Cushing's Disease in Dogs
Cushing’s disease—also known as hypercortisolism and hyperadrenocorticism—is a serious disease that most affects middle-aged and senior dogs. It can be serious if left untreated.
Here’s what you need to know about Cushing’s disease in dogs—from types and symptoms to treatment and care.
What Is Cushing's Disease in Dogs?
Cushing’s disease (hyperadrenocorticism) occurs when the adrenal gland secretes too much stress hormone, or cortisol.
What Causes Cushing's Disease in Dogs?
Cushing’s disease in dogs is most commonly seen in middle-aged to older dogs—from about 7 to 12 years old.
There are three types of Cushing’s Disease in dogs:
Pituitary-Dependent Cushing’s Disease
Pituitary-dependent Cushing’s disease occurs when a tumor of the pituitary gland at the base of the brain secretes too much of the hormone that stimulates the adrenal gland to make cortisol.
These tumors are typically benign and small; however, 15-20% of patients with pituitary tumors will eventually develop neurologic signs as the tumor grows. Pituitary tumors are responsible for 80-85% of Cushing’s disease cases.
Adrenal Gland Tumor
The adrenal glands create stress hormones and are located right next to the kidneys. An adrenal gland tumor can be benign (not cancerous) or malignant (cancerous). Adrenal tumors cause 15-20% of Cushing’s disease cases.
Iatrogenic Cushing’s Disease
Iatrogenic Cushing’s disease in dogs is caused by excessive or long-term use of steroids.
What Does Cushing's Disease Do to Dogs?
While not inherently painful, Cushing’s disease in dogs (especially if uncontrolled) can be associated with:
High blood pressure
Chronic skin and urinary tract infections
Changes in the liver (vacuolar hepatopathy)
Increased risk of clots
High blood pressure and protein loss through the urine are fairly common with hyperadrenocorticism and can contribute to kidney disease.
Additionally, 15-20% of dogs with pituitary tumors develop neurologic signs as the tumor grows and 5-10% of Cushing’s patients will also develop diabetes.
Although rare, Cushing’s patients are also at risk for fatal blood clots called pulmonary thromboembolisms
Are Certain Breeds Predisposed to Cushing’s Disease?
Cushing’s disease is more commonly diagnosed in these breeds:
What Are the Symptoms of Cushing's Disease in Dogs?
There are a variety of symptoms that can appear in a dog with Cushing’s disease. Here are some of the most common signs of Cushing’s disease in dogs
Drinking more water
Hair loss or poor regrowth
Recurrent skin infections
Recurrent urinary infections
Seborrhea or oily skin
Firm, irregular plaques on skin (called calcinosis cutis)
How Is Cushing's Disease Diagnosed in Dogs?
Although there is no single test that will diagnose 100% of cases, your veterinarian will likely recommend some combination of the following:
Baseline bloodwork (CBC/Chemistry)
Urinalysis +/- urine culture (to rule out urinary tract infections)
ACTH stimulation test (can have false negatives)
Low-dose dexamethasone suppression test (can be affected by other illnesses)
High-dose dexamethasone suppression test
Urine cortisol to creatinine ratio
Abdominal ultrasound (can identify changes in liver and adrenal gland enlargement or tumors)
Computerized tomography scan or magnetic resonance imaging (can detect pituitary tumors)
What's the Treatment for Cushing's Disease in Dogs?
Treatment of Cushing’s disease in dogs is largely dependent on the underlying cause. Treatment options include:
If Cushing’s disease is caused by the excessive use of steroids, the steroid dosage should be carefully tapered down and discontinued. This may result in relapse of the primary disease the steroid was originally used to treat.
Pituitary and adrenal tumors can be surgically removed, and if benign, surgery can be curative.
If surgery is not an option, medical management with either trilostane
can be pursued. These drugs interfere with the production of cortisol, but very close monitoring is necessary to ensure that adrenal function is not impaired too much too quickly.
Depending on which medication is started, your veterinarian will create a plan for monitoring your dog’s bloodwork and reaching an appropriate dose (this will vary depending on patient, length of time on medication, etc.).
Once the vet has determined your dog’s proper dosage, an ACTH stimulation test should be done either every three to six months or if you notice signs of Cushing’s beginning to develop again. As pituitary and adrenal tumors progress, they will require an increased dose of medication to control symptoms.
While starting medication or changing dosages, please be sure to monitor your pet for lethargy, vomiting, decreased appetite, or trouble breathing, and call your veterinarian immediately if any of these signs are noted.
Radiation treatment for pituitary-dependent Cushing's disease in dogs has been shown to improve or eliminate neurological symptoms and improve the prognosis, especially when treated early. The median survival time in these cases is 743 days.
How Long Do Dogs with Cushing's Disease Live?
The prognosis for dogs with Cushing’s disease is dependent upon pituitary vs. non-pituitary-dependent Cushing's and whether the tumor is benign or malignant.
If caused by a small pituitary tumor, medical management can provide long-term control with good quality of life. For pituitary-dependent Cushing’s disease, the median survival time of patients treated with trilostane or mitotane is about two to two and a half years.
If a pituitary tumor is large and affects the brain and surrounding structures, the prognosis is poorer.
Approximately 50% of adrenal tumors are benign, and surgical removal is curative. The other 50% of adrenal tumors are malignant and carry a poor prognosis, especially if they have already metastasized at the time of diagnosis.
The median survival time is approximately one year when treated with trilostane. The prognosis is worse in patients with metastasis of the primary tumor, local invasion of the vessels, or a tumor greater than 5 cm in length.
Can You Prevent Cushing's Disease in Dogs?
Unfortunately, you cannot prevent Cushing’s disease if it is caused by a pituitary or adrenal gland tumor.
However, you can avoid long-term use of steroids to minimize the risk of developing iatrogenic Cushing’s disease.
Featured Image: iStock.om/MmeEmil