Written by Dr Larry Kraitzick of Bruma Lake Veterinary Clinic
Cushing’s disease is a serious disorder affecting the body’s levels of the hormone cortisol (cortisone). Produced by the adrenal glands, this hormone is essential for controlling things like stress response (fight or flight), glucose metabolism, blood pressure and inflammation. Cushing’s disease is when there’s too much of the hormone. You may have heard about it occurring in people, but dogs can develop it too – and, if left untreated, it can be life-threatening to your canine companion.
What causes Cushing’s disease?
Cushing’s disease (or hyperadrenocorticism), has several possible causes. It can be a result of giving a dog too much cortisone (exogenous), or a result of the body itself producing too much cortisone (endogenous). In exogenous Cushing’s, slowly withdrawing the cortisone will result in the symptoms subsiding (this is why you should never abruptly stop giving your dog cortisone medication).
Most cases in dogs have an endogenous cause and originate either in the pituitary gland or adrenal gland or glands.
About 80-85% of Cushing’s is pituitary-dependent, meaning it’s triggered by a tumour on the pituitary, a pea-sized gland at the base of the brain. The pituitary produces many different hormones, including adrenocorticotropic hormone (ACTH). A pituitary tumour may result in overproduction of ACTH, which then travels via the bloodstream to the adrenal glands where it acts as a signal to produce cortisol (a type of cortisone).
In the other 15-20% of Cushing’s dogs, a tumour in one or both adrenal glands produces excess cortisol.
Cushing’s disease typically occurs in middle-aged to older dogs and smaller breeds. However, it can occur in any age and in larger breeds.
Symptoms and diagnosis of Cushing’s disease
This disease develops slowly, and the early signs aren’t always noticed. Some of the symptoms in dogs include:
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increased thirst
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increased urination
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increased appetite
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reduced activity
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excessive panting
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thin or fragile skin
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hair loss
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recurrent skin infections
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enlargement of the abdomen, resulting in a “pot-bellied” appearance
We use blood tests to diagnose Cushing’s disease and to differentiate between disease caused by the pituitary or the adrenals. We also use ultrasound to help detect a tumour on an adrenal gland.
Can Cushing’s disease be treated?
We usually treat both adrenal- and pituitary-dependent Cushing’s disease with medication. The only way to “cure” the disease is to remove the tumour (if that was the cause). In the adrenal type, this will only be curative if the tumour hasn’t spread.
However, because of the complexity and risks of the surgery, most adrenal tumours are still treated with medication. Surgical techniques to remove the pituitary gland can be carried out, but surgery isn’t a widely available option.
There are several treatment options, but the best tolerated is Trilostane, a drug that interferes with the production of cortisol by the adrenals. You should discuss treatment with your veterinarian to find an option that’s best suited to your dog.
Frequent blood tests are usually required in the first few months after starting treatment, and then every few months after that, depending on the dog’s response to treatment and tolerance to the medication.
What’s the prognosis?
Left untreated, Cushing’s disease will progress. As excess cortisol is immunosuppressive, Cushingoid dogs are prone to various infections. They’re also predisposed to developing hypothyroidism, pancreatitis, diabetes, seizures, hypertension, congestive heart failure, blood clots (thromboembolism), and liver and kidney failure. Many of these dogs are at risk of early euthanasia due to incontinence resulting from increased water consumption.
The short-term prognosis with treatment is very good. In most cases, symptoms of Cushing’s disease fully resolve over the course of 4-6 months. Excess drinking and urinating stop quickly. It may take several months for hair and coat improvement to be observed. Dogs generally are more comfortable after the disease is under control and may live happily for years.
In some rare cases dogs become very uncomfortable if arthritis, allergies, or other inflammatory conditions are unmasked once the excess cortisol is removed
Another consideration relates to pituitary tumours themselves. As the tumour in the pituitary gland continues to grow, neurologic signs from damage or pressure on structures in the brain may present over time.
The goal of treatment is to improve quality of life and hopefully lengthen life. However, except in a situation where an adrenal tumour can be completely removed, Cushing’s disease isn’t something from which a dog recovers – it’s managed, not cured. Whether treated or not, most dogs will die within a few years of diagnosis, although not necessarily due to Cushing’s itself. Again, that’s because most Cushing’s patients are elderly and have other concurrent health issues. Nonetheless, hyperadrenocorticism is a serious condition, and maintaining a dog with Cushing’s disease requires vigilance and commitment on the part of the owner.
Please note, I’ve tried to keep this article as concise as possible. This is a complicated disease. Each case and every individual is different and requires a different approach. Always consult your veterinarian if your dog seems unwell.
