Cushing's Disease -
hyperadrenocorticism
(5min read)
What is cushing's disease?
Cushing’s disease is caused by prolonged exposure of the body’s tissues to high levels of the hormone, cortisol. Cushing’s disease is also called Hyperadrenocorticism.
Cushing’s disease is caused by an excess of the steroid hormone, cortisol. In the normal dog cortisol is produced by the adrenal glands, (which are located just in front of the kidneys). Scientists think that cortisol has hundreds of possible effects in the body. Among its other vital tasks, cortisol helps to:
maintain blood pressure.
slow the immune system’s inflammatory response.
balance the effects of insulin in breaking down sugar for energy.
regulate the use of proteins, carbohydrates and fats in the body.
Because cortisol is so vital to health, the amount of cortisol produced by the adrenal glands is precisely balanced. Cortisol production is regulated by hormones produced in the brain (from the pituitary gland). The hormones produced by this gland stimulate the adrenal glands. When the adrenal glands receive the signal from the pituitary they respond by producing cortisol. In the normal animal cortisol is produced mainly at times of stress – in Cushing’s disease the levels of cortisol in the blood are always too high.
What causes Cushing's Disease
Nearly all cases of Cushing’s disease are caused by a tumour in the pituitary gland. Although this is, strictly speaking, a brain tumour the tumour is usually tiny and benign and usually causes no other ill effects apart from the over production of cortisol. A few cases of Cushing’s disease are caused by a tumour in the adrenal gland.
The two forms of natural Cushing’s disease are:
Pituitary-dependant Cushing’s disease
A tumour in the pituitary causes excess production of the hormone, adrenocorticotropic hormone (ACTH) resulting in enlargement of both adrenal glands.
Adrenal-dependant Cushing’s disease
A tumour of the adrenal gland makes one gland grow bigger and it is therefore able to produce more cortisol.
Sometimes signs of Cushing’s disease are caused by steroids given by the veterinarian to treat another disease eg allergic skin disease.
How would I know if my dog has Cushing's?
The signs of Cushing’s disease are extremely variable and can be subtle in the early stages. It is usually not possible to decide which form of the disease is present by the clinical signs. Cushing’s disease affects older pets (over 7 years of age).
Common signs of Cushing’s disease
The steroid hormones affect almost every tissue in the body and the signs of Cushing’s disease can be diverse. Dog’s may have only one or can have several signs of Cushing’s disease, the most common are:
Increased drinking and urination (e.g. suddenly needing to get up in the night to urinate)
Increased appetite (and weight gain)
Increased panting (even when not hot)
Patchy hair loss (particularly over the flanks) and thinning haircoat without itchiness
Thinning of the skin – poor healing
Muscle wasting/weak muscles
Pot-bellied appearance (where abdomen hangs down more than normal)
Repeated infections and slow healing of wounds
In most cases of pituitary-dependent disease the tumour in the brain is tiny and causes no physical effects. However, in a few animals the brain tumour is sufficiently large such that it can cause neurological signs eg depression, blindness or seizures.
How will my vet diagnose Cushing's?
Cushing’s disease can be very difficult to confirm. Your veterinarian may suspect the disease based on clinical signs and simple blood tests but specific blood tests are needed to confirm the diagnosis. These special tests measure the level of cortisol in the blood. However, because the levels of this hormone vary from hour to hour in a normal animal, the disease cannot be diagnosed on the basis of one blood test. Your veterinarian will need to take a number of blood samples before and after injection of hormones that affect the amount of cortisol produced by your dog. Some of these blood samples have to be handled very carefully and will need to be sent away to veterinary laboratories for analysis.
Ultrasound examination of the abdomen allows your veterinarian to measure the size of each adrenal gland. If a tumour is present in the adrenal gland this should be visible on the ultrasound (and one adrenal gland will appear larger than the other). If the disease is caused by a tumour in the brain then both adrenal glands will be larger than normal. X-rays may also be needed to show other potential problems caused by the disease.
How can the disease be treated and what are the risks?
The most common medication used to treat Cushing’s disease is Vetoryl (Trilostane). This is a drug that inhibits the adrenal glands’ ability to produce cortisol. Unlike older treatments for Cushing’s disease it does not destroy adrenal tissue. It is important to realise that this drug does not do anything to treat the tumour (pituitary or adrenal) causing the disease but it can be used to control the signs of cortisol excess in dogs with both pituitary and adrenal dependent Cushing’s syndrome. The drug is given as a tablet once (or sometimes twice) daily and it must be given regularly or hormone levels will rapidly rise again. Monitoring blood tests are required to ensure the correct dose of Vetoryl is found for your dog. The dose will often need to be changed over time depending on your pet’s response.
In a few cases, surgical removal of an adrenal tumour is possible. However this quite a complicated and risky surgery. Your veterinarian may want to start medical treatment before surgery to help decrease the side-effects of high cortisol levels during anaesthesia and surgery.
If your dog has signs associated with a mass in the brain, they will need additional treatment; as the drugs available will not affect the size of this tumour. Radiotherapy is available at some specialist hospitals and this can help shrink the tumour and eventually decrease the levels of ACTH and cortisol in the blood. Unfortunately, because of its location, surgical removal of the tumour in the brain is usually not possible in Cushing’s disease.
There are few reported side-effects from trilostane – provided that careful monitoring is performed. The main risk with trilostane is if the dose is too high and the cortisol levels become too low. Dog’s with low cortisol levels can become quite unwell. Close monitoring of dogs receiving treatment is very important, particularly in the early stages. If your dog has recently started on trilostane or had a recent dose change and shows any signs of vomiting, diarrhoea, lethargy (tiredness), reduced appetite or collapse they will need to be assessed immediately to ensure their cortisol levels are not too low.
Is it worth treating my dog?
Most dogs with Cushing’s disease are middle-aged or elderly and owners sometimes ask if it is worth treating them. Once an animal with Cushing’s disease is stabilized on treatment they will usually live a normal life (simply taking their tablets on a regular basis). The outcome for dogs with pituitary-dependent Cushing’s disease with treatment is very good. Some signs will disappear quickly and others more gradually. Appetite and water consumption usually return to normal in a few weeks; whereas full return of the fur may take several months. Many dogs go on to live a normal lifespan. Without treatment the complications can be significant and will seriously affect the quality of your pet’s life.
What ongoing monitoring is needed?
Frequent monitoring is needed, especially in the early stages of Cushing’s disease treatment. Cortisol level monitoring (ACTH Stimulation test) is needed initially 10-14 days after starting the medication or changing the medication dose. Once the correct dose is found another blood test is needed after 1 month, then 3 months. Once your pet is on a stable dose, they will need less frequent monitoring but will still require 6 monthly consultations with your Veterinarian to continue to dispense the medications and closely monitor your pet. After the initial tests your Veterinarian will advise when repeat testing is required depending on how your dog has responded, in general this will involve:
Repeat Cortisol Levels (ACTH stimulation test) – every 6 months
General Blood test Monitoring – every 6 months (to monitor organ function)
Repeat Abdominal Ultrasound – every 12 months (more frequently in the case of adrenal tumours)
Blood Pressure check – 6-12monthly
If you have any concerns or notice any changes in your pet’s condition please contact your Veterinarian immediately to make a recheck appointment.
