more steroid hormone. If the tumor is in the adrenal gland, then the tumor itself makes too much steroid hormone. Either way the effect on the dog is the same.
