Cushing's Disease in Dogs

A complete guide on Hyperadrenocorticism for dog owners

This article is written by Pet Circle's qualified veterinarian, Dr Carla Paszkowski, BVSc (Hons)

Has your dog been diagnosed with Cushing's Disease? Or perhaps you are a prospective puppy owner researching your favourite dog breed, but have discovered they are a breed prone to developing Cushing's and want to equip yourself with some knowledge. This guide should provide you with everything you need to know about Cushing's Disease in dogs.

1. What is Cushing's Disease?

2. Which dog breeds are prone to Cushing's Disease?

3. Symptoms of Cushing's Disease

4. Diagnosis of Cushing's Disease

5. Treatment of Cushing's Disease

6. The Best Diet for Cushing's Disease

7. Supplements for Cushing's Disease

What is Cushing's Disease in Dogs?

The different types of Cushing's Disease

There are three main forms of Cushing's Disease, correlating purely to where the cause of the disease sits anatomically:
- 1. Pituitary Dependent Cushing's. This is the most common form, seen in about 80-90% of dogs with Cushing's. The pituitary gland is a pea sized gland at the base of the brain, and one of its functions is to send signals to the adrenal glands. If the pituitary gland is over active, the otherwise normal adrenal glands will respond to this overstimulation. Usually, a tumour in the pituitary gland causes its hyperactivity - but the tumour itself is oftentimes benign.
- 2. Adrenal Dependent Cushing's. This type of Cushing's is caused by overactive adrenal glands. In most cases, the overactivity is caused by a tumour in an adrenal gland, which causes it to expand and produce excess cortisol. Around 15% of dogs with Cushing's have this type.
- 3. Iatrogenic Cushing's. Iatrogenic typically means 'caused by medication'. This type of Cushing's occurs after a dog has been treated with corticosteroids for a long time.

Did you know? Cortisol is normally used by the body to respond to stress, keep bodyweight in check, fight infections, and maintain blood sugar levels. However, like many hormones, too much or too little Cortisol can cause problems.

Dog breeds that are prone to Cushing's Disease

Symptoms of Cushing's Disease

Diagnosis of Cushing's Disease in dogs

How to tell if your dog has Cushing's Disease

Diagnosis of Cushing's Disease requires a veterinary examination and blood tests. Your veterinarian will be able to inspect your dog's appearance, feel their abdomen, listen to their heart, and perform blood and urine tests.

Blood Tests for Cushing's

While there is no single test that can diagnose 100% of cases, your vet will likely recommend a combination of the following tests:
- Baseline bloodwork (CBC / biochemistry)
- Urinalysis
- ACTH stimulation test - this involves testing the cortisol levels in the blood before and after giving an injection of adrenocorticotropic hormone (ACTH). In a healthy dog, the cortisol level should rise a little. In a dog with Cushing's, the cortisol will start high and rise even higher.
- Low-Dose Dexamethasone Suppression Test - for this, the dog receives an injection of dexamethasone (a steroid). In a healthy dog, the cortisol level will drop because the steroid suppresses adrenal activity. In a dog with Cushing's, the cortisol levels fail to decline.
- High-Dose Dexamethasone Suppression Test
- Urine cortisol to creatinine ratio
- Abdominal ultrasound (this helps observe any changes in the liver and adrenal glands)
- CT or MRI (this can help identify pituitary tumours)

Treatment of Cushing's Disease in dogs

Photo: @windrosestar

The good news is that Cushing's in dogs can be easily treated. However, the type of treatment your dog needs depends on the type of Cushing's Disease your dog has.

If a Pituitary tumour is the cause, treatment can be a little complicated but is usually managed with medication. (Brain surgery to remove a tumour is not the norm in veterinary medicine!) Either trilostane or mitotane might be prescribed for daily administration.

If an Adrenal tumour is the cause, the best treatment is a surgery to remove the tumour. If the entire tumour can be removed, there is a good chance that the dog will return to normal health.

If Iatrogenic Cushing's is the cause - ie, caused by administration of steroids - the treatment involves discontinuing the steroids. This often results in a recurrence of the original condition that the steroids were treating, but over time you and your vet may be able to make adjustments in which a balance can be found.

As discussed earlier, a pituitary tumour is the most common cause. A dog with pituitary dependent Cushing's can live a normal active life with medication, which moderates steroid production. It is important not to give too much of your dog's Cushing's medication because if steroid levels drop too low, you may push your dog into Addison's Disease (hypoadrenocorticism).

Ongoing care with regular vet check ups will be necessary to monitor your dog's progress and response to medication.

Home Care for a Dog with Cushing's

In addition to giving your dog their medication daily, you will need to monitor your dog's drinking and urination. It's important never to restrict your dog's access to water, and your vet may recommend keeping a water diary to note how much your dog is drinking. It's also important to feed your dog an appropriate food and limit treats and table scraps - read more about this below.