The adrenal glands are part of the endocrine system and are located at the top of each kidney. The endocrine system is made up of a series of ductless glands that produce and secrete the hormones responsible for regulating different functions in the body. The adrenal gland produces several hormones, one of which is the hormone Cortisol. Cortisol is responsible for helping the body respond to stress, as well as many other functions.
The condition associated with the body producing too much cortisol is medically referred to as hyperadrenocorticism, or Cushing’s disease. Cushing’s disease is one of the most common endocrine disorders that affects dogs. It generally affects middle-aged to older animals.
Between 80-85% of Cushing’s is caused by a tumour in the pituitary gland, which is located near the bottom of the brain. The pituitary gland is referred to as the “master” gland as it regulates the functions of other glands. A tumour in the pituitary gland is usually benign (it doesn’t spread through the body) and can cause it to send messages to the adrenal gland to produce higher levels of Cortisol. This is known as Pituitary dependent Cushing’s. A smaller minority of naturally occurring Cushing’s, is caused by a tumour within the adrenal glands. If the tumour is within the adrenal glands, there is a 50/50 chance that it is malignant. In some cases, Cushing’s-like symptoms can be caused by high dose or long-term administration of steroid medications.
(Note: a lot of these symptoms can be associated with other diseases.)
To determine whether a dog has Cushing’s disease, your veterinarian will look at the results of several different diagnostic tests.
The first step is to run some basic blood tests to see if the blood chemistry shows any changes. Your Veterinarian may also test your dog’s urine. This is known as urinalysis. (this looks at the concentration of your dog’s urine)
If the results are suggestive of Cushing’s, your Veterinarian may run additional tests. Unfortunately, there may need to be more than one test, because there isn’t a single definitive test for Cushing’s in all cases.
The most common test used to diagnose Cushing’s disease in dogs is the low-dose dexamethasone suppression test (LDDST). Your Veterinarian will take a blood sample to measure the baseline cortisol level, and then a small amount of a drug called dexamethasone is administered by injection. Blood cortisol levels are then measured four and eight hours after the dexamethasone is given. In a normal dog, the dexamethasone injection will inhibit the secretion of the hormone that stimulates cortisol secretion, and this leads to a decrease in circulating cortisol levels. In a dog with Cushing’s disease, the cortisol is not supressed.
It may also be necessary to run an ACTH stimulation test and an abdominal ultrasound.
If Cushing’s develops due to corticosteroid medications, your Vet may suggest slowly weaning your dog off these medications over a period of time under supervision. It must be done slowly, or it can lead to a life-threatening crisis, known as an Addisonian crisis.
If your dog has mild symptoms associated with pituitary-dependent Cushing’s disease, your Veterinarian may hold off on any form of treatment and may instead choose to closely monitor your dog to determine when treatment would be beneficial.
Signs that the condition may need medical treatment, are:
Your Vet may decide that your dog may need medication to treat pituitary-dependent Cushing’s. The medication can have serious side effects, and may interact with other medications, so it is important to discuss any medications or supplements you may be giving your dog.
If the Cushing’s is a result of an adrenal tumour, your Vet may recommend chest radiographs and possible CT or MRI scans to look for any possible metastatic spread of the disease. If no metastases are seen, the dog is often given a medication for a few months to shrink the tumour, and then surgery may be recommended to remove the tumour.
Typical side effects of the medication include:
If you notice any of these side effects, you should contact your Vet immediately. Because of the risks associated your Vet may monitor the Cortisol levels and hold off medication.
The information in this website and fact sheets is general and should not be used as a substitute for seeking Veterinary medical advice or diagnosis from your Veterinarian