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What is Cushing’s Syndrome (Hyperadrenocorticism)?
Cushing’s Syndrome, also known as hyperadrenocorticism, is a disease caused by excessive production of cortisol. Cortisol is a very important hormone that the body needs on a day-to-day basis, but its levels need to stay within a normal range that the body normally regulates. Cortisol is produced by the adrenal glands, two small glands located near the kidneys in the tummy (abdomen). The adrenal glands are stimulated to produce cortisol by another hormone (called ACTH) which is released by the pituitary gland, a very small gland located in the lower part of the brain.
Why do dogs get Cushing’s Syndrome?
Cushing’s Syndrome occurs due to excessive amounts of cortisol in the bloodstream. The condition can be caused by:
- a very small tumour of the pituitary gland (this is the most common form). These tumours are usually so small that the tumour itself is not otherwise harmful
- a large tumour of the pituitary gland (this is uncommon)
- tumours or benign enlargement of one or, rarely, both of the adrenal glands next to the kidneys
- administration of too much of a medication called corticosteroids e.g. prednisolone or dexamethasone
What are the symptoms (signs) of Cushing’s Syndrome?
- increased thirst
- increased frequency and volume of urination
- increased appetite
- weight gain
- thin skin, and sparse hair coat
- ‘pot belly’
- muscle wastage
- calcification of the skin or ligaments
- excessive panting
- being prone to infections
- uncontrolled diabetes (see Diabetes mellitus information sheet)
How is Cushing’s Syndrome diagnosed?
Cushing’s Syndrome can be very hard to diagnose. The disease can have similar symptoms to several other diseases such as diabetes, hypothyroidism and urinary tract infections. Cushing’s Syndrome is suspected after we have taken a full history and performed a detailed physical examination, but further tests are required to confirm the diagnosis.
Cortisol is normally present in the bloodstream, levels of cortisol increase whenever the body is ‘stressed’ (i.e. by illness, external strains or anxiety). A single blood cortisol test does not tell us if a pet has Cushing’s Syndrome, because numerous situations can lead to an increase in cortisol. We use the combination of urine tests, blood tests and ultrasound scans of the abdomen (tummy) to diagnose Cushing’s Syndrome.
Routine blood screening in pets with Cushing’s Syndrome often shows:
- raised liver enzyme activities (these are chemicals produced by the liver)
- increased cholesterol in the blood
- increased white blood cell counts (the blood cells which fight off infection)
- occasionally, increased calcium levels
These findings are not specific to Cushing’s Syndrome, as they not uncommonly occur in other diseases. To refine our diagnosis, we perform what is called ‘dynamic blood testing’ – most commonly an ACTH stimulation test, or a low-dose dexamethasone suppression test. These tests help us to assess the function of the adrenal glands, and their ability to increase or decrease cortisol production. These tests require your pet to be admitted into hospital for the day. An initial blood sample is taken to measure the baseline cortisol level. An injection of ACTH or dexamethasone is then given, and further blood samples are taken to measure the response of the adrenal glands to these substances. The procedure is quite simple and doesn’t hurt your pet. Specialised blood tests (e.g. measuring the levels of other hormones such as the body’s natural ACTH produced by the pituitary gland) can also aid in making the diagnosis.
In addition to performing blood tests, diagnostic imaging may be required in some cases. For example, an ultrasound scan of the abdomen can show whether one or both of the adrenal glands is enlarged, and occasionally adrenal tumours can be diagnosed on the scan. An MRI or CT scan of the brain is occasionally needed to determine if there is a large pituitary gland tumour present.
How is Cushing’s Syndrome treated?
Cushing’s Syndrome is usually treated medically, or by surgery in some cases. We most commonly use medication to manage Cushing’s Syndrome, as modern drug treatment can often successfully reduce cortisol production. Cushing’s Syndrome is not curable but can often be successfully managed by using medication which is given for life.
Medical treatment of Cushing’s Syndrome
The most common medication used in the UK to treat Cushing’s Syndrome is trilostane (Vetoryl®). This treatment is given once or twice a day as a capsule. Trilostane reduces the production of excessive amounts of cortisol. It can have powerful effects, and it is therefore very important that we regularly measure the amount of cortisol produced. Too much medication can lead to inadequate amounts of cortisol in the bloodstream, creating a life-threatening-crisis (hypoadrenocorticism or Addison’s disease). On the other hand, too little medication can lead to poor control of the disease and ongoing symptoms. Blood tests need to be performed at intervals to measure the body’s response to treatment. Your vet will advise you how frequently blood tests need to be performed. In most patients the dosage of trilostane needs to be adjusted as time goes by.
Surgical treatment of Cushing’s Syndrome
Surgery to remove the adrenal gland(s) is sometimes required to control the disease process in certain cases of Cushing’s Syndrome. This surgery is complicated and is performed by our Specialist team of anaesthetists and surgeons. If surgery is an option, we will discuss this in detail with you to ensure that you are fully informed of all the significant implications of the procedure.
What is the long term outlook for Cushing’s Syndrome?
Although Cushing’s Syndrome is quite a serious disease which can affect life expectancy, we will do all we can to enable your dog to enjoy a good quality life, hopefully for a long time to come. In most cases, the earlier the condition is diagnosed and the more closely the effects of treatment are monitored, the better the outlook will be. Can cats get Cushing’s Syndrome? Cushing’s Syndrome is very rare in cats.
If you have any queries or concerns regarding your pet and Cushing’s Syndrome, please do not hesitate to contact us.