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Cushing’s Disease is an endocrine disorder affecting the adrenal glands. In humans and dogs, the endocrine system is like a messenger system that involves chemicals being released into the bloodstream, and these chemicals travel to distant target organs to act on them. The adrenal glands are responsible for producing numerous substances that can affect levels of sugar and salt in the body, and they can produce sex hormones like testosterone and estrogen.
With Cushing’s Disease, excess amounts of cortisol are released into the bloodstream by the adrenal glands. This condition is also known as hyperadrenocorticism, and it is one of the most common endocrine issues in dogs. It primarily affects middle-aged to older dogs, and certain dog breeds like Poodles, Dachshunds, Boxers, Boston Terriers, and Yorkshire Terriers have a higher risk for developing Cushing’s Disease1.
Almost 85% of these cases are caused by a benign tumor on the pituitary gland. The pituitary gland is a very small organ located within the base of the brain that controls several other hormone-releasing glands. When a pituitary tumor is present, this is referred to as pituitary-dependent hyperadrenocorticism or PDH. The tumor causes the pituitary gland to continuously send a signal to the adrenal glands to keep releasing cortisol into the bloodstream. For small breed dogs with Cushing’s Disease, they are more likely to have this type of hyperadrenocorticism.
The other 10-15% of Cushing’s Disease cases are caused by a tumor that forms on the adrenal gland itself. Like with PDH, the adrenal gland is continuously stimulated to release cortisol into the bloodstream. The tumor can be benign (adenoma) or malignant (adenocarcinoma). Large breed dogs with Cushing’s Disease are more likely to have this type of hyperadrenocorticism.
Some cases of Cushing’s Disease can be caused by excessive use of oral steroid medications like prednisone or triamcinolone. This is known as iatrogenic Cushing’s. Routine examinations and lab work are critical for patients using steroids long term.
Clinical signs of Cushing’s Disease in dogs can be subtle like lack of energy. Skin issues like hair loss and darkening of the skin can be confused for allergies or other endocrine issues like hypothyroidism. However, the presence of hard white scaly patches on the elbows and knees, known as calcinosis cutis, is rarely caused by other conditions.
Some of the most common clinical signs include increased thirst, increased urination, and increased appetite. Excess cortisol levels can cause muscle wasting and, when combined with weight gain, can result in a pot-bellied abdomen. Increased panting, infertility, and poor healing of wounds are also symptoms of Cushing’s Disease in dogs.
Cushing’s Disease can be difficult to diagnose without a thorough medical history and baseline diagnostic testing. You may notice that your dog has one or some of the clinical signs mentioned above. Cushing’s Disease can sometimes cause elevated liver enzymes, increased glucose, and high cholesterol on blood work. Urine samples from Cushing’s patients can show signs of a urinary tract infection and contain excessive levels of protein. A screening tool called the urine cortisol creatinine ratio test, or UCCR test, can be utilized. When it is normal, your dog does not have Cushing’s Disease. However, an abnormal result warrants additional testing.
A special blood test is known as a low-dose dexamethasone suppression test, or LDDS test is considered the gold standard for diagnosing Cushing’s disease. The test is performed over an eight-hour period. A baseline blood sample is collected, and then a low dose of a steroid called dexamethasone is administered to your dog. The man-made cortisol (dexamethasone) should suppress the adrenal glands from releasing more cortisol. Blood samples are collected again at the four-hour and eight-hour marks. If the eight-hour number is elevated, then your dog is likely to have Cushing’s disease. An elevated eight-hour number in the face of a normal four-hour number is suggestive of PDH, whereas a dog might have an adrenal gland tumor if both numbers are elevated.
An alternative test, known as the ACTH stimulation test, may provide more accurate results than the LDDS test in certain circumstances. ACTH stands for adrenocorticotropic hormone and is released from the pituitary gland. ACTH should cause the release of cortisol when it is administered. A baseline blood sample is collected, and then another sample is collected one hour after ACTH has been administered. If the numbers are high, then your dog might have Cushing’s disease. However, this test does not distinguish PDH from an adrenal tumor. The ACTH stimulation test is recommended for patients with diabetes and for patients with suspected iatrogenic Cushing’s Disease.
There are a few treatment options. In the case of adrenal tumor Cushing’s disease, surgery is recommended to remove the tumor, if surgery is needed it may be beneficial to seek out a dog bed that helps with heal time, BuddyRest offers a dog bed that does just that. However, this comes with the risk of anesthetic complications and the risk of developing too-low levels of cortisol immediately following surgery. Malignant tumors can also spread to other parts of the body, and adrenal tumors do not usually respond well to oral medications.
If your dog has PDH, then oral medication is prescribed. The most commonly recommended medication is called Vetoryl (aka trilostane), and it helps to stop the adrenal glands from producing cortisol. Vetoryl works best when given on a twice-daily basis, and if it is working well, then your dog’s increased thirst, urination, and appetite should be controlled. Careful monitoring of cortisol levels is important because, in rare cases, Vetoryl can overly suppress the adrenal glands and cause the opposite condition. This state of too-low cortisol levels is called Addison’s disease. If your dog is lethargic or experiencing vomiting and diarrhea while taking Vetoryl, then contact your veterinarian right away.
If your dog with PDH is showing any neurologic signs like tremors or seizures, then there may be a large pituitary tumor called a macroadenoma, and Vetoryl alone may not help resolve their clinical signs. Radiation therapy can help shrink the tumor so that the medication may work more effectively. In some cases, your dog may be able to stop Vetoryl completely after several months! Long term prognosis for these patients is very good.
Cushing’s Disease can be a frustrating illness because it can take some time to definitively diagnose it, and it can be difficult to see your dog experience some of the clinical signs. It is important to seek treatment right away so that your best friend can go back to normal, and routine monitoring is vital to make sure that your dog will have the best outcome!
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Meet The Author
Veterinarian
Erica has worked in the veterinary field since 2006, starting out as a veterinary technician before graduating from the UF College of Veterinary Medicine in 2013. As a general practitioner in an animal hospital, she has many interests and is especially interested in dermatology, cardiology, internal and integrative medicine.
