Canine Cushing's Syndrome (Hyperadrenocorticism)
What is Cushing's syndrome?
Dogs with Cushing's syndrome produce too much cortisol; this can have harmful effects on other organs and on the ability of the body to regulate the metabolism. Cortisol plays a very important part in protein, carbohydrate and fat metabolism and is released into the blood stream at times of stress to help the body cope.
Cortisol is produced by the adrenal glands (two small glands in the abdomen which lie next to each kidney). A hormone called ACTH (adrenocorticotrophic hormone) controls the production and release of cortisol from the adrenal glands. ACTH is produced by the pituitary gland, a small pea-sized gland located at the base of the brain.
The amount of cortisol in the blood of healthy animals varies greatly as the body's demand for cortisol changes. For example, during a period of anxiety or illness, the adrenal glands produce increased amounts of cortisol. Once this period of stree resolves, the cortisol level in the blood will drop back to normal.
In dogs with Cushing's syndrome, there is a CHRONIC (long-standing) overproduction of cortisol over weeks and months. Although the level of cortisol in the blood of a dog with Cushing's syndrome also fluctuates greatly, it tends to be on average much higher than in healthy dogs. The excessive amount of cortisol released into the blood stream has a harmful effect on the function of many organs and the body's metabolism.
What causes Cushing's syndrome?
Cushing's will usually occur as a result of a tumour – usually benign – of either the pituitary gland (most common) or of the adrenal glands (less common). Regardless of its cause, over time a dog with Cushing's will develop a combination of clinical signs which may be associated with too rapid ageing.
Most dogs with Cushing's (about 85% of cases) have a benign tumour of the pituitary gland. This tumour produces large amounts of ACTH, which in turn stimulates the adrenal glands to overproduce cortisol.
The other cause of Cushing's (about 15% of cases) is a tumour of one, or very rarely both, of the adrenal glands, which then overproduce cortisol.
Irrespective of the underlying cause, the result is always the same; too much cortisol is produced. This results in the slow development of the clinical signs that are classically associated with Cushing's syndrome.
Why do I need to get my dog treated?
If left untreated, your dog may develop other serious conditions which will weaken its body and could require further difficult and expensive treatment. Aside from the impact on your dog's quality of life, if left uncontrolled, Cushing's syndrome increases your dog's risk of developing several serious conditions such as diabetes mellitus , blood clots (thromboembolism), kidney infections, urinary tract disease and inflammation of the pancreas.
How do I recognise the signs of Cushing's syndrome?
Cushing's is more commonly seen in older dogs and smaller breeds of dog. Hair loss, pot-belly, skin diseases, changes in behaviour, frequent urination and a ravenous appetite can all be associated with the disease. It is important to stress that not all cases will develop all the signs; presentation can be quite variable. Most of the commonest signs are very similar to those associated with normal ageing. This can make it difficult to diagnose and later monitor.
What are the commonest signs of Cushing's syndrome?
- Increased water intake
- Frequent urination and possible urinary incontinence
- Ravenous appetite
- Thin skin
- Hair loss or recurrent skin infections
- Muscle wastage
- Excessive panting
How is Cushing's syndrome diagnosed?
Your vet will probably suspect Cushing's syndrome initially based on the clinical signs your dog is showing. Sometimes it will be suspected because of typical changes seen in the results of a routine blood test. In most cases, the changes in your dog's appearance and behaviour caused by Cushing's occur very gradually, making them easy to overlook.
Once your vet suspects Cushing's, he/she will need to perform some blood tests to confirm the diagnosis. A blood test to check your dog's general health is also recommended.
Two tests are commonly used to confirm Cushing's syndrome; the Low Dose Dexamethasone Suppression Test and the ACTH Stimulation Test. It may be necessary to perform both tests to be certain of the diagnosis. The ACTH Stimulation Test takes about 1 hour and is usually used to monitor the response to treatment; the Low Dose Dexamethasone Suppression Test is usually used for diagnosis purposes; this test takes about 8 hours to do.
How is Cushing's syndrome managed?
Cushing's disease cannot usually be cured, but it can be very effectively controlled medically, but treatment is ongoing for the rest of your pet's life. The drug that is used is called Vetoryl ™ (active ingredient trilostane) and this rapidly reduces the production of cortisol by the adrenal glands.
Occasionally, in cases of adrenal dependent Cushing's (only 15% of cases) surgical removal of an affected adrenal gland has been performed, but this is a high-risk procedure that relies on accurate confirmation of which adrenal is affected. It is rarely attempted now that medication is so safe and effective.
Your dog will begin to take Vetoryl ™ at the recommended starting dose depending on its bodyweight. You should then make an appointment for your dog to see the vet after about 10 days. Your dog should be regularly examined and monitored using blood tests.
Your vet will assess your dog's response to treatment by:
- Looking for an improvement in clinical signs; for instance, a reduction in water intake and/or appetite within the first few weeks of treatment. Other signs (eg. skin/hair changes) can take 3 to 6 months to improve.
- Performing blood tests; the results of routine blood tests and an ACTH stimulation test are used to monitor the effectiveness and safety of Vetoryl ™ treatment at 10 days, 4 weeks, 12 weeks and then every 3 months thereafter.
What do I need to know about Vetoryl ™?
- Vetoryl ™ comes in a range of capsule sizes; your vet will advise you of the right size for your dog. It is recommended that Vetoryl ™ is given with a meal in the morning, as this will make it easier for your vet to perform monitoring tests 4-6 hours after dosing.
- If you forget to give a capsule, DO NOT give double the dose the next day.
- Most dogs will need lifelong mediation with Vetoryl ™.
- Vetoryl ™ is well tolerated by most dogs. However if your dog develops any signs of illness whilst on the medication such as lethargy, vomiting, diarrhoea and anorexia, stop treatment immediately and contact your vet for advice.
- Vetoryl ™ capsules should NOT be split.
- Vetoryl ™ capsules should NOT be handled if you are pregnant or trying to conceive.