What do you think is the most common hormonal disease of dogs? Diabetes? Thyroid?
In our Adelaide clinic it’s easily Cushings Disease, also called Cushings Syndrome or Hyperadrenocorticism.
What Is Cushings Disease?
Simply, it’s caused by an excess in the body of the hormone cortisol, or artificial substitutes like prednisolone.
Cortisol is a hormone with many functions. It:
- increases blood sugar
- suppresses the immune system
- aids in the metabolism of carbohydrates, protein and fat
- decreases bone formation
Which Dogs Get Cushings Disease?
All dogs can get Cushings disease, but the following breeds have an increased risk:
- Miniature Poodle
- Bichon Frisé
- Yorkshire Terrier
- Toy breeds in general
There is no increased risk in desexed dogs, but males and females are at equal risk.
Obesity may increase the risk. If your dog is gaining weight, this page is here to help.
What Does Cushings Disease Look Like In Dogs?
Excess cortisol causes many symptoms. In order of how often we see them, they include:
- Drinking a lot of water
- Increased appetite or hunger
- Thin hair and hair loss on the back, sides and rump
- Pot belly
- Less interest in play or exercise
- Increased weight
- Panting even in cool conditions
- Urinary infections
- Blackheads (comedones)
- Thickened patches of inflamed skin caused by calcium deposition
- Loss of fertility
- Thin skin & slow wound healing
It’s interesting to compare these with the signs of hypothyroidism. These days, with the increased use of annual screening blood tests, a raised Alkaline Phosphatase enzyme allows us to suspect and diagnose the disease before anyone is aware it’s there.
What Causes Cushings Disease?
There are three sources of the excess hormone:
- Pituitary Dependent Hyperadrenocorticism (PDH)
- Adrenal Tumour (AT)
- Iatrogenic Hyperadrenocorticism (IH)
PDH is caused by a small, usually benign, tumour in the pituitary gland, which is located at the base of the brain. The tumour produces too much of the hormone ACTH which in turn tells the adrenal glands to make too much cortisol.
AT is a simple tumour in the adrenal gland itself. This time it’s the tumour cells themselves that produce too much cortisol. Later you’ll see why this matters.
IH is a bit of an ‘oops’ moment. This form used to be very common when cortisone, prednisolone, triamcinolone or dexamethasone were used a lot to treat canine skin disorders. The overuse of these drugs mimics natural Cushings disease symptoms. Nowadays there are many better ways to treat skin problems in dogs but sometimes IH can’t be avoided when we treat an autoimmune disease.
How Do We Diagnose Cushings Disease?
Vets mostly use either the ACTH Stimulation Test or the Low Dose Dexamethasone Suppression Test (LDDST).
We mostly use the ACTH Stim test for diagnosis as it’s the same one we then use to monitor your dog’s progress. The LDDST is a more sensitive test we may use when the situation is unclear, though it can sometimes cause false positive results from other illnesses. Cushings tests require at least half a day in hospital and a series of injections.
How To Treat Cushings Disease In Dogs
Treating the IH form is easy: just withdraw the drug. Notice we didn’t say stop. If a dog is on cortisone drugs for a long time, it causes the body’s own cortisol production to stop and the adrenal gland to shrink via a feedback loop.
If you stop the drug cold turkey, you will cause a severe and often fatal adrenal crisis called Addison’s Disease. Talk to your vet about slowly tapering the drug in a controlled manner.
To treat PDH or AT you really need to know which form it is. To do this, all we need to do is schedule an abdominal ultrasound examination. Any trained ultrasonographer should be able to easily locate and carefully examine the adrenal glands. You can see some adrenal ultrasound pictures here.
If the adrenal glands are both evenly enlarged, it’s PDH. If one gland is irregularly enlarged, and the other one shrunken, it’s AT.
Treating AT can be easy or hard. If it’s nicely isolated then it’s a reasonably simple surgery to remove an adrenal tumour. The problem is that the adrenal gland nestles next to the aorta and vena cava, the two major blood vessels in the body. If the tumour has spread into these (usually already detected on ultrasound) we can’t operate.
Dogs with inoperable AT, or those awaiting surgery, often still respond well to trilostane…
Dogs with PDH have a good prognosis. The pituitary tumour is not yet able to be removed in Australia, but it shouldn’t cause any other problems.
We use drugs to either suppress the production of cortisol or block its action in the body.
The only drug registered for the treatment of cushings disease in dogs in Australia is trilostane. It’s also the safest. For these reasons, we’ll always recommend using this drug first.
It works by blocking the action of cortisol at the receptor sites in the body.
Advantages are the high safety index, the reversibility when stopped and good results (and the legislative protection for us vets!). It’s also a very good drug to use when planning AT surgery.
The main disadvantage is cost when compared with the older treatment. There is also a reported occurrence of acute adrenal necrosis when using trilostane, which we have seen twice without serious consequences.
For decades this was the treatment of choice until the availability of trilostane. It is a form of specific chemotherapy which targets the adrenal gland. By giving just the right amount, we selectively destroy or deactivate a percentage of the adrenal gland until it produces the right amount of cortisol.
You can see why this drug is more dangerous; too much can cause irreversible damage. It’s also not licensed in dogs, meaning vets have to obtain informed consent for its use. Owners need to take full responsibility for any unforeseen or harmful effects resulting from its use and indemnify the vets from any blame.
We still use mitotane in three situations, when:
- Trilostane treatment produces unsatisfactory results
- The cost of trilostane is unacceptable to a dog owner
- Giving tablets is very hard or unsafe
Long-term therapy with mitotane is possible with only one or two doses per week, instead of daily doses with trilostane.
With both treatments, frequent monitoring is essential. Cortisol is a vital hormone in the body, and overdosing with either drug can be fatal.
Cost Of Treatment
The following comparision is at 2016 prices and applies to a 6.5kg dog on average doses. This is a guide only, individuals will vary greatly.
Mitotane costs $13.40 per week
Trilostane costs $29.20 per week
Initial monitoring costs are, however, higher for Mitotane use. Typically, four ACTH stimulation tests (each costing $250) are needed, whereas two or three are usually adequate for trilostane use. After this, monitoring costs are much the same.
How Successful Is Cushings Treatment?
Very. We like diagnosing and treating Cushings Disease in dogs because we know how much most dogs will improve.
The onset of symptoms is slow and often thought to just be the effects of ageing.
Inside most dogs with cushings syndrome is a playful, active & healthy puppy just waiting for you.