Hyperadrenocorticism (Cushing's disease, HAC)

Part 2 - Treatment Options

Treatment of HAC depends on whether we are dealing with a pituitary tumor (pituitary-dependent hyperadrenocorticism, or PDH) or an adrenal gland tumor.

Treatment for adrenal tumors

Adrenal tumors are first examined with ultrasound to determine which gland is the one with the tumor. Then the tumor is removed surgically. This is by no means a simple surgery. It is generally done at a surgical specialist, and there is intensive care monitoring after the adrenal gland is removed. This tumorous gland has been producing excessive amounts of cortisol for a long time. The opposite adrenal gland has completely shut down production, and will take up to several weeks to gear up production again. Until then, there is a high risk of complications associated with low adrenal hormone levels.

Treatment of pituitary-dependent hyperadrenocorticism (PDH)

Lifelong treatment is usually needed.

Mitotane (Lysodren)

This is a drug that selectively kills cells in the adrenal gland so that they cannot produce cortisol. The goal in treatment is to eliminate the clinical signs of Cushing's disease while avoiding side effects from the drug. The initial dosing regimen is designed to suppress cortisol production quickly, so Lysodren is given daily. After the initial period your pet will probably need the drug only once or twice a week.

It is very important that you monitor your pet's water consumption and appetite during treatment. You may need to be in daily contact with your veterinarian during this initial period. Inform your veterinarian immediately when your pet's water consumption drops or appetite decreases. At this time an ACTH stimulation test will be done. If the results are acceptable, a maintenance dosage will be instituted which is usually given once or twice a week rather than daily.

Selegiline (Anipryl)

This is a relatively new drug that was thought to have some benefits in the treatment of HAC. It changes the chemicals in the dog's brain. It can take up to 3 months before its full effects are noticed. Initial studies reported that about 25-75% of dogs are helped by Anipryl. Subsequent studies have failed to confirm this finding. The main effect it has is to alleviate the symptoms (mainly increased water consumption and urination) of the disease. There are no side effects with Anipryl. It can be expensive to give to larger dogs. Once started, if it is effective, it must be given for the rest of your pet's life to maintain the benefits.

Trilostane (Vetoryl)

Cortisol is an end product of progesterone metabolism. Trilostane inhibits progesterone production, and thereby decreases cortisol and decreases the side effects associated with high cortisol levels. 

Monitoring tests

Once Lysodren or Vetoryl have been started it may be necessary to repeat the ACTH stimulation test several times until the adrenal glands have stopped secreting cortisol. There will be at least two tests during the initial induction phase of treatment and one after the first 4 weeks of maintenance therapy. Thereafter, testing needs to be done every 3 to 4 months to ensure that the adrenal glands continue to be suppressed.

Anipryl does not require monitoring because it does not affect cortisol levels.

What to watch for at home

Keep track of (measure!) the amount of water your pet drinks per day and contact the clinic if the amount changes.

Contact the clinic immediately if your pet develops vomiting, diarrhea, weakness, decreased appetite, or lethargy. If you cannot bring your pet in to the clinic within 12-24 hours, administer prednisone as directed.