Cushing’s disease, also known as hyperadrenocorticism, is the overproduction of the steroid hormone cortisol. Dogs need naturally produced steroids in order for their bodies to function properly. Cortisol is produced in the adrenal glands near the kidneys. The adrenal glands are controlled by the pituitary gland which sits at the base of the brain.
If any of these glands develops a tumour, then an excess of cortisol is produced, which in turn causes the disease known as Cushing’s. These tumours are usually benign (i.e. don’t spread) but occasionally can be malignant.
The majority of Cushing’s cases in dogs have a growth situated in the pituitary gland, but occasionally this can be in the adrenal gland. The excess of cortisol within the dog is also known as endogenous Cushing’s disease. If a dog is given large doses or long treatments of steroid drugs, this can also induce Cushing’s disease, then known as exogenous Cushing’s disease.
Cushing’s disease is diagnosed fairly frequently in middle-aged dogs. Data from the United States of America estimates that 100,000 dogs per year are diagnosed with Cushing’s disease.
Symptoms of Cushing’s disease include:
Increased thirst and increased urination.
Hair loss – often over the flank but also thinning of the haircoat in general.
Skin problems which may include thinning skin, recurrent skin infections, bumps on the skin which seem gritty (calcinosis cutis) and dark patches or spots of hyperpigmentation.
An enlarged abdomen leading to a pot-bellied appearance.
Generalised lack of muscle.
As a consequence of having Cushing’s disease and if left untreated, your dog may go on to develop high blood sugar levels (diabetes mellitus), high blood pressure, blood clots which have the potential to form in the lungs and cause serious breathing problems (pulmonary thromboembolism), non-itchy skin infections, urinary tract infections and kidney problems.
To diagnose Cushing’s disease, your vet will need to obtain a thorough history and examine the dog. If the index of suspicion is high from these findings, your vet will send blood and/or urine samples to a laboratory for testing. Given the fact that there is often an underlying tumour, your vet may also recommend some imaging, such as an ultrasound, CT or an MRI scan.
Treatment for the disease depends on the underlying cause. If there is a tumour present and no spread, surgery may be performed to remove the entire mass and cure your dog of Cushing’s disease. This may also depend on any other problems your dog may have. If surgery is not an option for your dog, life-long medication will need to be prescribed by your veterinary surgeon. This needs to be closely monitored and adjusted with frequent blood tests.
Radiation therapy may also be indicated to shrink a tumour.
Most commonly the treatment for Cushing’s disease is to manage the syndrome rather than cure it.
Life expectancy is often cited to be around 3 years on medication, although some dogs will happily live much longer.
Once clinical signs are affecting your dog’s daily life and the quality of life is impacted, it is a good idea to discuss end of life care with your veterinary surgeon. If the condition isn’t well-controlled on treatment or if you can’t afford to continue with treatment, then euthanasia may be the most humane decision. As the treatment options involve surgery, radiation or lifelong medication with frequent monitoring (including consultations and blood tests), Cushing’s disease can be an expensive condition to manage.
When to go to a vet
If you notice any changes in your dog’s thirst, toileting, appetite, behaviour, energy levels or overall condition, it is recommended that you seek advice from your veterinary surgeon.