Cushing’s Disease in Dogs
Cushing’s Disease (Hyperadrenocorticism) is an overproduction of cortisol in the blood, caused by a tumor of either the pituitary or the adrenal gland. In the normal dog, the pituitary gland (responsible for hormone production in the body) produces a hormone called ACTH, which stimulates the adrenal gland to produce the glucocorticoid hormones necessary for the function of many systems in the body, including the metabolism of proteins and carbohydrates. If something goes wrong in the pituitary gland or adrenal gland and too much glucocorticoid is produced, then Cushing’s disease develops.
80-85% of Cushing’s cases result from a pituitary tumor . . . almost always benign. 15-20% result from an adrenal tumor, and half of those are malignant and will spread.
It seems that Cushing’s is being diagnosed in dogs at increasing rates, which for me begs the question, why?
What causes these tumors of the pituitary and adrenal glands?
There is also a “temporary” form of the disease caused by long-term or an overuse of steroids. In this form, “iatrogenic” Cushing’s disease, the symptoms go away once the steroids are discontinued. A question that comes to mind for me is, what correlation is there between dogs that have had high steroid use at a younger age, and those that develop Cushing’s later in life . . . maybe none but it would be an interesting study.
But for those cases that are permanent, what can we do to reduce the chances of disease in healthy dogs?
It typically is seen in middle-aged and older dogs, is evenly distributed between males and females, and is not pre-dispositioned to any particular breed. One theory as to the recent increase in cases is that the disease progresses slowly symptoms come on gradually so the condition is often times undiagnosed, written off to just aging. The symptoms include unexplained hair loss, increased water consumption, and a “pot-belly” appearance, from the shifting of fat to the abdominal area. Also, some dogs will have only one symptom while others may have many.
For dogs ultimately diagnosed with Cushing’s disease, hair loss was one of the most common reasons the owners first brought their dog in for evaluation.
Interestingly one of my Shelties, Ziggy, was diagnosed at age 9 ½. His only symptom was unexplained and extreme hair loss and after doing every autoimmune test, skin test, etc., we decided to test for Cushing’s. The results were pretty convincing. Within three months of medication, his coat had returned. Within 9 months his coat grew thick and silky and strong . . . a coat he had never before had. He also returned to puppy like energy and enthusiasm.
Cushing’s Disease is difficult to diagnose and there is no single conclusive test. Appearance of symptoms along with lab tests for blood (increased white blood cell count, increased liver enzyme ALP, increased blood sugar, cholesterol, and dilute urine) provide evidence that a dog may be Cushinoid, which leads to additional testing, specific to Cushing’s. These tests: Urine cortisol/creatinine ratio, ACTH and Dexamethosone suppression help to determine the source of the disease; pituitary or adrenal dependent. In some cases the results are clear and in other cases, as series of tests need to be performed.
Treatment of Cushing’s can include tumor removal in some adrenal tumors. For pituitary tumors that are 80% benign, treatment is an oral medication of Vetoryl or Lysodren and dogs can lead a normal and long quality life but do need to be tested annually to make certain the dosing is correct.
I still go back to the question of why we are seeing an increase in Cushing’s diagnoses . . . perhaps we are more in tune with our dogs, they are members of the family and we are more conscientious of their health, or perhaps there are external toxins they are exposed to that lead to tumors. Just as with people, their environment and what we put in their bodies is increasingly important to consider.