Published on May 25th, 2016 | by Debbie Martin0
Understanding Dogs and Cushing’s Syndrome
In mammals like your dog, the endocrine system plays an important role in regulating metabolism. Without the right signalling in place, this metabolism cannot properly function – and all sorts of problems will arise as a result. Unfortunately, the balance of the endocrine system is a very delicate one; as a dog gets older, it becomes increasingly vulnerable to hormonal disorders. Of these, perhaps the most common is Cushing’s syndrome, which causes an affected animal to produce too much cortisol.
Cortisol is a hormone is produced in the body’s two adrenal grands, which are found just beside each kidney. This hormone is responsible for controlling how proteins and carbohydrates are metabolised in the dog’s body. An excess of it can therefore produce a number of knock-on effects for the other organs, and by extension the overall health of the dog.
In a healthy dog, the amount of cortisol in the bloodstream varies tremendously. During times of exertion and stress, the adrenal glands must release more cortisol in order to boost the body’s metabolism. After the stress has passed, the gland returns to normal, and so too does the metabolism of the effected dog. In a dog with Cushing’s syndrome, cortisol levels fluctuate in much the same way – but they’re far higher than usual, and so those spikes in cortisol levels are far more severe.
The release of cortisol controlled by another hormone called the adrenocorticotropic hormone (ACTH), which is produced by the pituitary gland – a much smaller gland nestled just beneath the brain. Consequently, there are two areas of possible weakness – if either the pituitary or adrenal glands are effected by a tumour, then Cushing’s syndrome will usually be the result.
In the vast majority of cases of Cushing’s syndrome, the cause is a benign tumour in the pituitary gland, which stimulates increased production of ACTH. In some other cases, a tumour has usually formed in one or both of the adrenal glands. The end result is the same, however: an increase in overall levels of cortisol. This increase is a chronic one: as cortisol levels build up over many months and years, it gradually places a greater strain on the animal’s organs.
But exactly how does this strain manifest itself? Identifying the early signs of Cushing’s syndrome can actually be quite difficult, since they’re initially very similar to the signs of aging. Let’s run through some of the more obvious signs that your dog might be suffering:
- Constant hunger and thirst
- Weight gain
- Recurrent cystitis
Hormones like cortisol play a vital role in ensuring that the animal’s appetite is at the correct level, and that the food and water they consume is put to good use within the body. When this doesn’t happen, symptoms such as the above are common.
That isn’t to say, however, that they’re inevitable. All dogs are different, and many of them react to Cushing’s syndrome in different ways. One might grow obviously fatter, but develop no cystitis. It’s therefore best to make a mental note of any troubling signs, and watching how those symptoms develop, before concluding that Cushing’s syndrome is the cause.
Naturally, if your dog is constantly lethargic, overweight, or suffering from recurrent bouts of cystitis, then it is a good idea to take it to the vet for a more thorough examination, regardless of whether Cushing’s syndrome is to blame.
As you might imagine, Cushing’s syndrome is not the easiest condition to diagnose. Your vet will inspect the dog for clinical signs of the disease, but ultimately the diagnosis will only be confirmed after a blood test. This will give an indication, not only of the presence of the syndrome, but of the animal’s overall state of health.
Unfortunately, things are complicated still further when we consider the constantly-fluctuating nature of blood-borne hormones. If we take the measurement while cortisol levels are spiking, this might suggest that they’re higher than they actually are.
For this reason, a single blood test is not enough to confirm the diagnosis; we must use further tests in order to do that. In the main, there are two different tests used to confirm the presence of Cushing’s syndrome. Let’s look at them in turn:
ACTH stimulation test
This test involves giving your dog an artificial injection of the ACTH hormone. By measuring the levels of cortisol before and after this dose is administered, the vet can see how your dog’s adrenal glands respond to it.
Low-dose dexamethasone suppression test
This test works in entirely the opposite way to the ACTH test. Dexamethasone is a variety of steroid medication which inhibits the pituitary gland’s ability to produce ACTH. Before and after administering the medication, the vet can again measure for changes in cortisol levels, and use that as a basis for diagnosis.
In addition to these tests, a vet might establish the presence of a tumour on the pituitary or adrenal glands using x-ray and ultrasound imaging.
Once we’ve established that a dog is suffering from Cushing’s syndrome, it’s important to take steps to control the disease’s development. If left unchecked, it can easily cause further problems, like diabetes, pancreatitis and further urinary tract infections.
Unfortunately, there’s no way of curing the problem with medication. We can, however, surgically remove the tumour responsible. Your vet will be able to advice whether this is feasible, and which medications will confer the greatest benefit, and the lowest side-effects.
If you’re going to treat your dog with medication, then you’ll need to monitor them for potential side effects. Adverse reactions might be evidenced by weakness, diarrhoea or a marked lack of appetite – if such signs should manifest themselves, then be sure to discontinue treatment immediately and return to your vet.
If your goal is to manage your dog’s symptoms rather than removing the tumour surgically, then you should be prepared to live with the condition for the remainder of your dog’s life. But if your dog is already very old, then surgical procedures might be more trouble than they are worth. Be sure to discuss the available options with your vet before deciding how to proceed – with the right management, there’s no reason that an afflicted dog can’t lead a happy life.