Cushings Disease

Cushing's Disease

What is Cushing's Disease?
Cushing's Disease is a disease in which the adrenal glands overproduce certain hormones. The correct medical term for this disease is hyperadrenocorticism.

The adrenal glands produce several vital substances which regulate a variety of body functions and are necessary to sustain life. The most widely known of these substances is cortisol. Either excessive or deficient production of these substances may be life-threatening.

How does this disease occur?
There are three mechanisms by which this disease can occur. Regardless of the cause, the clinical signs are essentially the same. It is important to identify the cause, however, because the various forms are treated differently and have different prognoses.

1. Pituitary gland tumour The most common cause of Cushing's Disease (85% of all cases) is a tumour of the pituitary gland. The tumour may be either benign or malignant. The tumour causes the pituitary to overproduce a hormone which stimulates the adrenal glands. Excessive cortisol secretion results. The tumour may be either microscopic or quite large. Depending on the size of the tumour, the presence of signs other than Cushing's will be variable. Generally, if the activity of the adrenal gland can be controlled, the dog will live a relatively normal life. Unfortunately, this is sometimes not the case. However, many dogs with this form of Cushing's Disease can live normal lives for many years as long as they take their medication and stay under close medical supervision. Growth of the pituitary tumour would give the patient a less favourable prognosis.

2. Adrenal gland tumour Cushing's Disease may be the result of a benign or malignant tumour of the adrenal gland. If benign, surgical removal cures the disease. If malignant, surgery may help for a while, but the prognosis is less favourable than for a benign tumour.

3. Iatrogenic Cushing's Disease - this term describes the cases of Cushing's Disease that are caused by the excessive or prolonged administration of synthetic corticosteroids used for treating other diseases, (skin disease, for example). This may occur following the use of oral or injectable steroids. Occasionally use of ointment containing cortisone or its derivatives over a long period of time can result in excessive intake due to absorption through the skin or eyes or to the dog licking the product.

What are the clinical signs?
The most common clinical signs associated with Cushing's Disease are a tremendous increase in appetite, water consumption, and urination. Lethargy, or lack of activity, and a poor hair coat are also common. Many of these dogs develop a bloated appearance to their abdomen due to an increase of fat within the abdominal organs and a stretching of the abdominal wall as the organs get heavier. The pot-bellied appearance also develops because the muscles of the abdominal wall become weaker. The skin frequently appears paper thin. Panting is another common finding with this disease.

How is it diagnosed?
A number of tests may be necessary to confirm a diagnosis of Cushing's Disease and further tests may be needed to decide which form of the disease is present. All these tests involve taking blood samples, sometimes at timed intervals. Although some of these tests are expensive, they are necessary for a definitive diagnosis. Sometimes an ultrasound examination may be required to eliminate the possibility of an adrenal tumour.

What are the treatment options?

1. Pituitary Tumour Treatment of the pituitary-dependant Cushing's Disease requires administration of tablets. A chemotherapy-type drug is used called Lysodren (Mitotane-OPPD). This is a human drug that has to be imported into the U.K. from the U.S.A. under special license. It is expensive, especially in the initial period, but as the dose is usually reduced to weekly or less treatments, the on-going costs are reduced. Lysodren destroys the abnormal adrenal tissue, thereby stopping the clinical signs. In order to achieve good results its use has to be carefully monitored. If not enough drug is used, the abnormal tissue persists and the disease continues; if too much is used, most or all of the adrenal cortex will be destroyed, which can be life-threatening. Because the pituitary is not being affected by the treatment, it continues to stimulate the adrenal gland. This means that continued treatment is necessary, with tablets given usually every 1 to 2 weeks. Although a cure is not achieved, control is possible for many years if the tumour is small. If the tumour is large, local effects of the tumour invading surrounding tissues in the head can be the limiting factor in survival.

2. Adrenal Tumour Treatment of an adrenal tumour requires major surgery. Although this surgery is not without risk, if it is successful and the tumour is not malignant, there is a good chance that the dog will regain normal health.

3. Iatrogenic Cushing's Disease Treatment of this form requires discontinuing the corticosteroids. This must be done in a controlled manner so that the body has time to resume production of the natural steroids that we all need everyday to function. If the administered corticosteroids are stopped too rapidly a life-threatening crisis may occur. If there have been any adverse effects on the adrenal glands, treatment will be needed to correct that problem.

Instructions for the treatment of Pituitary-dependent Cushings Disease

Treatment involves an initiating phase and a maintenance phase. The initiating phase arrests the disease and restores the dog to a more normal state. Some of the clinical signs, especially increased food and water intake, should stop within the first 1-3 weeks. Other signs, such as a poor hair coat or a bloated abdomen, may take several weeks or months to correct. The maintenance phase represents the phase of long-term therapy. This phase lasts the rest of the dog's life.

Food and water intake should be monitored. Both should return to a normal level. Normal water intake is approximately 60 ml/kg body weight per day. However water should not be restricted.

Initiating Phase
1. Your veterinary surgeon will have given you precise instructions regarding the medication and when it will be necessary to examine your dog again. However if any of the following occur, please contact your veterinary surgeon without delay.

a) water intake appears to drop dramatically
b) appetite drops dramatically
c) your dog does not eat a regular meal
d) if any vomiting or diarrhoea occurs
e) if the patient becomes unusually listless

2. If any of the above occur it may be necessary to perform a monitoring blood test (ACTH stimulation test). This test should be done early in the morning and will require your dog to be hospitalised for the day or part of the day. If the test is abnormal, the initiating phase will continue. If the test is normal, the maintenance phase will begin.

3. If any of the above signs occur, further or alternative medication may be instituted without delay. Follow the instructions given by the veterinary surgeon very carefully. If in any doubt at all, contact the practice. It is really important that there is close cooperation between owner and the veterinary surgeon at the beginning of any treatment for Cushing's Disease.

4. Report any other changes in your dog's behaviour that are out of the ordinary. The disease and treatment can result in abnormal behaviour. However, your dog can also have other diseases that occur concurrently but independently of Cushing's Disease. It is important that we differentiate between the two situations so that proper treatment can be taken.

5. Do not despair. Although a serious disease, many dogs with Cushing's Disease enjoy greatly improved quality of life for many years.

Following a successful initiating phase a ACTH Stimulation Test may be required to ascertain that normal cortisol levels have been reached. The results of this test help us to decide on a maintenance dose interval for the Lysodren.

Maintenance Phase
Once stabilised, medication will be administered approximately once every week or every fortnight (depending on the results of the ACTH Stimulation Test). Again follow your veterinary surgeon's instructions, particularly regarding progress or reports or attending check-ups. Further ACTH stimulation tests will be necessary about every 3-4 months to be sure that regulation is satisfactory.