Cushing’s disease, or hyperadrenocorticism, is a common endocrine disorder in dogs. Symptoms can vary, and diagnosis is sometimes difficult. Fortunately, Cushing’s is treatable in most cases.
Hyperadrenocorticism refers to a hyperactive adrenal gland. The adrenal glands are located near the kidneys. They produce several hormones, including cortisol (affecting how the dog responds to stress and disease), and adrenaline (for the “fight or flight” response). Cushing’s is usually seen in older dogs, both male and female, and can affect any breed. The classic symptoms are due to overproduction of cortisol by one or both adrenal glands.
The symptoms include: Drinking a lot (excessive thirst); urinating a lot or having accidents in the house; increased appetite; infections (especially skin and bladder); “pot belly” appearance; lethargy or decreased activity level; panting even when resting; weight gain; hair loss or thinning fur; and poor healing.
There are two sub-types of Cushing’s disease in dogs:
Pituitary-dependent hyperadrenocorticism (PDH). A small tumor develops in the pituitary gland in the brain. This tumor usually does not cause any symptoms in the brain, but overproduces a hormone called ACTH, which stimulates the adrenals to overproduce cortisol. PDH is more commonly seen in small-breed dogs.
Adrenal tumor (AT). A tumor develops in one of the adrenal glands, and overproduces cortisol. AT is more commonly seen in large-breed dogs.
Diagnosis
Diagnosis of Cushing’s may be fairly straightforward, or may be challenging. Routine blood and urine tests are run first. A few clues that may be seen include elevated liver enzymes, dilute urine, and evidence of a urinary tract infection. If your veterinarian is suspicious of hyperadrenocorticism, a variety of more advanced tests may be required. None of the tests is perfect, so several may need to be run. Advanced tests include:
Urine cortisol/creatinine ratio. This is used as a screening test and measures cortisol in the urine. If the test result is normal, the dog does not have Cushing’s. If it is elevated, the dog may or may not have Cushing’s, and further tests must be run.
ACTH stimulation test. In this test, a blood sample is taken, then an injection of synthetic ACTH is given, and a second blood sample is taken an hour later. The “before” and “after” levels of cortisol are measured and compared. A dog with Cushing’s will show an exaggerated response.
Low-dose dexamethasone suppression test. In this test, a blood sample is taken, then an injection of dexamethasone is given, and more blood samples are taken after 4 and 8 hours. Again, the “before” and “after” cortisol levels are compared. In a normal dog, the “after” levels will be decreased, but a dog with Cushing’s will not show a decrease.
Abdominal ultrasound. This test is run to differentiate PDH from AT. Typically in PDH, both adrenals are enlarged, while in AT, the tumor is visible in one adrenal while the other adrenal is shrunken.
Treatment
After we have diagnosed hyperadrenocorticism and determined whether it is due to PDH or AT, treatment can begin. The goal of treatment is to get the dog back to normal activity, appetite, water intake and urination. For an adrenal tumor, the mainstay of treatment is surgery to remove the tumor. Pituitary-dependent Cushing’s cannot be cured, but can be managed long-term, like diabetes or heart disease. Several medications are commonly used:
Mitotane (Lysodren). Mitotane kills cells of the adrenal gland. Treatment is in two phases: the induction phase (the medication is given twice daily to kill off many adrenal cells), and the maintenance phase (the medication is given once or twice per week to prevent relapse of symptoms). Mitotane is potentially dangerous, so the dog must be monitored very closely during the induction phase, which lasts 5-14 days. Side-effects of mitotane are vomiting, diarrhea, lethargy and loss of appetite. Mitotane can also be used for treatment of an adrenal tumor if surgery is not feasible.
Trilostane (Vetoryl). Trilostane inhibits formation of cortisol. It is given on a daily basis. Side effects include loss of appetite, vomiting, and-rarely-sudden death.
Ketoconazole. Ketoconazole is typically used as an anti-fungal, but it also inhibits formation of cortisol. Side effects include vomiting, diarrhea, and liver toxicity.
Selegiline (L-deprenyl or Anipryl). Selegiline is typically used for canine cognitive dysfunction (“doggy Alzheimer’s”), but may be helpful for certain cases of PDH.
Although all of the medications have potential side effects, Cushing’s is usually successfully treated. Dogs with Cushing’s can generally have a normal life-span with a good quality of life.
Sources:
Wendy Brooks, DVM: What Exactly is Cushing’s Disease. Veterinary Partner
Wendy Brooks, DVM: Treatment: Pituitary Cushing’s Syndrome. Veterinary Partner
Donald Plumb, Pharm D: Plumb’s Veterinary Drug Handbook, WIley, 2008.
Disclaimer: The above article is for general education purposes. It is not intended to diagnose or treat an individual pet. If you have questions or concerns about your pet, please contact your local veterinarian.
