Cushing’s disease is also known as hyperadrenocorticism and is caused when the dog’s body produces an excessive amount of the hormone cortisol.
Cortisol is an important hormone that the body needs to function properly. However, excessive amounts can cause all sorts of serious problems for the dog including increased thirst, increased urination, skin changes, weight gain and a characteristic “bot belly” appearance.
This is a fairly common condition in middle-aged to older dogs.
Do you think your dog could have Cushing’s disease? In this article, we will provide all the important information that you need to know about this disease, including what causes it, the common symptoms, diagnosis and treatment options.
What is Cushing’s Disease?
Cushing’s disease is due to the excessive production of the hormone cortisol. Cushing’s disease can be caused by a tumor on the adrenal glands on the kidneys or the pituitary gland in the brain, which causes the cortisol levels to skyrocket.
Cortisol is an extremely important steroid hormone in the dog’s body. This hormone is produced by the adrenal glands, two small glands located on the kidneys.
The production of cortisol by the adrenal glands is controlled by another hormone called ACTH, which is produced by the pituitary gland, in the brain. These glands and hormones work together to keep cortisol levels in the blood within a normal range. (1)
To understand Cushing’s disease, it is important to learn a bit more about the normal role of cortisol in the dog’s body.
What Is The Role Of Cortisol In The Dog’s Body?
Cortisol is often referred to as the “stress hormone” because it plays a big part in the body’s normal stress response. However, it also plays an important role in controlling blood sugar levels, regulating metabolism rate, controlling blood pressure and helps control the salt and water balance too.
When a dog becomes stressed or scared, the “fight or flight” response is activated, causing a surge of hormones including cortisol.
This is a survival mechanism that allows mammals to react quickly to a perceived threat.
As the body goes into survival mode the heart rate and breathing rate increase, and the blood pressure goes up.
The airways open up to increase oxygen intake, more energy (glucose) is released into the bloodstream and the body’s metabolism rate increases.
All these actions would help a scared dog to run away from danger. As the body thinks it on high alert, cortisol also restricts functions that it deems nonessential in an emergency, such as growth and reproduction processes and reduces the immune response.
This is all a totally normal response for a dog in a stressful moment, and once the “danger” has passed the cortisol levels drop and the dog’s body soon returns to the calmer “rest and digest” response.
What Happens During Cushing’s Disease?
If a dog has Cushing’s disease, then too much cortisol is being produced. This leads to the body staying in a “stressed” state with the “fight or flight” response constantly switched on, which can quickly take a toll on the dog.
In the long term, this can cause lots of health problems for the dog including skin changes and infections, reduced immune system function and increase dog’s risk of developing diabetes.
What Causes Cushing’s Disease?
So you already know by now that Cushing’s disease is due to very high levels of cortisol in the blood. There are three main causes of this disease in dogs:
- A tumor on the pituitary gland
The most common (85-90%) cause of Cushing’s disease is a benign tumor on the pituitary gland in the brain.
- A tumor on the adrenal gland
Cushing’s disease may also be caused by a benign or malignant tumor of the adrenal gland on the kidney. (10-15%)
- Administration of too much corticosteroid medication
Corticosteroid medication is often used to treat dogs with allergies or immune disorders. Long term use of this medication can put the dog at high risk of developing Cushing’s disease.
It is important to find out what has caused the Cushing’s disease, as it may affect the dog’s treatment options and long term prognosis. (2)
What Are The Signs Of Cushing’s Disease In Dogs?
Regardless of what has caused Cushing’s disease the clinical signs in affected dogs are all the same. The most common signs of Cushing’s disease in dogs include:
- Increased thirst (polydipsia)
- Increased urination (polyuria)
- Increased appetite (polyphagia)
- Weight gain
- Muscle loss
- Abdominal enlargement or “pot-belly” appearance
- Increased panting
- Recurrent urinary tract infections
- Thinning of the skin and hair loss
- Recurrent skin infections
- Calcification of the skin
Are Some Dog Breeds More At Risk Of Cushing’s Disease?
Any breed of dog can develop Cushing’ disease but some dog breeds do appear to be at a higher risk of developing this condition than others. Breeds in which Cushing’s disease is more commonly diagnosed include:
- Miniature poodles
- Boston terriers
- Yorkshire terriers
- Staffordshire terriers
Research has found some other predispositions with this condition. Female dogs are around 3 times more likely to suffer from Cushing’s than male dogs and large-breed dogs are more likely to have a tumor on the adrenal gland.
How Is Cushing’s Disease Diagnosed?
This disease is not always easy to diagnose. Some dogs may show all the classic clinical signs, but the diagnostic tests come back negative. Other dogs may only show a few subtle signs of the condition, which can be similar to many other diseases such as hypothyroidism or diabetes.
A veterinarian may suspect Cushing’s disease after a full history has been taken and a complete physical examination has been performed, but further tests are needed to confirm the diagnosis.
Usually, a combination of blood tests, urine tests and ultrasound scans of the abdomen (tummy) are used to diagnose this condition. Further imaging such as an MRI or CT of the brain is needed to check if there is a pituitary gland tumor present.
What Blood Tests Are Needed To Diagnose Cushing’s Disease?
Routine blood tests are often the starting point to check organ health and underlying conditions. These blood tests are commonly run in the vet clinic and include biochemistry (organ health, calcium and salt levels) and hematology (red and white blood cells).
These tests are important and useful, and in pets with Cushing’s disease common findings include:
- Increased liver enzymes
- Increased cholesterol
- Increased glucose levels in the blood (hyperglycemia)
- Low levels of sodium, and high levels of potassium in the blood
However, these results aren’t specific enough to diagnose Cushing’s disease, as other conditions and diseases may cause similar changes in routine blood tests. Furthermore, there is no single test or combination of tests that are100% accurate to diagnose Cushing disease.
Therefore, furthermore specialized blood tests need to be carried out, but even those aren’t 100% accurate! That is why sometimes Cushing’s disease may be difficult to diagnose, and sometimes veterinarians need to repeat tests.
The most commonly used dynamic blood tests used to diagnose Cushing’s disease in dogs include:
- ACTH stimulation test
- Low dose dexamethasone suppression (LDDS) test
These tests involve the dog being admitted into the hospital for the day. An initial blood sample is taken from the dog to measure the baseline level of the hormone cortisol.
An injection of ACTH or dexamethasone is administered to the dog, and further blood samples are taken at specific times later in the day to measure how the level of cortisol changes. These results can help the veterinarian diagnose Cushing’s disease.
What Are The Treatment Options For Cushing’s Disease?
Cushing’s can be treated with medication, surgery or radiation therapy.
Usually, Cushing’sdisease is treated medically, with a daily medication given to the dog to reduce the cortisol levels in the dog’s body and help control the symptoms.
The medication needs to be given to the dog for the rest of its life to manage the disease. Sometimes surgery or radiation therapy may be recommended in some specific cases.
This medication is available in capsule form and is given once or twice daily, depending on the dose that the dog requires. Blood tests need to be performed at regular intervals to check if the medication is working.
Studies have shown that after several months of treatment partial or complete control of the condition occurs in >75% of cases. There are some potential side effects of the medication.
The product datasheet states that the most common possible side effects include reduced appetite, vomiting, dullness, diarrhea, and weakness. Giving too much medication could cause a serious emergency medical condition called hypoadrenocorticism.
In some cases of Cushing’s disease surgery may be needed to control the condition. Adrenal tumors on the kidneys, or pituitary tumors in the brain, causing Cushing’s disease can sometimes be surgically removed.
However, the surgery is pretty complicated and requires a specialist surgeon and specialist anesthetist, and usually, this is only completed in referral hospitals. The veterinarian should discuss all the potential risks of the surgery.
Radiation uses beams of intense energy to kill cancer cells. Radiation treatment may be an option for some dogs with pituitary tumors. However, medication may still be necessary for a few months following the procedure. (4)
Radiation therapy is usually only available from a specialist veterinary oncologist in a referral hospital.
What Is Hypoadrenocorticism?
Hypoadrenocorticism, also known as Addison’s disease, is caused by lower than normal production of hormones like cortisol by the adrenal glands.
A dog with Cushing’s disease can develop hypoadrenocorticism if it’s dose of medication (Trilostane) is too high, or accidentally has an overdose. If a dog doesn’t have Cushing’s disease, then they can just develop hypoadrenocorticism randomly out of the blue, and most of the time the cause is unknown (idiopathic). (5)
Other causes include infections, tumors or trauma of the adrenal glands. Symptoms are quite unspecific and can wax and wane. Common signs include decreased appetite, vomiting, diarrhea, weight loss, and weakness.
Dogs being treated for Cushing’s disease need to be closely monitored for signs of hypoadrenocorticism, and seek veterinary help immediately as it is a medical emergency.
Cushing’s Disease In Dog: Conclusion
Cushing’s disease is a serious condition that needs lifelong treatment and regular monitoring.
The most common (85-90% of cases) cause of Cushing’s disease is a benign tumor on the pituitary gland in the brain. However, it can also be caused by an aggressive brain tumor, a tumor on the adrenal gland of the kidneys or from receiving too much corticosteroid medication.
Most dogs are successfully treated using a daily medication called trilostane, but other options can include surgery or radiation therapy.
This condition does take some dedication from owners, but the good news is that with proper treatment and regular vet check-ups your dog can continue to live a good quality life for years to come.