Pituitary Dependent vs Adrenal-Based Hyperadrenocorticism in Dogs

Hyperadrenocorticism, also known as Canine Cushing's Disease, is an often overlooked condition in dogs.

Hyperadrenocorticism/Cushing's Disease

Canine Cushing's Disease (hyperadrenocorticism) happens in middle-aged or older dogs, and is therefore often considered to be normal changes as a result of old age.

Symptoms of Cushing's Disease

An enlarged abdomen and an increased appetite appear in 80% of dogs with Cushing's. Owners may think nothing of this other than their dog having a "healthy appetite." Obesity is a result of overeating.

Your dog may seem to be completely insatiable when it comes to food. Dogs suffering from Cushing's might have thinner skin and hair loss, or else a lackluster coat, and will consume more water and urinate more frequently.

The Difference Between Pituitary Dependent and Adrenal-Based Cushing's

Overall, regardless of whether your dog has Pituitary dependant hyperadrenocorticism (PDH) or Adrenal-based, the outcome is the same: the adrenal glands are over-producing steroids, and this can cause serious damage to your pet. But the two are different in their origins, and thus have different treatments.

Pituitary dependent hyperadrenocorticism: A properly functioning pituitary gland releases a hormone called ACTH. This hormone regulates the creation of cortisol (a type of steroid) in the adrenal glands. In a dog suffering from Cushing's, the pituitary is suffering from a tumor, which is causing it to create a heavy excess of ACTH. In turn, this tells the adrenal glands to create more cortisol. PDH accounts for approximately 80% of Cushing's cases.

Adrenal-based hyperadrenocorticism: This is much the same as PDH. The main difference being that in this case, the pituitary is likely functioning as it should and the tumor is located on the adrenal gland itself, causing it to overproduce cortisol. 

How A Vet Tells Them Apart

If a vet suspects your dog has Cushing's, she has a choice of what tests to perform. An ACTH stimulation test can be given to check for Cushing's, and takes about two hours. However this test doesn't tell your vet whether your dog suffers from Pituitary dependent hyperadrenocorticism or Adrenal-based hyperadrenocorticism, only if they have one of them. 

To determine that, a high dose Dexamethasone suppression test will be administered. Dexamethasone is injected, and is designed to suppress the secretion of ACTH in the pituitary. Blood needs to be taken before the Dexamethasone is given, at four hours after, and at eight hours after the injection to check cortisol levels. The results of this test can determine which form of Cushing's your pet is suffering from so that treatment can be determined accordingly. 

How Is It Treated?

A number of medications can be prescribed for both types of Cushing's. Adrenal tumors can often be surgically removed and the reoccurrence rate is low. The more worrisome prognosis is if the tumor on the adrenal gland is malignant and if it has already metastasized to other organs, thus rendering surgery a fairly useless option.

Surgery is not used for PDH. Pituitary tumors, when benign, are typically small and cause little damage aside from the oversecretion of ACTH. 

Drugs such as Lysodren, Anipryl, Ketaconazole, or Vetoryl can be used as oral treatments for hyperadrenocorticism. Each works in its own unique way with its own side-effects and risks and benefits, so do your research and speak to your vet about which option is best for your dog.