My dog has Cushing’s disease. What does this mean?
Cushing’s disease, also known as hyperadrenocorticism, is a condition that develops in dogs and uncommonly, in cats too. Although this sounds like a complicated medical condition, in this article, we’ll unravel its meaning. Keep reading to learn more about its signs, diagnosis, and treatment!
What does ‘hyperadrenocorticism’ mean?
The adrenal glands secrete hormones and have two distinct areas: the cortex, which is responsible for steroid production, and the medulla, which is responsible for the production of adrenaline. Both hormones are required by the body when under stress. Animals that suffer from Cushing’s disease have an adrenal cortex that is producing too much steroid hormone. So, hyper- (high function of), -adreno (the adrenal), -corticism (cortex).
One of the most widely known hormones produced by the adrenal glands is cortisol, also known as cortisone. This hormone is often referred to as the stress hormone and is responsible for many physiological activities and influences the production and release of other hormones. Any excess in the production of cortisol can result in serious health problems in canine patients.
What are the signs of Cushing’s disease in dogs?
Patients with this disease have too much cortisol whizzing around their bodies. Although some is vital for life and essential to function in stressful circumstances, too much of this hormone causes a range of common signs in dogs such as:
- Drinking excessive amounts of water, in turn causing increased urination.
- Increased appetite, often accompanied by weight gain.
- Thinning of the haircoat.
- Change of shape - pendulous tummy and loss of muscle.
In cats, it can cause the above symptoms, but more commonly causes skin fragility (easy to bruise and tear) and diabetes. In fact, diabetic cats that aren’t responding well to treatment should be screened for hyperadrenocorticism.
What causes Cushing’s disease in dogs?
There are essentially 3 types of hyperadrenocorticism observed in dogs, each with different causes, prognosis, and treatment approaches. Accurate identification of the type of Cushing’s and the specific cause is important for a more targeted treatment and successful management of the condition.
In over 80% of cases in dogs and nearly 100% of cases in cats, hyperadrenocorticism is caused by a benign tumor of the pituitary gland which is situated in the lower part of the brain. This gland is responsible for regulating several different hormone levels and stimulates the adrenal glands to produce cortisol. In the case of Cushing’s disease, the pituitary gland is overactive, in turn causing the adrenal glands to secrete too much cortisol. This is called pituitary-dependent disease.
In a smaller number of patients, tumor growth in the adrenal glands, which can be benign or malignant, is another possible cause of Cushing’s disease in dogs. The pathophysiology of this type of Cushing’s disease is more straightforward, as the tumor produces cortisol uncontrollably, resulting in the hormonal problem.
This form is called adrenal-dependent disease.
For this reason, it’s important to diagnose the type of tumor causing Cushing’s disease. This can be done by a combination of further blood tests and/or imaging of the adrenal glands via an ultrasound scan.
The last type of hyperadrenocorticism in dogs is called iatrogenic Cushing’s disease. This is caused by the prolonged use of corticosteroids, either administered orally or injected into the dog at a regular frequency. This commonly happens in dogs suffering from a different health problem which requires the use of corticosteroids as treatment. Systemic corticosteroids have the same physiological effect as cortisol in the dog’s body. Prolonged use of corticosteroids results in Cushing’s disease due to the accumulation of cortisol in the dog’s system. Since the cortisol is administered exogenously, the pituitary gland cannot control the increase in cortisol levels.
How is Cushing’s disease diagnosed in dogs?
Cushing’s disease is most common in middle-aged to older dogs of certain breeds: Miniature Poodles, Dachshunds, Boxers, Boston Terriers, and Beagles.
Your vet may have a suspicion based on the pet’s breed and symptoms. However, a routine blood test will often show certain changes such as a rise in liver enzymes, particularly one named ALKP.
Urine samples often give certain clues too, but to make a definitive diagnosis, a blood test to measure cortisol levels must be performed. A single (baseline) cortisol level isn’t enough to make a diagnosis because pets are often stressed when blood is being taken. This can lead to a falsely elevated result! For this reason, an ACTH stimulation test is carried out to see how the adrenal gland can react in response to stimulation. If the result is high, Cushing’s disease is confirmed.
How is Cushing’s disease treated?
Pituitary-dependent Cushing’s disease is very treatable. Normally it will be controlled with a pill given once or twice daily. Your pet will be monitored closely when first on treatment to ensure the correct dose is established. After that, they will probably be monitored every 3 or 4 months via a simple blood test and physical exam.
The prognosis is fair so long as the treatment is continued. It should be noted that this is a lifelong condition so medication is taken on an ongoing basis. A newer form of treatment involves radiation therapy of the overactive part of the pituitary gland. The treatment is showing promising results, but it needs to be carried out and reviewed at a specialty center.
Adrenal-dependent Cushing’s disease, though much less common, is more concerning because it’s caused by a potentially aggressive tumor. Although the incidence of this disease is low, treatment normally requires surgery to remove the tumor. This should be carried out by an experienced surgical team due to the complexity of these tumors.
Of all the types, iatrogenic Cushing's can be the easiest to address and manage. Gradual reduction of the corticosteroid administration is often enough to control the activity of the adrenal glands and balance the cortisol production in the body. However, this must be carefully balanced with the pet's other health conditions that may still require some type of steroid treatment.
In cats, treatment may involve the same medical therapy given to dogs. Cats, however, can be less straightforward to treat than dogs, as they are often also diabetic.
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