Canine Cushing’s (CCD) disease appears to be a disease on the rise. DW readers often ask for information about the syndrome and the ever-present question is about inheritance. The term ‘Cushing’s Disease’ is something of a human medicine ‘hand-me down’ in the terminology sense but the disease in dogs has its own specific characteristics.
It is really a syndrome meaning there are a series of symptoms leading to the diagnosis but these can be highly variable in individual cases. The root cause of the symptoms is the over production of cortisol, an essential hormone acting as a central factor in body physiology.
Cortisol is a glucocorticoid hormone.
In understandable English this means it is a hormone that affects the metabolism of glucose. However it also has many other effects. Regular readers will recall glucose is an important fuel for cellular energy.
Cortisol has potent anti-inflammatory abilities and this has been utilised in the development of medicines like cortisone, which are commonly used for their ability to reduce inflammation and thus pain. However, cortisone (or any of its chemical relatives) is capable of causing many side effects and these are all represented in the broad range of symptoms associated with CCD too.
For example, cortisol stimulates appetite, in excess leading to obesity. It makes an animal thirsty and thus secondarily increases urination through increased water intake.
Over prolonged periods, increased cortisol will also reduce the thickness of skin, or associated obesity leads to a distinctive potbelly. Cortisol also suppresses the immune system.
Long-term, high levels of cortisol can cause hair to thin, soften and loose colour. It produces neurological effects with lethargy being high on the list. The ability of an imbalance of cortisol to produce this range of adverse effects simply reflects the central role that this hormone usually plays in normal body function.
Why does this over-production of cortisol occur in CCD? There are two possible reasons and both involve a tumour. The first is a tumour in the adrenal gland. There are two adrenal glands each one lying close to a kidney. These glands secrete the hormone cortisol. A tumour involving the glandular cells in either adrenal gland will produce higher than normal amounts of the hormone.
The second type of tumour arises in the pituitary gland. The pituitary gland secretes another important hormone called ACTH (adrenocorticotropic hormone) to stimulate the adrenal glands to secrete cortisol. This tumour is found in the pituitary glandular cells and produces abnormal amounts of ACTH.
Some 80 per cent of CCD cases are pituitary in origin with a pituitary tumour being more common in small breeds and the adrenal gland tumour being dominant in larger breeds. Further interesting information suggests that in large dogs there is a higher incidence in bitches but this sex bias is not seen in smaller dogs. However, the site of the tumour is largely academic as, although the tumour is the root cause of the disease, the clinical effects are the same in both forms.
So how do we recognise CCD? The typical case is six years old or more. The challenge with CCD is noticing its effects early in the course of the disease. Early detection may increase the opportunity to treat successfully.
The syndrome is characterised by slow progression where owners frequently mistake significant changes as age related.
After all you might expect an older dog to drink a little more and many dogs have large appetites and carry too much weight. As dogs get older they tend to slow up and perhaps they pant a lot because they have too much coat. A loss of coat lustre and colour is surely another sign of advancing years?
This is how many cases develop. It is often only at a health check, or when the dog gets an infection that is slow to respond, or a chronic skin condition associated with scabbing and colour change, that owners may come to realise that something more serious is happening.
Even when the symptoms are highly suggestive and typical of CCD, diagnosis can be difficult. The tests that can be done are not always entirely conclusive. Nevertheless, once diagnosed the treatment options are reasonable with many cases responding well. However the dosage can be difficult to get right.
The medicines used either block the production of cortisol or destroy the tumour cells that secrete hormone. The ambition of therapy is to give sufficient drug to reduce the cortisol levels to normal and keep them stable. This is not always easy to achieve. Some dogs may not respond at all or alternatively a patient can suffer a cortisol deficit which produces its own serious forms of illness (remember cortisol is essential element of life).
Surgical removal of an adrenal gland affected by a tumour can be considered but clearly if the tumour is in the pituitary gland it is not readily accessible and medical therapy is the best option. However be aware that diagnosis, clinical tests and treatment are certainly not cheap.
Medication is given daily for the rest of life and progress requires extensive and repeated expert monitoring. So before embarking on this course of action the whole picture needs to be taken into consideration. By way of example, an elderly dog may have other complicating factors.
It is not unusual for dogs with CCD to also suffer from diabetes, chronic kidney or liver disease or other diseases commonly associated with advancing years. In addition pancreatitis and chronic infections, including urinary tract disease, are complications found associated with CCD. They may persist even if the adverse effects of the cortisol are countered.
The surgical option may be ruled out if a depressed immune system is likely to compromise healing. Because of the slow, progressive nature of CCD, elderly dogs with less severe signs might be best treated symptomatically rather than risk attempting to reverse the core disease. For example managing obesity or a skin problem may keep them comfortable for the lifespan they have left.
The conclusion is CCD is not easy to diagnose or treat and owners need to be aware that management of CCD is an on-going effort by owner and veterinary surgeon to best manage a dog’s health. On occasions it may not be successful.