Cushing’s Disease in Dogs
Hypercortisolism or hyperadrenocorticism, also commonly known as Cushing’s disease, occurs when the dog’s body produces too much of the hormone, cortisol. At the right amount, cortisol is responsible for fighting infection, control weight and blood sugar levels, as well as helps respond to stress. Too much of this hormone, however, could cause a wide range of health problems for the dog.
Types of Cushing’s Disease in Dogs
The adrenal glands are a pair of ductless glands that are located next to each kidney and responsible for producing and secreting cortisol. Different factors could result in elevated levels of cortisol in the blood. And the different types of Cushing’s disease in dogs are categorized depending on the primary cause of the overproduction of cortisol.
Pituitary Dependent Cushing’s Syndrome
Approximately 80%-85% of dogs have this type of Cushing’s disease and this is caused by a tumor in the pituitary gland. The pituitary gland is located in the brain and is often referred to as the “master gland” since it is responsible for controlling the functions of other glands, including the adrenal glands.
The tumor, which can be benign or malignant, will cause the pituitary gland to produce too much adrenocorticotropic hormone (ACTH). Elevated levels of ACTH will lead to the overstimulation of the adrenal glands resulting in the overproduction of cortisol. Depending on the size of the tumor, the dog may also suffer from neurological symptoms aside from the common clinical signs of Cushing’s disease.
Adrenal Tumor Hypercortisolism
Another possible cause of elevated cortisol levels is tumor growth in either adrenal glands. This accounts for roughly 15%-20% of Cushing’s disease in dogs. The tumor can be benign (adenoma) or malignant.
Iatrogenic Cushing’s Disease
This is the rarest type of Cushing’s disease in dogs and brought about by excessive use of the steroids. Dogs that have been using injectable or oral steroids as a treatment for some other disease may soon develop symptoms of Cushing’s disease.
Signs and Symptoms
Regardless of the type of Cushing’s disease, the signs and symptoms are generally the same. Due to elevated levels of cortisol, the hormone that stimulates appetite, the dog will experience increased appetite. Aside from that, it will also exhibit other signs like increased water consumption, frequent urination, pot-bellied appearance, lethargy, and unhealthy hair coat.
Furthermore, dogs who are suffering from Cushing’s disease are at risk for developing skin or bladder infection, skin mineralization, and hyperpigmentation.
During the visit to the vet, the pet owner will be asked about the symptoms and their onset. Routine blood tests and urinalysis will also be performed. If Cushing’s disease is suspected, the vet may request for additional hormone screening tests that confirm Cushing’s disease. The most common of these are:
ACTH stimulation test
This test assesses how well the adrenal glands respond to ACTH. To perform this, the vet will take a blood sample before an ACTH shot is administered. Another blood sample is taken to check the variation of cortisol levels before and after the shot was given. A positive result of this test will confirm that the dog is suffering from Cushing’s disease but this does not determine which type.
Low dose dexamethasone suppression test
This test mimics a naturally occurring feedback loop involving the pituitary and adrenal glands to confirm Cushing’s disease and check which type is present. In a normal system, the pituitary gland secretes ACTH to stimulate the adrenal glands to produce and release cortisol. When the blood cortisol level increases, the pituitary gland will decrease ACTH secretion in response, which leads to a lower blood cortisol level.
During this screening test, a blood sample is taken from the dog prior to administering a shot of synthetic cortisol (dexamethasone). After dexamethasone is injected, a blood sample is taken after 4 hours and another is taken after 8 hours. If the production of ACTH and cortisol is mildly suppressed in the 4- and 8-hour levels, this is indicative of Cushing’s disease caused by a tumor of the pituitary gland. If there’s no reduction of ACTH or cortisol level in the blood, then it is of adrenal origin.
Once Cushing’s disease is diagnosed, the vet may also request further imaging tests like ultrasound, CT scan, or MRI to get a visual of the tumor and its size as well as check it for evidence of malignancy.
The treatment approaches to this disease are either medical or surgical. Also, the treatment plan is largely dependent on which type of Cushing’s disease the dog is suffering from.
Pituitary Dependent Cushing’s Disease
Ideally, surgical removal of the tumor will treat the disease. But since this is not widely available and some dogs are not healthy enough to go through surgery, taking oral medications that either suppress cortisol production or kill cortisol-producing cells is the more common treatment plan. Some of the widely-used drugs are mitotane and trilostane.
Adrenal Tumor Hypercortisolism
To treat adrenal-related Cushing’s disease, surgical removal of the tumor is the best option. However, prior to surgery, the dog may have to take some medication first. After the surgery, the dog can regain its health without any problem as long as the tumor is benign although it may have to undergo a cortisol replacement therapy for a few weeks or months.
Iatrogenic Cushing’s disease
Since this is caused by excessive use of steroids, the medication may have to be discontinued gradually. The downside is that the disease that was treated with the steroid might recur.
Cost to Treat
Depending on your dog’s health, and the treatment option you may choose, there may be many risks involved when treating Cushing’s disease. Since many of the treatment options for Cushing’s disease involve certain chemicals to re-establish a balanced level of cortisol, it is possible for your dog to develop a condition that occurs when cortisol levels are too low. This is called Addison’s disease, and is the opposite of Cushing’s disease.
Depending on the cause and severity of the disease, age and health of your dog there are various options available including medications to regulate cortisol levels, radiation therapy or surgery.
Cost to Treat: $500 to $2,000
Generally, the outlook for dogs with this disease is positive since this is very treatable. Dogs that are diagnosed with a malignant adrenal tumor, however, have different prognoses. In this case, the outlook is dependent on whether cancer has spread to other parts of the body prior to the removal of the tumor. There are instances wherein the tumor was removed before it has a chance to metastasize and the dog won’t have further problems with Cushing’s disease. But the prognosis is guarded to poor if cancer has spread already.
A good deal of aftercare is focused on making sure the pet is taking all the necessary medication as prescribed. Also, pet owners must maintain close communication with the veterinarian and his team so they can monitor how the dog responds to its medications.