Question from Carol Fogerty

Hi, my vet says my poodle cross Pom, may have Cushing’s disease what is this please?

Answer from Shanika Winters MRCVS, Online Vet

Hi Carol and thank you for asking about Cushing’s disease (HAC hyperadrenocorticism) which is a condition where the body makes too much of the steroid cortisol which can result in a variety of symptoms.  HAC is most common in middle-aged to older dogs but does also affect cats, horses, hamsters and ferrets.

There are three different types of HAC:

Pituitary dependant HAC (PDHAC) is the most common type and this is when a tumour of  the pituitary gland in the brain is making too much of a hormone called adrenocorticotrophic hormone (ACTH)  this causes the adrenal glands to make too much cortisol.

Adrenal dependant HAC (ADHAC) is less common, this is when a tumour of the adrenal glands causes too much cortisol to be produced.

Iatrogenic HAC (IHAC) is when very high doses of steroid given as medication lead to symptoms of HAC.

What are the signs of HAC?

If your pet is showing some of the following signs then your vet may suspect HAC:

Increased drinking (PD polydypsia), increased urinating (PU polyuria), increased appetite (PP polyphagia), a large rounded low slung abdomen ( tummy), muscle weakness, hair loss on both sides (bilateral symmetrical alopecia), hard areas under the skin due to deposits of the mineral calcium (calcinosis cutis) and dark spots on the skin due to blocked keratin (hair protein) filled hair follicles  (comedones).

How do we test for HAC?

There are several blood tests, urine tests and diagnostic imaging tests that can be done to try and make a diagnosis of HAC:

  1. Routine blood tests in cases of HAC may show up increased levels of liver enzymes, increased cholesterol, increased blood glucose (blood sugar) and also changes to the white blood cell numbers.
  2. Routine urine tests may show an increase in glucose, white blood cells and protein.

More specific tests for HAC include:

  1. Urine creatinine: cortisol ratio, here a urine sample collected from your pet is sent to a laboratory for analysis, abnormal results are found in cases of HAC but can also suggest diabetes, liver disease or womb infection (pyometra). ACTH stimulation test, this is a set of blood tests in which a blood sample is taken from your pet, an injection of artificial ACTH is given into a vein (blood vessel) and 1-2 hours later another blood sample is collected. The laboratory results are abnormal in approximately 80% of dogs with HAC, this test is also often used to monitor dogs on treatment for HAC.
  2. Plasma cortisol level, this is a blood test which directly measure the level of cortisol in the blood , the blood sample has to be treated very carefully and sent to the lab quickly so as to get an accurate result.
  3. Ultrasound scan of the abdomen can be used to check the size of the adrenal glands (found next to the kidneys), look for a tumour and assess the other abdominal organs. IN PDHAC the adrenal glands are usually normal size or slightly enlarged with ADHAC the adrenal glands are usually different sizes, the large irregular gland being the one with the tumour.
  4. Low and High dose dexamethasone suppression test (LDDST & HDDST) are blood tests where the effect of artificial steroid on the adrenal glands is measured, the results can sometimes help tell apart PDHAC form ADHAC.
  5. Magnetic resonance imaging (MRI) scans and computed tomography (CT) scans can be performed at referral centres to help in the diagnosis of HAC and also tell which type it is.

How is HAC treated?

Trilostane is a tablet with blocks a step in the production of cortisol in your pet’s adrenal glands therefore decreasing the amount of cortisol in your pet’s body.

Mitotane is another tablet which works by destroying the parts of the adrenal glands that produce cortisol.

Surgery to remove the actual tumours can be performed usually at referral centres.

Trilostane and mitotane are the most commonly used treatments for HAC, they are effective on both PDHAC and ADHAC and your pet should have regular blood tests to monitor that the dose given is correct for your pet. Too much medication for HAC can lead to symptoms of Addison’s disease (Hypoadrenocorticism) where there is not enough cortisol which includes dehydration, depression, diarrhoea and lethargy (weakness).

I hope that my answer has given you some useful information about HAC, the exact test done on your pet will need to be discussed with your vet. The aim of treating your pet is to reduce the signs of HAC to improve your pet’s quality of life and is best achieved by working closely with your vet.

Shanika Winters MRCVS (online vet)

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