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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, commonly known as cortisone. Either deficient production or excessive 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. Iatrogenic. Iatrogenic Cushing's Disease means that the excess of cortisone has resulted from excessive administration of cortisone. This may occur from oral or injectable medications over a long period.. Although the injections or tablets were given for a legitimate medical reason, their excess is now detrimental. Occasionally use of cortisone containing ointment over a long period of time can result in excessive intake due to absorption through the skin and to the dog licking.

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

3. Pituitary gland tumor. The most common cause of Cushing's Disease (85% of all cases) is a tumor of the pituitary gland. The tumor may be either benign or malignant. The tumor causes the pituitary to overproduce a hormone which stimulates the adrenal glands. Excessive cortisone secretion results. The tumor may be either microscopic or quite large. Depending on the size of the tumor, 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 tumor would give the patient a less favorable prognosis.

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 potbellied 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 are necessary to diagnose and confirm Cushing's Disease. Probably the most important one is the ACTH Stimulation Test. Other tests are 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.

What are the treatment options?

1. Iatrogenic Cushing's Disease: Treatment of this form requires a discontinuation of the cortisone that is being given. This must be done in a very controlled manner so that other consequences do not occur. Unfortunately, it usually results in a recurrence of the disease that was being treated by the cortisone. Because there may have been adverse effects on the adrenal glands, treatment is also needed to correct that problem.

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

3. Pituitary Tumor. Treatment of the pituitary-induced form of Cushing's Disease is the most complicated to treat. LysodrenÔ, (mitotane), not licensed for use in dogs in the UK, is the only drug that can be used to destroy the abnormal adrenal tissue. 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. Therefore, careful monitoring of the dog is necessary in order to achieve good results. Because the pituitary is not being affected by the treatment, it continues to stimulate the adrenal gland. This means that continued treatment is necessary, but this often only involves medication on a weekly or even longer basis. Although a cure is not achieved, control is possible for many years if the tumor is small. If the tumor is large, local effects of the tumor invading surrounding tissues in the head can be the limiting factor in survival.

Instructions for the treatment of the pituitary-induced form

Treatment of this form 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 (1 oz/lb) 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 diarrhea occurs

e. if the patient becomes unusually listless

2. If any of the above occur it may be necessary to repeat the blood test (ACTH stimulation test). This test should be done early in the morning and will require your dog to be hospitalized 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 your veterinary surgeon very carefully. If in any doubt at all, contact your practice. It is really important that there is close cooperation between owner and veterinary surgeon at the beginning of any treatment for Cushing's Disease.

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

Maintenance Phase

Once stabilized, medication will be administered approximately once every week or even 10 days. Again your veterinary surgeon's instructions, particularly regarding recalls or reports regarding progress must be strictly complied with. An ACTH stimulation test will be necessary about every 3-4 months to be sure that regulation is satisfactory. At the appropriate time, the specifics of the maintenance phase will be explained.

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