VP Client Information Sheets By VIN Community Contributors

Cushing's disease is a disorder of the adrenal glands in which excessive adrenal hormones are produced. The cause of hyperadrenalism (HAC) may be abnormal pituitary gland function, tumors of the adrenal gland, “cortisone” therapy or unexplained over-activity of the adrenal gland. Pituitary dependent HAC accounts for about 80% of all cases.

Hyperadrenalism is a slowly progressing disease and the early signs are often not noticed. These include increased appetite, increased drinking and urination, reduced activity, and enlargement of the abdomen. As the disease progresses, these signs intensify, and the pet may become fat, pant heavily, and lose hair evenly over each side of the body. In some cases, hair loss may be the only apparent change.

Extensive laboratory tests and radiographs or ultrasound may be needed to diagnose the condition, find its cause and plan treatment. Some animals respond to medical treatment alone, while others need both surgical and medical treatment. Unfortunately, some patients grow worse despite treatment.

Induction of Treatment for Cushing's Disease

1. Control, rather than cure, is the outcome of treatment in most cases of HAC. Treatment with mitotane must be carefully monitored, since the drugs used in therapy may cause underproduction of adrenal hormones and a shock-like state known as an Addisonian crisis. There is an alternative to mitotane called selegiline HCl (Anipryl). The benefits of this treatment are no worry of an Addisonian crisis as it does not destroy part of the adrenal gland. The drawbacks are it is expensive, especially for larger dogs, and has a variable success rate. Treatment with Anipryl consists of a pill once a day for life and includes regular monitoring of the disease through blood work.

2. Treatment is inducted with a drug called mitotane (Lysodren) You will be giving mitotane twice a day for 7 to 10 days (dosage will be determined by your veterinarian). Then an ACTH stimulation test is run to determine the response to treatment. The kidneys and electrolytes may be checked at this time also. Dogs with adrenal HAC may not respond as well to medical treatment alone as dogs with pituitary dependent HAC.

3. If your dog develops any of the following signs, contact your veterinarian immediately:

• Drinking less than ___ oz of water a day (2oz/kg) in dogs that were drinking excessive amounts (>3oz/kg/day) before treatment
• Vomiting or diarrhea
• Taking 15 to 30 minutes longer to eat than before start of mitotane therapy
• Listlessness, depression, or weakness
• Skin condition worsens

4. If adequate control is not reached after the first ACTH stimulation test then therapy will continue until a satisfactory ACTH stimulation test is obtained. The test is run about every 7 to 10 days.

Maintenance Therapy for Cushing's Disease

1. Once adequate control is reached then your dog will get mitotane twice a day once a week (dosage will be determined by your veterinarian).

2. An ACTH stimulation test will be run in 1 to 3 months after start of maintenance therapy and then every 3 to 6 months after that.

3. It is common for clinical signs to recur during maintenance therapy due to the dose becoming inadequate. If you notice signs returning see your veterinarian so the dose can be adjusted accordingly.

What to Expect

The average life expectancy for dogs with adrenal dependent HAC is 36 months. The average life expectancy for dogs with pituitary dependent HAC is approximately 30 months with younger dogs living longer (i.e., 4 years or more).

Many dogs ultimately die or are euthanized due to complications related to Cushing's disease such as pituitary macro tumor syndrome, pulmonary thromboembolism, diabetes mellitus, infection, etc.

1. Pituitary macro tumor syndrome is a result of the tumor on the pituitary gland expanding into other parts of the brain. The dog will begin showing neurologic signs such as aimless wandering, pacing, circling, and behavior alterations. These signs usually develop 6 months or more after diagnosis.

2. Pulmonary thromboembolism is most commonly seen shortly after treatment. The presenting sign is sudden respiratory distress or difficulty breathing. Once this occurs the prognosis for recovery is grave. It usually requires 7 to 10 days on oxygen therapy if the animal survives.

3. Development of diabetes mellitus is also another potential problem with Cushing's disease. The high levels of steroids in the blood stream can cause insulin resistance. The signs of diabetes are very similar to the signs of Cushing's disease, so it is important to notify your veterinarian if you notice them returning. Many dogs can have their diabetes controlled for a time with regular insulin therapy.

4. Infections are common in animals with Cushing's disease due to the overproduction of steroids. Steroids suppress the immune system and therefore prevent the animal from fighting off infection. One of the goals of treatment is to lower the animal's blood levels of steroids to prevent this from happening. Urinary tract infections and skin infections are most commonly seen. The more severe and life threatening ones include sepsis and pyelonephritis (kidney infection).

Date Published: 10/22/2004 1:08:00 PM