Cushing’s Syndrome in Dogs: Spotting and Treating This Complicated Disease
Your dog has been looking bloated and his once shiny coat is faded and falling out. Plus, he’s constantly panting, drinking water, and starting to have accidents all over your house. Your veterinarian thinks he might have Cushing’s syndrome. This condition will require surgery or lifelong medication, but the good news is your dog can get back to his normal self!
What Is Cushing’s Syndrome in Dogs?
Cushing’s syndrome, also known as hyperadrenocorticism, is when your dog is producing too much cortisol in his body. Cortisol is a steroid hormone that helps your dog’s body respond to stress, control weight, fight infections, and regulate blood-glucose levels. While some cortisol is necessary for a normal, healthy life, too much or too little of it can wreak havoc.
Cortisol production is controlled by two kinds of glands. The pituitary gland, located at the base of the brain, produces adrenocorticotropic hormone (ACTH) in response to stress. The ACTH then stimulates the adrenal glands, located next to each of your dog’s kidneys, to produce cortisol. As cortisol levels in the blood rise, the pituitary gland senses that and stops producing ACTH to prevent the production of too much cortisol. This is called a negative feedback loop. Cushing’s syndrome occurs when a malfunction in this loop causes too much cortisol to be produced and circulated in the body.
Why is hyperadrenocorticism called Cushing’s syndrome? This is a nod to Dr. Harvey Cushing, an American neurosurgeon and the first person to describe this condition.
Are Cushing’s Disease and Cushing’s Syndrome the Same Thing?
Yes and no. Technically, Cushing’s syndrome is the overarching term for hyperadrenocorticism, when there is excess cortisol production. Cushing’s disease is a specific type of hyperadrenocorticism caused by a tumor in the pituitary gland resulting in overproduction of ACTH. It's called pituitary-dependent hyperadrenocorticism (PDH). This is the most common cause of Cushing’s syndrome in dogs, so the term Cushing’s disease is frequently used interchangeably with Cushing’s syndrome. There are actually three primary types of Cushing’s syndrome.
This is Cushing’s disease: when a tumor forms in the pituitary gland and causes it to overproduce ACTH, resulting in the overproduction of cortisol. The tumor may be benign or malignant. Most pituitary tumors are small, but large ones may cause neurological symptoms as they grow. According to the American College of Veterinary Internal Medicine (ACVIM), PDH is responsible for 80–85 percent of cases of Cushing’s syndrome in dogs.
The remaining 15–20 percent of dogs with Cushing’s syndrome have adrenal-dependent hyperadrenocorticism (ADH). These dogs have a tumor on one or both of the adrenal glands, causing an overproduction of cortisol even though the pituitary gland is functioning normally. These tumors can also be benign or malignant.
A third, less common cause of Cushing’s syndrome in dogs is iatrogenic Cushing’s, caused by long-term or high-dose steroid use to treat another health condition.
Signs and Symptoms of Canine Cushing’s Syndrome
The common symptoms of Cushing’s syndrome in dogs include:
- Increased thirst
- Increased urination
- Increased appetite
- Hair loss and thinning of hair, especially on the back and abdomen
- Pot-bellied appearance
- Loss of muscle mass
- Thin, delicate skin
- Decreased activity
- Recurring skin issues
- Dark spots of pigment on the skin
- Recurring urinary tract infections
- High blood pressure
“It is a chronic and progressive disease, meaning that the condition begins slowly with mild or subtle symptoms that commonly become more and more obvious with time,” the ACVIM says. Middle-aged and senior dogs are the most commonly affected.
Dog Breeds Prone to Cushing’s Disease
Cushing’s syndrome can affect any dog breed or mix, but it is seen in some breeds more commonly than others. These include:
Diagnosing Cushing’s Syndrome in Dogs
As with many diseases, the symptoms of Cushing’s syndrome in dogs overlap with the symptoms of many other conditions. The symptoms are also the same for all three types of Cushing’s syndrome.
The first step to making a diagnosis of Cushing’s syndrome is for you to notice changes in your dog’s behavior and/or appearance and make an appointment with your veterinarian. Make a list of any abnormalities and when you first noticed them to provide your vet with as much information as possible.
To accurately diagnose any of the three types of Cushing's syndrome, your vet will start off with a physical exam and a series of screening tests.
ACTH Stimulation Test
This is a blood test that can confirm if your dog has Cushing’s syndrome by evaluating his response to adrenocorticotropic hormone (ACTH), which is the hormone that regulates cortisol levels.
Urine Cortisol: Creatinine Ratio (UCCR)
This test requires a urine sample from your dog. Creatinine is produced at a constant rate, while cortisol levels in the urine increase if the dog has Cushing’s syndrome and is producing excess cortisol.
Low-Dose Dexamethasone Suppression Test (LDDS)
This blood test evaluates your dog’s response to increased cortisol levels. Your vet will draw a blood sample and then give an injection of dexamethasone (synthetic cortisol). Dogs with PDH typically still have some response to elevated cortisol levels and the pituitary gland will slow down ACTH production to control cortisol levels (but not as much as in a dog with a totally normal pituitary gland). Dogs with ADH won’t show any decrease in cortisol levels because the diseased adrenal glands have gone rogue.
High-Dose Dexamethasone Suppression Test (HDDS)
The procedure for this test is the same as the LDDS, but a higher dose of the dexamethasone is given. The higher dose can trigger the negative feedback loop in PDH, causing a depression of cortisol levels. If the test results still show no depression of cortisol, it can confirm that the dog has ADH.
Endogenous ACTH Levels
This blood test checks the levels of ACTH in the blood. If the dog has a pituitary tumor, he should have abnormally high ACTH levels. Unfortunately the ranges for normal ACTH levels, ADH, and PDH can overlap, so the results of this test do not always give a clear-cut answer.
Abdominal Ultrasound and Other Imaging
An ultrasound can be done to look for tumors on the adrenal glands. In some cases, an MRI or CT scan may be recommended to look for pituitary gland tumors or to confirm the presence of an adrenal gland tumor.
While this series of tests typically confirms a Cushing’s syndrome diagnosis, they do not determine the cause of the disease.
Expect that getting to the final diagnosis of pituitary-dependent or adrenal-dependent hyperadrenocorticism will take at least two rounds of testing, possibly three. It can be frustrating to get inconclusive results, but rest assured that each test allows your veterinarian to narrow down your dog’s diagnosis and make sure that you are making the right treatment choices.
Treatment for Cushing’s Syndrome in Dogs
Treatment for this disease depends on the type of Cushing’s syndrome that your dog has. The most common treatment options across the spectrum include:
- Radiation therapy
- Gradually stopping corticosteroid use (if applicable)
Pituitary-dependent Cushing’s can be cured by surgically removing the tumor from the pituitary gland. Brain surgery is not to be undertaken lightly, however, and will require a visit to a specialist, along with the travel and cost associated with that.
More commonly, PDH is treated with medications to either block cortisol production or kill the cells that produce it. No medications cure Cushing’s, so your dog will be on them for the rest of his life. He may need dosage changes, so it is important to follow your veterinarian’s protocols for recheck blood work.
Adrenal-dependent Cushing’s can often be treated by surgically removing the tumor from the adrenal gland(s). If the tumor is benign, removal can provide a full cure. If the tumor is cancerous, the prognosis will depend if the cancer has already spread or not. Malignant tumors are also more likely to grow back.
Radiation therapy is also an option for treating the tumors that cause Cushing’s syndrome, and it can be done in conjunction with other therapies if warranted.
For iatrogenic Cushing’s, in which the symptoms were caused by corticosteroid therapy to treat a different condition, weaning off the steroids will usually resolve the Cushing’s. Never stop corticosteroids abruptly, as this can do further damage to your dog’s metabolism. If the adrenal glands have been harmed, it may be necessary to supplement some of the hormones that they produce to keep your dog’s body working properly. This may only be temporary or might be needed long term. It is also important to note that stopping the steroid therapy will likely cause your dog’s original health condition to return, so a new treatment plan for that may be needed.
Life Expectancy with Canine Cushing’s Syndrome
The American College of Veterinary Internal Medicine says that most dogs treated for Cushing’s respond extremely well. Dogs can live healthy, normal lives once they have been treated with surgery or are on a stable medication schedule.
It is important to follow medication instructions closely to ensure your dog is getting his meds at the right times. He will also need to go to the vet regularly for blood work to make sure the treatment is still effective at the current dose. The ACTH stimulation test is frequently used to monitor response to treatment, and may be done monthly at first while your vet is determining the ideal medication dosage and then dropped back to once or twice a year when your dog is stable.
The presence of other health conditions can affect the prognosis for a dog with Cushing’s syndrome. Diabetes mellitus is one of the most common diseases for dogs to have in addition to Cushing’s, but senior dogs can fall victim to a variety of conditions. Additional illnesses can have an effect on your dog’s response to treatment. Discuss all of your dog’s medications with your vet to ensure that there won’t be any adverse interactions.
If your dog has just been diagnosed with Cushing’s disease, expect that it may take a few months to get him completely stable on a medication schedule that works for him and controls his symptoms. Be patient during this process and stay in contact with your veterinarian. But if after several months and dosage changes your dog is still not stabilized and doing well, it may be time to consider his quality of life. Many dogs with Cushing’s syndrome do well once they have been diagnosed with the disease and are started on a treatment plan, and although it is an extremely difficult decision, euthanasia is an option you can discuss with your vet if your dog is suffering or has a poor quality of life.