Hyperadrenocorticism (Cushing’s) is caused by an excess production of stress hormone (cortisol) from the adrenal glands which sit near to the kidneys in the abdomen.
There are two main reasons for Cushing’s disease:
- The most common reason is called Pituitary-dependent Hyperadrenocorticism. This is where the pituitary gland in the brain produces excessive amounts of adrenocorticotropic hormone (ACTH) most commonly due to a small growth. The ACTH then travels to the adrenal glands in the blood and stimulates them to produce excess amounts of cortisol.
- The second reason for Cushing’s disease is an Adrenocortical tumour. This is where the adrenal gland enlarges due to the tumour and the larger volume of the gland will produce more cortisol.
- Cushing’s disease can also be stimulated by giving the patient glucocorticoids (some steroid medications). If the body cannot cope with the medication it can cause symptoms of Cushing’s disease. This is known as Iatrogenic Cushing’s.
Frequently Asked Questions
What are the symptoms of Cushing’s disease in dogs?
Depending on the duration of the disease more or less symptoms may be present. The most common symptoms are listed first.
- Excessive drinking and urination
- Increased appetite
- Enlarged abdomen - potbellied appearance due to fat re-distribution
- Skin changes e.g. thin skin, skin infection, hair loss, calcified hard skin plaques, pigmentation
- Muscle wastage, weakness and tremors
- Neurological signs e.g. ataxia (wobbliness), stupor, circling, aimless wandering, pacing and other behavioural changes
How is Cushing’s diagnosed?
Diagnosis is not always straight forward for hormonal diseases.
Blood tests are normally recommended following clinical examination by a vet and assessment of the above symptoms. Sometimes a routine blood test can highlight a suspicion of a hormonal disease such as Cushing’s so further blood tests may be recommended. However, blood results can sometimes be equivocal therefore repeat tests may need to be performed.
The main blood test in diagnosing Cushings is the ACTH stimulation test which is a dynamic test measuring the cortisol levels in response to an injection of synthetic ACTH. Blood samples need to be taken before the injection and again 2 hours afterwards to measure the body’s response.
A Dexamethasone suppression test can also be used to check for Cushing’s disease.
An ultrasound of the abdomen can be helpful to identify adrenal tumours and the general size of the glands. If the glands are larger than average, then this gives a stronger suspicion of Cushing’s disease.
MRI and CT examinations can be helpful to assess for growths in the adrenal glands and the pituitary gland in the brain.
What are the treatment options for Cushings in dogs?
80-85% of dogs with Cushing’s disease have pituitary dependent hyperadrenocorticism. These can be managed on medication alone.
Capsules are normally given daily depending on the weight of your pet. Because the condition is to do with hormones the dose often needs adjusting once treatment has been started, so we normally recommend an ACTH stimulation test 10 days, 4 weeks, 12 weeks then every 3 months after starting therapy. If adjustments are made to the dose, then repeat blood tests 3-4weeks afterwards are necessary.
Dogs that have been diagnosed with a pituitary tumour and are showing neurological symptoms may benefit from radiation therapy.
For dogs that have an adrenal tumour, surgery to remove the tumour may be considered. This should be discussed in more detail with your vet.
What is the prognosis for my dog with Cushing’s disease?
Most dogs with pituitary dependent hyperadrenocorticism have a normal life expectancy when treated.
Dogs with adrenal dependent Cushing’s disease who have an adrenal tumour removed have a life expectancy of around 36months. Some types of tumours have a better prognosis than others and it depends if the tumour has already spread at the time of diagnosis.