Cushing’s syndrome (hyperadrenocorticism) is common in dogs and occurs due to an overproduction of cortisol from the adrenal glands. There are three types of Cushing’s disease.
Posted: 10 October 2019
The three types are;
The condition affects mainly middle-aged and older dogs, with the signs being subtle and easily missed at first. It’s worth considering a diagnosis of Cushing’s if the animal shows some or all of the following;
Cushing’s should always be included on the list of differentials in any dog with polyuria and polydipsia, dilute urine whilst showing normal haematology and serum chemistry profile results.
There are several tests available, but the two tests most frequently used to confirm a diagnosis of Cushing’s are the low-dose dexamethasone suppression test and the ACTH stimulation test.
In this test, a low dose of dexamethasone is injected, and the cortisol response measured. In the normal dog, the dexamethasone will completely suppress the production of cortisol, whilst in dogs with Cushing’s, the cortisol levels stay raised. Three blood samples are taken, one prior to injecting the dexamethasone, and two post injection, around 4 and 8 hours later.
This test checks the response of the adrenal glands to stimulation by the adreno-corticotrophic hormone (ACTH). Blood samples are taken to measure cortisol before and 1 hour after injecting a synthetic version of ACTH. Cortisol levels after injection will increase dramatically above normal in most dogs with Cushing’s. Levels greater than 550 - 600 nmol/l will certainly indicate a problem.
In some instances, it may be recommended to perform both the above cortisol response tests, as neither of them are perfect. To help assess the results, it’s also important to consider the results in combination with any other supporting preliminary blood and urine tests. Some of the evidence may include;
This is a common finding in all mammals as a response to the exposure to prolonged periods of stress hormones (cortisol). In dogs with hyperadrenocorticism, look for;
In around 1/3 of dogs, the elevated cortisol has effects on hepatic gluconeogenesis and peripheral insulin, resulting in an overall increase in blood glucose. A hypercortisolism induced hyperinsulinemia may eventually develop as the pancreas continues to secrete insulin in an attempt to maintain normal glucose levels. A small percentage of dogs will develop diabetes.
Cortisol can increase lipolysis in fatty tissue, generating both free fatty acids and glycerol, which will in turn lead to an increase in blood cholesterol. Almost all dogs with Cushing’s will show signs of hypercholesterolaemia.
The majority of dogs with Cushing’s will have clinical evidence of polyuria and polydipsia. In most dogs, urine specific gravity is less than 1.030, though it can often be much lower, with a urine specific gravity between 1.007-1.015.
There are two main treatment options for Cushing’s. The most popular approach is using medication to reduce the amount of cortisol produced by the adrenal glands. In the UK, the drug of choice is Vetoryl. Surgery to remove an adrenal or pituitary tumour may also be considered, but this is not without risk and considerably more difficult to achieve.
Vetoryl – this is the only licensed treatment for use in dogs. Find out more here >
For much more client information on canine hyperadrenocorticism, see this excellent website, www.canine-cushings.co.uk. It contains a wealth of information and resources designed to support dog owners whose pets have been prescribed Vetoryl, and to allow them to understand the condition and monitor their progress.
Diets appropriate for dogs suffering from Cushing’s are aimed at managing any secondary and underlying disease processes. Avoid feeding treats that are fatty or high in sugar. Commercial diets formulated for adult maintenance are usually ideal. They should be able to compensate for any muscle waste associated with the disease. Look for diets which are;
The main effects of hyperadrenocorticism are seen by the owner in terms of reduced quality of life. However, there are a number of more serious conditions which can occur if the left untreated. These include: