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Canine Cushing's Disease (Hyperadrenocorticism)

Cushing’s disease was first described in humans by Dr Harvey Cushing in 1932. It would have been discovered in dogs soon afterwards. In dogs, the term Canine Cushing’s Syndrome (CCS) basically describes all the symptoms we see when there is an excess of the body’s natural circulating cortisol. It is also called Hyperadrenocorticism.

Cortisol is required by most organs of the body for normal function. In normal pets the cortisol levels are carefully controlled by coordination of the pituitary gland and the adrenal glands. The pituitary gland makes a hormone (ACTH) to stimulate the adrenal glands to make cortisol. When the level of cortisol in the blood is adequate, the cortisol itself inhibits the pituitary gland from making any more ACTH. Therefore, cortisol production by the adrenal glands will stop. This is called a negative feed back system.

Two faults can occur with this system which may lead to CCS:
  1. A tumour in the pituitary gland will produce too much ACTH leading to excess cortisol production. The normal negative feedback systems fails. The adrenal glands grow in size due to the demand placed on them by the high levels of ACTH. Blood cortisol levels become too high and the body is unable to regulate them. This is known as Pituitary-Dependent Hyperadrenocorticsim and is the most common form in dogs
  2. A tumour can occur in the adrenal glands which produces cortisol. This tumour produces cortisol continuously regardless of the ACTH levels. Once again blood levels of cortisol become too high and unregulated. This is known as Adrenal Hyperadrenocorticism

Clinical Signs of Canine Cushing's

The chronic high levels of cortisol in the body lead to a variety of clinical signs:
  • Polydipsia (excess drinking)
  • Polyuria (excess urinating)
  • Polyphagia (excess eating)
  • Abdominal enlargement
  • Skin problems/Hair loss
  • Panting
  • General muscle weakness

Diagnosis

If both the animal’s history and a thorough examination suggest a patient may have CCS, then urine and blood tests are the next step. If these also indicate CCS is a likely diagnosis we will perform one or two Dexamethasone Suppression Tests. While not 100% accurate these tests are the only way to diagnose the condition definitely.
This test involves giving the patient an intravenous dose of cortisone and monitoring the response of the natural cortisol levels in the blood.

Treatment

Once a diagnosis of CCS has been made the aim of treatment is to reduce the circulating cortisol levels to the normal range. In most cases treatment is by medical means. There are some cases where surgery is possible. your Vet will advise on the best course of action.