Cushing's Disease in Dogs

Overview:

Hyperadrenocorticism, (also known as Cushing's syndrome or Cushing's Disease) is an endocrine disorder caused by excessive production of cortisol by the adrenal gland (the adrenal cortex, which is the outer part of the gland), or administered medically. 

Middle aged & older dogs are most often affected. 

What are the causes of Hyperadrenocorticism in dogs?

There are three causes of Hyperadrenocorticism in dogs: 

• Pituitary tumour (Cushing's Syndrome) - Micro tumours in the pituitary gland can lead to it producing excessive amounts of adrenocorticotrophic hormone (ACTH). ACTH stimulates the adrenal glands to produce too much cortisol. This is known as pituitary dependent hyperadrenocorticism. Approximately 85% of cases of Cushing's Syndrome are caused by these tumours.

• Adrenal tumours (Cushing's Disease) -  In adrenal hyperadrenocorticism, one or both of the adrenal glands ignore the ACTH signal & begin to produce excessive amounts of corticosteroids. This is usually the result of a benign or cancerous tumour. This is known as adrenal dependent hyperadrenocorticism. 

• Iatrogenic Cushing's (Veterinary induced) - Iatrogenic Cushings is the result of too much corticosteroids (especially cortisol) is given either orally, topically or by injection. 

What are the symptoms of cushing's disease in dogs?

Symptoms of cushing's disease include;

• Increased thirst (polydipsia) 

• Increased urination (polyuria)

• Increased appetite (polyphagia)

• Enlarged abdomen

• Muscle wasting

• Hair loss (bilateral symmetrical hair loss)

• Thin skin which is easily damaged (fragile skin syndrome)

• Muscle weakness & wasting

• Lethargy/decreased activity

• Testicular atrophy

• Enlarged liver

How is it diagnosed?

Hyperadrenocorticism may be tentatively diagnosed if your dog has a history of long term corticosteroid use, and upon clinical signs & physical examination of the dog.  

Diagnostic testing may involve a routine tests such as

• Complete blood count: This may show an increase in levels of red blood cells

• Biochemical profile may reveal low calcium levels, elevated cholesterol, elevated glucose, possible elevated alkaline phosphatase & liver enzymes.

• Urinalysis

• ACTH stimulation test: This test measures the ability of the adrenal glands to respond to a hormone known as adrenocorticotrophic hormone (ACTH) which is made in the pituitary gland, travelling through the bloodstream to the adrenal glands where it stimulates the secretion of other hormones such as hydrocortisone from the cortex. The ACTH stimulation test measures levels of cortisol in the blood before & after an injection of synthetic ACTH.

• Low dose dexamethasone suppression test (also known as ACTH suppression test): This test can help distinguish between adrenal dependent hyperadrenocorticism (ADH) & pituitary dependent hyperadrenocorticism (PDH). It measures the response of the adrenal glands to ACTH. Dexamethasone is a synthetic steroid (similar to cortisol)  which suppresses ACTH. Dexamethasone is administered  & blood cortisol levels are measured. Cortisol levels should decrease in response to the administration of dexamethasone.

• Urine Cortisol:Creatinine Ratio (UC:Cr): This tests levels of cortisol in the urine &  is measured against levels of creatinine. If the level is normal, hyperadrenocorticism can be ruled out.

• Abdominal x-rays can be useful to check for enlarged adrenal glands, calcifidogion of the adrenal glands or other organs & an enlarged liver (hepatomegaly).

• Ultrasound: This can enable the veterinarian to measure the adrenal glands.

In the case of spontaneous hyperadrenocorticism, your veterinarian will need to establish which gland is causing the disease. 

More detailed information on diagnostic tests for Hyperadrenocorticism can be found on this page.

How is it treated?

Surgical removal of the adrenal gland/s (adrenalectomy). If the disease is caused by an adrenal tumour in one gland, then only the affected gland will be removed. If the disease is caused by a pituitary tumour then both the adrenal glands will be removed. Adrenalectomy is a risky & difficult operation, and once the adrenal glands are removed your dog will have to have have replacement therapy with glucocoricoids & mineralocorticoids throughout their lives. 

Dogs with pituitary-dependant hyperadrenocorticism can be managed medically by oral administration of certain drugs such as mitotane to destroy the abnormal pituitary tissue.

If the disease is caused by the use of corticosteroids then the medication will be gradually withdrawn. This needs to be done slowly & carefully to give the adrenal glands the chance to begin functioning properly. 

Your veterinarian will be able to best advise you on the latest treatment options.

Please note:

The medical articles on this site have not been written by a veterinarian & should not be considered a replacement for a veterinarian visit. The articles are provided for informative purposes only.

Always seek immediate veterinary advice for any problems (health or behavioral) in your pets. 

While great care has been made in the creation of these articles, we cannot guarantee the accuracy or omissions on these pages. If in any doubt whatsoever, seek professional medical advice.