Cushing Disease in Dogs

What is Cushing’s disease?

Cushing’s disease (CD) also known as hyperadrenocorticism is a common hormone disease diagnosed in dogs. This disease has been reported to affect 1 to 2 /1,000 dogs/year.¹ It is a condition in which the adrenal glands (small glands found near the kidneys) make too much cortisol (stress hormone). In 80-85% of cases, this can be a result of a benign tumor growing on the pituitary gland in the brain that then releases excessive amounts of a stimulating hormone that results in an overstimulation of the adrenal glands.² In the other 10-20% of cases, it is caused by a tumor growing on the adrenal glands that results in the overproduction of hormones.³ Moreover, some cases of CD can be caused by the long-term use of steroids, known as iatrogenic Cushing’s, which is reversed with slow monitored removal of the medication.

Symptoms and breeds commonly associated with Cushing’s

The most common symptoms are excessive thirst, urination, and a ravenous appetite, where the dog seems constantly hungry and may beg for or steal food (more than normal). But many other symptoms can be present, such as chronic skin issues with very thin skin that is fragile and prone to bruising and hair loss that is pronounced on the trunk and tail, which results in a “rat tail” appearance. Dogs may gain excessive weight with fat depositing in the belly, resulting in a pot-bellied appearance. Other signs are frequent urinary tract infections and lethargy due to muscle loss. Dogs over 7 years of age have the highest chance of developing CD.⁴ Some breeds are predisposed to developing CD, like the Bichon Frisé, Border Terrier, Miniature Schnauzer, Lhasa apso, Yorkshire Terrier, Staffordshire Bull Terrier, Jack Russell Terrier, Miniature Poodles, and Dachshunds.⁴

Diagnosis

If you suspect your dog may have CD, you should see your veterinarian for evaluation and diagnostics. This can include basic bloodwork to rule out other diseases that may be present with similar symptoms. Then if CD is suspected, there are specific blood tests your veterinarian may run to determine if the disease is present.

These include blood tests:

• ACTH Stimulation Test (Preferred): The most common diagnostic test for Cushing's disease is the ACTH stimulation test. In this test, a baseline blood cortisol level is measured, and then a synthetic hormone called ACTH (adrenocorticotropic hormone) is administered. After a set period, cortisol levels are measured again. Dogs with Cushing's disease often show an exaggerated increase in cortisol levels in response to ACTH.
• Low-Dose Dexamethasone Suppression Test (LDDS): This test involves administering a low dose of dexamethasone (a synthetic cortisol-like medication) to your dog and then measuring cortisol levels. In Cushing's-affected dogs, cortisol levels remain elevated, while in healthy dogs, they should decrease.
• Urine Cortisol-to-Creatinine Ratio: In some cases, a urine test may be used to measure the ratio of cortisol to creatinine in the urine. Elevated ratios can suggest Cushing's disease.

If Cushing's disease is suspected, then your veterinarian may recommend additional tests to determine the specific cause of the condition.

These tests include:

• Adrenal Hormone Testing: This can involve measuring hormone levels, such as aldosterone and sex hormones, to differentiate between pituitary-dependent and adrenal-dependent Cushing's disease.
• Imaging Studies: In some cases, imaging studies like abdominal ultrasound or MRI may be performed to visualize the adrenal glands and identify any tumors or abnormalities. This is particularly useful in differentiating between pituitary and adrenal forms of the disease.
• Low-Dose ACTH Stimulation Test (LDDS): This test is similar to the standard ACTH stimulation test but uses a lower dose of ACTH. It can help differentiate between the pituitary and adrenal forms of Cushing's disease.
• High-Dose Dexamethasone Suppression Test (HDDS): This test is less commonly used than the LDDS test and may be employed if other test results are inconclusive.
• Endogenous (internal) ACTH Measurement: In some cases, measuring endogenous ACTH levels directly in the blood may be necessary to differentiate between pituitary-dependent and adrenal-dependent Cushing's disease.

Treatment

In some cases, treatment may include surgery or radiation therapy aimed to reduce or eliminate the offending tumor, but often the condition can be treated with medical management alone.⁶ Medical management of Cushing's disease is using drugs that suppress the production of cortisol in the adrenal gland.

Prognosis

The prognosis for dogs with Cushing's disease is dependent on several factors and can vary. As with many diseases, early diagnosis and intervention tend to yield better outcomes. Dogs with pituitary-dependent Cushing's disease, the more common form, often respond well to treatment, which can include medications, surgery, or radiation therapy. Regular monitoring by a veterinarian is crucial to ensure that the condition is effectively managed and complications, such as diabetes and infections, are addressed promptly. The age and overall health of the dog can also influence the prognosis, with older or medically compromised dogs facing greater challenges. However, with owner compliance, proper treatment, and ongoing veterinary care, many dogs with Cushing's disease can enjoy an improved quality of life and potentially live comfortably for an extended period. Consulting with a veterinarian is essential to determine the best course of action and prognosis for a specific dog with Cushing's disease.

Reference

1. de Bruin, Christiaan, et al. 2009. Cushing’s disease in dogs and humans. Hormone Res 71(1):140-143.
2. Galac, Sara, et al. 2010. Effects of trilostane on the pituitary-adrenocortical and renin–aldosterone axis in dogs with pituitary-dependent hypercortisolism. Vet J. 183(1):75-80.
3. Labelle, P., et al. 2004. Indicators of malignancy of canine adrenocortical tumors: histopathology and proliferation index. Vet Pathol. 41(5):490-497.
4. Schofield I, Brodbelt DC, Niessen SJM, et al. 2021. Frequency and risk factors for naturally occurring Cushing's syndrome in dogs attending UK primary-care practice. J Small Anim Pract. 63(4):265-74.
5. Thompson, TB. What Causes Cushing’s Disease in Dogs? Your Vet Friend’s Simple Guide - Your Vet Friend. Your Vet Friend, 6 Apr. 2022, https://yourvetfriend.com/cushings-disease-in-dogs/.
6. Sanders, K., H. S. Kooistra, and S. Galac. 2018. Treating canine Cushing’s syndrome: Current options and future prospects. Vet J. 241 241:42-51.

About the author: Dr. Katy Miller works as the Director of Veterinary Services at BSM Partners. She previously served for 11 years as the Director of Dog and Cat Health and Nutrition for Mud Bay. Prior to specializing in nutrition, she worked for five years in private practice and seven years in emergency medicine. She is also a competitive 3-day eventer, licensed falconer, and claims only 2 (Golden and Mini Doxie) of their nine dogs.

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