Understanding Canine Cushing’s

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

Understanding Canine Cushing’s

Share:

The three types are;

  • Pituitary dependent – the adrenal glands overproduce cortisol as a result of overstimulation from pituitary hyperplasia or a pituitary tumour. This accounts for around 85% of all cases.
  • Adrenal dependent – the adrenal gland overproduces cortisol because of an adrenal tumour.
  • Iatrogenic - this form of Cushing’s syndrome can be induced if the animal is given an excessive dose of glucocorticoids.

Common clinical signs

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;

  • Polyuria
  • Polydipsia
  • Polyphagia
  • Panting
  • Alopecia
  • Thin skin
  • Pot-bellied appearance

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. 

Making a diagnosis

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.

1. The low-dose dexamethasone suppression 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.

2. The ACTH stimulation test

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.

Look for supporting evidence

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;

A. Stress haemogram

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;

  • Lymphopaenia – this occurs as a result of a redistribution of lymphocytes within the circulation
  • Eosinopaenia – elevated cortisol levels result in eosinophils being sequestrated in bone marrow and other tissues
  • Neutrophilia – this occurs as mature neutrophils are released from the bone marrow and pooled neutrophils are redistributed
  • Monocytosis – this is not always seen, but when it is, it’s as a result of a shift of marginated monocytes from the periphery into circulation
  • Thrombocytosis - 75% to 80% of dogs show an increase in platelet numbers

B. Liver enzymes elevated

  • Serum alkaline phosphatase (ALP) – this is the most common abnormality found with hyperadrenocorticism, with the increases varying from mild to severe. 
  • Alanine aminotransferase (ALT) – this happens as a result of hepatocytes swelling, hepatocellular necrosis, accumulation of glycogen and variations and disturbances in hepatic blood flow. The increases in ALT are generally mild.

C. Hyperglycaemia

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.

D. Hypercholesterolaemia

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.

E. Low urine specific gravity

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.

How is Hyperadrenocorticism treated?

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.

Are there any special dietary requirements?

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;

  • Low in Fat – this is to help manage the hypercholesterolaemia.
  • Low in Sodium - to help maintain normal blood pressure.
  • Digestible – specifically containing digestible proteins such as egg whites, chicken and fish

At Burgess Pet Care we produce a variety of digestible adult diets which would be suitable, such as Supadog Finest Adult Light Chicken. Find out more about our range of canine diets here.

What happens if Cushing’s is left untreated?

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:

  • Diabetes mellitus
  • High blood pressure
  • Pancreatitis
  • Urinary tract infections
  • Pulmonary thromboembolism

Share: