Cushing's Disease in the Dog
a.k.a Hyperadrenocorticism
by Jennifer Fry, VMD

Disease Description:

Cushing's Disease or Hyperadrenocorticism is a disorder resulting from excessive circulating cortisol (a steroid). Cortisol in normal amounts is necessary for normal life; however, too much cortisol is detrimental. Most dogs that are affected are middle or old aged. The average dog is 10 years old and many breeds are affected. The most common signs of Cushing's Disease are increased appetite, increased thirst and urination, hair loss, lethargy, and pendulous abdomen (due to increased liver size and muscle breakdown). In most cases the cause of Cushing's Disease is due to a non-cancerous overgrowth (hyperplasia) of the pituitary gland (called Pituitary Dependent Hyperadrenocorticism or PDH). Cushing's disease can also be caused by a tumor in the adrenal glands, which are located in the abdomen next to the kidneys.

Cushing's disease is suspected in dogs with the classical clinical signs as well as an increased liver value noted on a routine chemistry blood panel. There are additional blood tests that must be performed to confirm diagnosis of Cushing's Disease. The three tests used are the ACTH Stimulation Test, Low Dose Dexamethasone Suppression (LDDS) Test and the High Dose Dexamethasone Suppression (HDDS) Test. One of the first two tests mentioned are used to diagnose Cushing's Disease and the last test may be used to differentiate whether Cushing's Disease is caused by an abnormal adrenal or pituitary gland.

Testing:

The ACTH Stimulation Test requires two blood samples. A blood sample is first taken to determine how much cortisol is in the blood. Then an injection of ACTH (cortisol stimulating hormone) is given to stimulate production of cortisol in the body and another blood sample is taken one hour later. Normal animals will produce a little cortisol while animals with Cushing's Disease will produce exaggerated amounts of cortisol. The LDDS and the HDDS tests are very similar to each other and only vary in the amount of dexamethasone (a steroid) given. A blood sample is first taken to determine how much cortisol is in the blood and then an injection of steroid is given to supress cortisol production. Two additional blood samples are taken at 4 and 8 hours after the injection. In normal animals, the body shuts down production on cortisol, but not in those affected with Cushing's Disease-they continue to produce cortisol.

Once your pet is diagnosed, your veterinarian will discuss with you the most appropriate course of treatment. Radiographs or an ultrasound of your pet may also be performed. The goal of treatment is to control the excessive secretion of cortisol by the pituitary or adrenal glands. Spontaneous remission of Cushing's disease does not occur and treatment is necessary. If your pet is not treated, his or her signs will not resolve and s/he will become ill and may suffer. Dogs with Cushing's disease are prone to respiratory, skin and bladder infections as well as developing life threatening blood clots, diabetes and heart disease. However, with the proper veterinary care your dog can lead a normal life.

Treatment:

Most patients are treated with a medication called Lysodren or Mitotane. Anipryl (Deprenyl) and Ketoconazole (Nizoral) are two other medications that may be used to treat Cushing's, but they generally are less effective than Lysodren therapy. If your pet has an adrenal tumor, the adrenal gland may be surgically removed (adrenalectomy) and/or treated with Lysodren.

Lysodren (a form of chemotherapy) destroys part of the adrenal glands, thus reducing the amount of cortisol in the blood. Your pet will receive a "loading" dose of this medication for several days after which a repeat ACTH Stimulation Test is performed (to monitor the drug's effects). Depending on the individual, some patients will be given prednisione (a steroid) during Lysodren treatment as well. If the cortisol level is sufficient, your pet will continue to receive the medication 2-3 times each week for life. In some cases the drug treatment "cures" the Cushing's Disease but then results in too little cortisol in the system (called hypoadrenocorticism or Addison's Disease). In these rare cases, your pet is supplemented with small doses steroids and does not need any more Lysodren.

At Home & Follow-Up Care:

Careful monitoring of your pet at home during this treatment is of utmost importance as well as frequent communication with your veterinarian. Recheck appointments and repeat blood testing are necessary to make sure your pet is receiving the proper dose of medication and ensure s/he stays healthy.

PLEASE CALL your VETERINARIAN IMMEDIATELY if your pet should develop anorexia, vomiting, diarrhea or lethargy while on Lysodren. If any of these symptoms are present, do NOT give any more Lysodren until you talk with the doctor. You may give prednisone as directed to help combat the anorexia and lethargy.

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