Dogs with Cushing’s syndrome produce excessive amounts of cortisol. This can have harmful effects on other organs and on the ability of the body to regulate itself.
Cushing’s occurs in dogs who are producing excessive amounts of cortisol, an important hormone that helps to regulate the body’s metabolism. Cortisol plays a vital role in protein, carbohydrate and fat metabolism and is released into the bloodstream at times of stress to prepare the body for a flight or fight response.
Cortisol is produced by the adrenal glands - two small glands located in the abdomen, next to each kidney. A hormone called ACTH controls the production and release of cortisol from the adrenal glands. ACTH itself is produced by the pituitary gland, a pea-sized gland located at the base of the brain.
The concentration of cortisol in the blood of healthy animals varies greatly as the body’s demands fluctuate. For example, during a period of anxiety or illness, it is normal for the adrenal glands to increase its production. Once this period of stress has passed, the concentration in the blood returns back to normal.
In dogs with Cushing’s syndrome, there is a chronic overproduction of cortisol over weeks and months. Although the concentration of cortisol in the blood of a dog with Cushing’s also fluctuates greatly, it tends to be, on average, much higher than in healthy dogs. The excessive amount of cortisol released into the bloodstream has a harmful effect on the function of many organs and the body’s metabolism.
Most dogs with Cushing’s (approximately 85% of cases) have a benign tumour of the pituitary gland. The tumour cells produce large amounts of the hormone ACTH, which in turn stimulates the adrenal glands to overproduce cortisol. The other cause of Cushing’s (approximately 15% of cases) is a tumour of one (or very rarely both) of the adrenal glands, which produces excessive amounts of cortisol.
Irrespective of the cause of Cushing’s syndrome in your dog, the result is always the same - more cortisol is produced than is actually needed by the body. This results in the slow development of a combination of clinical signs that are classically associated with Cushing’s.
The Importance Of Getting Treatment
If left untreated your dog may develop other serious conditions which will weaken its body and require further costly treatment. Aside from the impact on your dog’s quality of life, if left untreated Cushing’s syndrome increases your dog’s risk of developing several serious conditions such as diabetes mellitus (a deficiency of insulin resulting in high blood sugar), blood clots in the lungs, kidney infection, urinary tract infection and inflammation of the pancreas.
Recognising The Signs Of Cushings Syndrome
Cushing’s is usually seen in older dogs. Small breed dogs are more likely to develop the disease. The most common signs of the disease are very similar to those associated with the normal ageing process. This can make it difficult to diagnose and later monitor. It is always a good idea wherever possible to keep a note of the changes you see in your dog’s habits, behaviour and appearance.
The most noticeable signs of Cushing’s syndrome include:
• Large water intake
• Frequent urination and possible incontinence
• Ravenous appetite
• Pot belly
• Thin skin
• Hair loss or recurrent skin diseases
• Muscle wastage
• Lethargy
• Excessive panting
Not all dogs will react to the disease in the same way and your dog may not necessarily display all of these signs.
Diagnosis
We may suspect Cushing’s disease based on the clinical signs your dog is showing. It is imperative that we get an accurate diagnosis prior to instigating treatment. We will usually start by taking a blood test to check your dogs general health.
The concentration of cortisol in the blood of both healthy dogs and dogs with Cushing’s fluctuates greatly throughout the day. It is for this reason that a diagnosis cannot be confirmed by just one measurement of cortisol. The two tests that are used to confirm a diagnosis of Cushing’s are called the ACTH stimulation test and the low-dose dexamethasone suppression test. It may be necessary to perform both tests.
In the ACTH stimulation test, blood is taken to measure cortisol before and after your dog is given a synthetic version of the hormone, ACTH. This test assesses how well your dog’s adrenal glands control the production of cortisol.
Treatment
Cushing’s syndrome is not curable but it can be very effectively controlled; maintaining a good quality of life for your dog for years to come. Vetoryl is currently the only licensed treatment for use in dogs, it contains the active ingredient trilostane, a drug that rapidly reduces the production of cortisol by the adrenal glands.
Once on medications we will usually perform another ACTH stimulation test after 10 days. This is to ensure that your dog is not getting too much medication and suppressing cortisol production. The results of this test may mean we have to alter the dosage of medications. We would then ideally repeat the ACTH stimulation test after 4 weeks, 12 weeks and then every 3 months after starting treatment.
In most you can expect to see a decrease in your dogs appetite and the amount that they drink within the first couple of weeks on treatment. Other clinical signs may take 3-6 months to improve