Cushing’s Disease in Dogs – Top 3 Questions

Cushing’s disease in dogs can present in one of three ways:

  • Pituitary tumor (small gland at the base of the brain)

This is the most common cause of Cushing’s disease in middle-aged to older dogs.  Thankfully, it’s usually benign, meaning non-cancerous. There are rare cases of malignant tumors of the pituitary gland, but an otherwise healthy dog diagnosed with Cushing’s disease stemming from the pituitary gland has an excellent prognosis.

In a small percentage of dogs (approximately 15%), the tumor grows and presses on the brain. When that occurs, the dog may experience neurological symptoms. If this happens, the outlook for the dog’s prognosis is not as good.

The larger tumors that end up causing neurological symptoms are known as macroadenomas.  These are tumors that are larger than 1 cm. The smaller tumors, or microadenomas, are generally too small to cause neurological symptoms and can usually be managed with ongoing pharmaceutical treatment.
 

  • Adrenal tumor (two glands located near the kidneys)

Adrenal tumors come in second-place, but still only represent a very small percentage (around 15% to 20%) of Cushing’s disease in dogs. These tumors have roughly a 50/50 chance of being benign (non cancerous), or malignant (cancerous).

I’ve read several different articles and studies on the topic, and it seems there is a divide among professionals on whether to perform surgery or not.  Surgery is risky, and there’s no guarantee that another tumor won’t pop up in the pituitary gland.

The adrenal glands are what produce the “fight or flight” response when the dog is under stress.  It doesn’t have to be labelled as “good” stress or “bad” stress. The important thing is how much stress the dog has and how it is affecting his/her endocrine system.  Adrenal glands serve an important function in maintaining balance within the body by regulating digestion, the immune system, and energy.

The following YouTube video was created by a holistic veterinarian.


Digging deeper into the adrenal glands:

The adrenal glands might be small, but they are complicated and vital to the dog’s life. There are 3 zones within the adrenal gland:

  1. Zona Glomerulosa (Outer Layer)

This layer is responsible for secreting the mineralocorticoid hormones which transport sodium and potassium through the cell walls and maintain water balance, among other things.

2. Zona Fasciculata (Middle Layer)

This layer makes up 70% of the cortex and is responsible for secreting glococorticoid hormones (cortisol and corticosterone), the fight-or-flight stress hormones.

3. Zona Reticularis (Inner Layer)

This layer produces the sex hormones including progesterone, estrogen, and androgen., these hormones work together to sustain your dog’s life

  • Iatrogenic Cushing’s disease

The third type is caused by excessive use of corticosteroid medications (prednisone is one example) over time and is rare.

“Using the word “disease” to describe Cushing’s is not considered accurate by most veterinarian professionals. Once a dog has Cushing’s, he/she has the disease for the rest of his life. In that respect, Cushing’s is really considered a “syndrome”.”

  • Is it difficult to treat Cushing’s disease in dogs?

Trilostane: This particular drug is the only drug approved by the FDA to treat both pituitary and adrenal tumors. The medication works by stopping the over-production  of cortisol from the adrenal glands.  Side effects of Trilostane could include:

  • Poor appetite
  • Vomiting
  • Low Energy
  • Diarrhea

As of 2015, the FDA began adding additional side-effect possibilities to the packaging. Some of these side-effects might include severe sodium and potassium imbalance along with things like shaking and high liver enzymes.

Unfortunately, if your dog has other conditions that affect the kidneys, liver, or heart, is isn’t safe to administer Trilostane. Up until 1994, Trilostane was used for the human version of Cushing’s. Since then, it has been banned. It is still, however, considered a good choice for dogs by some veterinarians.

I’ve searched various opinions on whether this drug is found to be useful for dogs with Cushing’s, and the reviews are mixed.  Some veterinarians will not prescribe drugs like Trilostane until they are certain without a shadow of doubt that the dog has Cushing’s disease. 

Unfortunately, symptoms can be subtly, developing slowly over time. As our dogs age, it’s easy to shrug off minor things as a simple sign of aging. If no treatment plan is offered early on, the ongoing effects of too much cortisol in the body will deteriorate the dog’s health. If nothing is done until the signs are overt and obvious, it could be too late.

Treatment for Adrenal Induced Cushing’s Disease in Dogs

Possible surgery and medication:  If the veterinarian has diagnosed a tumor on your dog’s adrenal gland, the first line of treatment might be medication in order to shrink the tumor. Once the tumor is down to an operable size, surgery is sometimes the next step. Another option for veterinarians who would rather not perform surgery on the dog (surgery can be risky) is to treat with medications on an ongoing basis, possibly for the entire life of the dog.

Lysodren (or Mitotane)

Lysoden is a chemotherapy drug used in humans. Although not approved by the FDA, veterinarians can prescribe the medication as an “off label” product. That means it is still legal to prescribe if the veterinarian has reason to believe it’s a good option. However, the FDA has not conducted or approved studies on the actual effects of the drug on dogs.  Both Lysodren and Trilostane are potent drugs that can have a variety of side-effects, some more serious than others.

In fact, a review of the administration of Trilostane for dogs with Cushing’s (published by the Canadian Veterinary Journal in April, 2018, and written by Julie Lemetaylor and Shauna Blois), suggests a high degree of controversy around this drug. While the drug does inhibit the over-production of cortisol, it can also create a certain level of toxicity in the animal.

ScienceDirect has some interesting details about this particular drug and how it works on Cushing’s disease in dogs.

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About Lisa Theriault

Lisa Theriault wants you to know right up front that she is not a veterinarian. None of the articles/posts on this website are meant to take the place of veterinarian care. That said, Lisa has had a lifetime of experience dealing with dogs and plans on further education on dog anatomy and canine massage. In the meantime, Lisa's posts are all professionally researched and carefully crafted. The last thing she wants is to do or say anything that would hurt your dog. Stay tuned for more updates to Lisa's bio.