Cushing’s Disease in Dogs

Cushing’s Disease in Dogs

It’s said that a little bit of stress can be beneficial, but surely most will agree that too much stress is never good. Our pets – and their bodies – are certainly no exception to the rule. 
The body’s response to stress is primarily controlled by the adrenal glands, of which every pet has a pair. One gland sits next to each kidney. 

During times of stress, the brain stimulates the adrenal glands to produce the hormone cortisol, which regulates metabolism (the conversion of food and body reserves into energy). 

Under normal circumstances, increased cortisol in the blood causes the brain to reduce stimulation to the adrenal glands, ultimately reducing cortisol production. This feedback loop ensures that cortisol is released only in short bursts. 

Cortisol production under normal circumstances

What is Cushing’s disease?
Cushing’s disease is the overproduction of cortisol. Affected dogs are exposed to cortisol over a long period of time, rather than only during short periods of stress.
Cushing’s disease is most common in dogs aged 7 years and older. Although dogs of any breed may develop the disease, breeds at higher risk include the miniature Schnauzer, Jack Russell terrier, Bichon Frise and Yorkshire terrier. 

Cushing’s disease types
There are two types of Cushing’s disease: pituitary-dependent (more common) and adrenal-dependent (less common).

Pituitary-dependent Cushing’s disease arises due to a tumour in the brain. The presence of the tumour means the stimulation to the adrenal glands is constant and does not reduce even when there are large amounts of cortisol in the blood.

Adrenal-dependent Cushing’s disease arises due to a tumour in one of the adrenal glands that constantly produces cortisol (the brain is unaffected). In response to high cortisol levels, the brain reduces stimulation to the adrenal glands, but to no avail.

What are signs of Cushing’s disease?
Common signs of Cushing’s disease are listed below. Affected dogs may not show all of these signs. 
•    Lethargy
•    Increased panting
•    Increased appetite
•    Increased drinking and urination
•    Hair loss, especially on body and tail
•    Thinning of skin
•    Firm, crusty plaques on skin
•    “Pot-bellied” appearance

Note the pot belly and hair loss on the body of this dog with Cushing’s disease. (Image source: VIN)

How is Cushing’s disease diagnosed?
Vets frequently start by taking your dog’s history, performing a thorough physical examination and running baseline blood and urine tests. Results may hint towards Cushing’s disease, but further testing is needed for confirmation as many other diseases can present similarly.
Specialised blood testing is required to confirm the diagnosis of Cushing’s disease. Once Cushing’s disease is confirmed, further testing may be performed to differentiate pituitary- and adrenal-dependent forms. An ultrasound scan of your dog’s abdomen might also reveal an adrenal tumour, or enlargement of both adrenal glands (suggesting overstimulation from the brain, i.e. pituitary-dependent disease).

How is Cushing’s disease treated?
Both forms are often treated with trilostane, a medication that suppresses excessive cortisol production. In some cases of adrenal-dependent Cushing’s disease, surgery to remove the affected gland may be an option, although this often requires referral to a specialty facility.

Treatment with trilostane cannot cure Cushing’s disease, however, medication is crucial in prolonging the lives of affected dogs and safeguarding their quality of life. Affected dogs often improve within a week of starting treatment, although associated skin conditions may take months to resolve (particularly for hair to grow back).  
Thank you for reading and we hope the information in this article has been useful for both you and your pet. Please speak with your veterinarian if you have specific questions pertaining to your pet’s health.