Ageing dogs likely to present
Cushing's disease symptoms

CUSHING'S disease is a well-documented syndrome in the ageing dog, generally from about 10 years of age onwards. Because it strikes older dogs, owners often think that their dog is ageing fast and begin to consider the quality of life their companion is experiencing and the possibility of euthanasia in the near future. However, if the dog has Cushings disease it can sometimes be cured and in most cases controlled. Only a small percentage of cases are terminal. This is because Cushing's can be caused by any one of three sources, and two of the sources require further investigation.

To explain simply - the pituitary gland produces a hormone when stimulated to do so by the hypothalmus in the brain. This hormone travels in the bloodstream to stimulate the adrenal glands to produce its cortisol hormones - usually in order to cope with some form of stress that the body is experiencing at the time. When there is enough cortisol in the blood to cope with the stress levels the pituitary gland stops producing its hormone, and while there is not enough cortisol the pituitary gland will keep excreting its hormone. In a healthy body this maintains a constant balance.

When the dog develops Cushing's, the balance has been disrupted for any of three reasons - there is a tumour in the pituitary gland; there is a tumour in the adrenal gland; or the dog is responding to being over-medicated with steroids. For either of the three reasons the dog is literally being poisoned by too much cortisol in its blood.

Cushing's has always been difficult to diagnose because of the complexities of the tumours. However, most of them are benign. Only in very rare cases are they cancerous, but treatment for the few such cases is of course different to treatment of benign tumours. But first the diagnosis.

If a dog has been on steroids for some time, owners should be immediately suspicious that the steroids are the cause of its Cushing's symptoms. The dog may have been on steroids for a totally different condition such as skin allergies and sometimes a vet may not want to take it off the medication, but before such a dog is treated for either of the glandular Cushing's types it must be assumed as steroid-caused and slowly taken off the steroids to recover. Owners should discuss the dog's treatment with the vet and perhaps suggest non-steroidal anti-inflammatories or diet control instead of steroids. Only if such a dog fails to respond to stopping the steroid treatment should it then begin the Cushing's testing.

If pituitary tumour is the diagnosis from testing these are usually benign and small. But they cause the constant output of the pituitary hormone, which in turn means the adrenal glands have to work constantly to keep up with the demand for cortisol. The tumours can sometimes be larger in size and in this case can cause brain pressure and many other symptoms, some of them resembling the side-effects from the most likely medication. This of course can mean that alternative medications are sought because of side-effects, but in reality it is the size of the tumour causing the problems.

Pituitary tumours can be treated with radiation therapy to shrink them but this is often not an option if the dog has other conditions and is quite elderly - response to anaesthetics is often not good in older dogs. Radiation treatment is also very expensive. So usually pituitary tumours are simply controlled by medication for the dog's remaining lifetime.

When the problem is an adrenal tumour further diagnosis is required because about half of these are benign, the rest being malignant. For dogs with a benign tumour the surgical removal of the affected adrenal gland is often all that is required to put the secretions back on a balanced output. However, if the tumour is malignant it is very likely that the cancer has already spread to the lungs, liver, or any other organ. In such cases the dog can just be made as comfortable as possible for the time it has left.

Medications for controlling pituitary Cushing's include Lysodren, Ketoconazole, and Anipryl. Lysodren has the action of killing off the outer layer of the adrenal glands as the outer layer produces the cortisol. On this treatment the dog is monitored often until the output of cortisol is at normal levels. From then onward the dog may need only occasional doses to maintain that level.

Ketoconazole suppresses the actual production of cortisol. It is a more expensive medication and some dogs can not absorb it but it has low toxicity and is especially good for dogs that experience bad side-effects on Lysodren.

Anipryl helps to restore the natural balance of chemicals in the brain, so gradually brings production back to normal. With a high level of positive results it is the best option for most dogs with pituitary based symptoms.

If not treated Cushing's can progress to diabetes, liver or kidney failure, skin or bladder infections, heart failure or many other life-threatening illnesses, so as soon as Cushing's is suspected take the dog to be examined. Whatever type of Cushings is diagnosed the sooner the dog is treated the better will be its outcome. - EP

Study resources for this article sourced from many veterinary internet information sites. The information is intended to help owners ask the right questions and to be more involved and more assertive when visiting their vet.