Cushings Syndrome

What is Cushings syndrome?

Cushings syndrome or hyperadrenocorticism is a complicated condition caused by high circulating levels of cortisol (commonly known as cortisone) in the blood stream.

Cortisol, cortisone or corticosteroid are all names used to describe the principal hormone secreted by the outer part or cortex of the adrenal gland, hence the term hyperadrenocorticism, indicatesover production from the adrenal cortex.

High levels of circulating cortisol can have multiple effects on the body, affecting many important organs and systems. These can include kidneys, bladder, skin, as well as the reproductive, nervous and muscular skeletal systems.

Today Cushings syndrome is recognised as one of the most common hormonal diseases of the dog.

What causes it?

Spontaneous over-production of cortisol by the adrenal cortex can be due to two main causes.

1.  Adrenal dependent hyperadrenocorticism (ADH) 

Cortisol excess with this type is usually caused by a tumour of the adrenal gland. ADH occurs more frequently in larger breeds of dogs and is most commonly seen in dogs of 9 years of age or older. ADH only accounts for 10-15% of all dogs with Cushings syndrome. 

2.  Pituitary dependent hyperadrenocorticism (PDH).

Here the cause is over-production of a hormone which controls the secretion of cortisol by the adrenal glands. This is adrenocorticotrophic hormone, (ACTH). Again, this over-production is usually caused by a tumour or a nest of overactive cells, in this case in the pituitary gland. Altogether approximately 85% of all cases of Cushings syndrome seen in dogs is due to PDH. It can occurin young dogs however typically they are middle-aged to older.

Are any particular breeds more commonly affected?

Any dogs, including mixed breeds, can be affected.  Poodles, Dachshunds, small Terriers, Boxers and Beagles have been reported to be at higher risk.

Does sex play a part?

Both dogs and bitches, whether neutered or entire, are equally at risk with PDH but adrenal tumours causing ADH are possibly more common in females.

What are the clinical signs?

The most common signs areusually increases in thirst and urination. Appetite also increases markedly. Other common signs include a pendulous abdomen, hair loss (often bilateral), lack of energy, muscle wastage and obesity. In addition to these there are other signs that can occur, e.g. panting, pigmentation of areas of the body that have lost hair, and lack of sex drive. Some dogs are presented solely because of hair loss and a paper thin skin, often attributed to old age by their owners.

Are there any other causes?

PDH and ADH are the two known causes of spontaneous Cushings syndrome. However iatrogenic Cushings can occur. With this, the excess of cortisone has resulted from excessive administration of the drug. This may occur as a result of medication for other conditions, e.g. chronic skin irritation over a long period. Usually the dose prescribed is well within the normal range. Unfortunately over time the effects of the corticosteroid on the body have built up and become detrimental.

Administration need not be by mouth or injection. Cortisone containing ointments over a long period can result in iatrogenic Cushings syndrome. This is due to absorption through the skin and licking by the dog of the ointment applied.

How is it diagnosed?

Cushings syndrome can be accurately diagnosed with a series of blood tests one of which is the ACTH stimulation test or the low dose dexamethasone suppression test (LDDS). Other tests will also be needed to distinguish between ADH and PDH. Some of the tests are expensive but are essential for accurate diagnosis and successful treatment.

"Cushings syndrome can be accurately diagnosed with a series of blood tests one of which is the ACTH stimulation test or the low dose dexamethasone suppression test (LDDS). Other tests will also be needed to distinguish between ADH and PDH."

How successful is treatment?

Depending on the cause, the disease can be successfully treated and controlled, if not cured.  

What are the treatment options?

1.  Iatrogenic Cushings syndrome. Administration of cortisone for whatever medical reason has to be discontinued or at least drastically reduced. Unfortunately in some cases, e.g. intractable allergic conditions, this can result in recurrence of the original problem.

2.  ADH. Some adrenal tumours are amenable to surgery. Although this is a complicated procedure and not without risk, if successful and the tumour is benign, there is a good chance that the dog will return to normal. If surgery is not an option then medical therapy can be used as per PDH.

3.  PDH. Registered medication is available in Australia for the treatment of this form of Cushings syndrome but treatment with this drug may have to be continued for life and regular monitoring (approximately every three months) will be necessary. Therefore treatment can be costly. Differing options for treatment can be discussed with you by your veterinarian.