Also known as hyperadrenocorticism, canine Cushing’s disease takes place when the adrenal glands start producing too much cortisol. In order to better understand Cushing’s disease and its effects on dogs, it’s necessary to better understand the basics involved in the normal functioning of the dog’s endocrine system with a focused insight on the pituitary and adrenal glands. When these glands are functioning properly, as in a normal, healthy dog, there are typically no signs of trouble or suggestions of disease; instead, problems start when these glands start overproducing too much of the hormone cortisol. As with many things in life, too much of a good thing turns out being not so good.
The Normal Functioning of the Dog’s Pituitary and Adrenal Glands
The pituitary gland is a pea-sized endocrine gland located at the base of the dog’s brain. This gland is responsible for triggering the production of a hormone known as the adenocorticotrophic hormone, often abbreviated as ACTH. When this hormone is released into the dog’s bloodstream, it stimulates the dog’s two adrenal glands to further secrete another important hormone known as cortisol.
Cortisol is a naturally-produced steroid responsible for helping the body respond to stressful situations. This hormone engages in many important, life-sustaining functions such as the regulation of blood sugar levels, the metabolism of fat and a variety of other functions involving the dog’s kidneys, cardiovascular system, skeletal system, nervous system and immune system.
When the pituitary and adrenal glands are functioning well, the levels of ACTH and cortisone fluctuate based on needs; however, when cortisol levels get high, the pituitary gland stops secreting ACTH, and when cortisol levels get low, the pituitary gland works harder so to secrete more ACTH. This whole unbalanced performance is what leads to a cascading chain of events.
Forms of Cushing’s Disease
Things start getting problematic when dogs develop tumors on the pituitary or adrenal glands or when certain medications interfere with their proper functioning. When this happens, too much cortisol circulates in the body with the end result of weakening the dog’s immune system and leaving his body vulnerable to infection and diseases. There are three forms of Cushing’s disease in dogs: pituitary-dependent, adrenal-based and Iatrogenic. All three of them, cause the body to be inundated with excessive, troublesome cortisol.
The great majority of dogs are affected by this form of Cushing’s disease. In dogs with pituitary-dependent Cushing’s disease, their pituitary gland develops a small, benign tumor which causes the over secretion of ACTH. Despite the large amounts of ACTH, the adrenal glands continue secreting cortisol. At the same time, the pituitary glands, fail to recognize the elevated levels of cortisol and continue releasing more ACTH which leads to a cascading chain of events. Typically, dogs affected by this form of Cushing’s disease develop enlarged adrenal glands because these glands are constantly working.
At times, a tumor on the adrenal gland is responsible for causing excessive secretion of cortisol. The tumor in this case can be benign, but there are also chances it may be malignant and prone to metastasizing to the lungs and liver. As in the case of pituitary-dependent Cushing’s disease, the balancing act between the pituitary gland and the adrenal glands is disrupted causing the overproduction of cortisol to flood the bloodstream.
This third type of Cushing’s stems from a totally different dynamic compared to the previous ones. In this case, the condition is medically induced when a dog is given too many corticosteroids to treat conditions such as allergies. Often this condition can be easily prevented by carefully tapering off the cortisone medication gradually over the course of several days. Thankfully, this form of Cushing’s disease is transitory and reversible.
Because cortisol plays many roles, its excessive production triggers a vast array of symptoms that often may appear vague and can be easily confused with signs of normal aging in senior dogs. Cushing’s disease can be defined as a great imitator because its clinical symptoms are very similar to those of several other health conditions. Following are some common symptoms of Cushing’s disease in dogs.
- Increased drinking
- Increased urination
- Inappropriate urination
- Increased appetite
- Loss of muscle mass
- Pot-bellied appearance
- Excessive panting
- Thinning of hair
- Dull coat
- Bruises on skin that heal slowly
- Recurrent skin infections
Clinical signs alone often aren’t sufficient from a diagnostic perspective; indeed, in most instances, further testing is needed. Blood work and urine testing may reveal some hints of the presence of a disorder requiring more definite tests. The best tests to help pinpoint Cushing’s disease consist of a urine cortisol and creatinine ratio test, an ACTH suppression test and a high dose dexamethasone test. An ultrasound often turns out helpful in detecting the presence of a tumor on the adrenal glands. Yet, even with these test results, Cushing’s disease remains a condition that is overall quite challenging to diagnose.
The treatment for Cushing’s disease varies depending on the cause. In the case of adrenal tumors, surgery through an experienced surgeon may be indicated. When surgery is not indicated, medications will need to be prescribed. Treatment for the pituitary-induced Cushing’s disease requires long term administration of drugs. The most common drugs used are mitotane (Lysodren) and trilostane (Vetoryl). On the other hand, when it comes to the iatrogenic form of this condition, treatment focuses on carefully discontinuing the steroid that is being administered. It’s important that the weaning-off process is conducted in a controlled, systematic manner under the vet’s guidance so to avoid complications.
The Bottom Line
The only real definite cure for Cushing’s disease consists of the removal of the adrenal gland tumor when caught at an early stage and when the tumor hasn’t had a chance to spread, explains Anna Stohlman, a veterinarian working for the FDA’s Center for Veterinary Medicine. However, because the surgical procedure is quite complex and there are several risks involved, many choose to manage it through the use of medications. Fortunately, through careful monitoring, dogs with Cushing’s disease can lead a good quality of life as long at their owners are diligent in administering medications and are willing to follow up on routine blood work.
- U.S. Food and Drug Administration: Treating Cushing’s Disease in Dogs
- Washington State University: Cushing’s Disease
- Seattle Veterinary Services: Cushing’s Disease
- American College of Veterinary Internal Medicine: Cushing’s Syndrome