Hyperadrenocorticism (Cushings disease) in Dogs

Hyperadrenocorticism (Cushings) Disease is caused by an excessive production of cortisone by the adrenal gland This is a small gland just in front of the kidney. The adrenal gland is controlled by the pituitary gland, which sits just underneath the brain. Cushings disease can be caused by a small tumour in either of these glands. Usually the tumour is in the pituitary gland, and cannot be removed. The tumours mostly behave in a benign fashion. That is they don’t keep growing, but they do release hormones that cause problems.

Cushings disease can occur at any age but is most common in dogs over 6 years of age. The disease may be more common in German Shepherds, Toy poodles, Daschunds, and terriers than other breeds, Though dogs of any breed and sex can be affected.

The excess cortisone produced affects lots of different parts of the body. Dogs that have been treated for long periods, with large amounts of cortisone can also exhibit these signs.

About 10% of dogs with Cushings disease will have Diabetes at the same time.

Clinical signs
The clinical signs of Cushings often come on slowly over months or years. Things you may notice are:

• Increased water consumption ( over 100mls/kg of body weight is considered abnormal)
• Increased urination
• Increased appetite
• Poor hair coat often with bald patches.
• Change in skin colour ( often becomes darker)
• A pot bellied appearance
• Lethargy
• Panting
• Obesity
• Heat intolerance
• Acne
• Failure to breed
• Weakness
• Elevated blood pressure
• Hard (calcified) lumps in the skin

Very few dogs exhibit all of these signs.

Diagnosis
Cushings disease is often suspected based on clinical signs, or after routine blood screening. Cushings is one of the most common causes of liver disease. Initially we will suspect Cushings disease based on your history, clinical examination and lab results.

Specific blood screening is required to confirm the diagnosis. This is quite simply but may take a few hours to perform. Most commonly a test called an ‘ACTH stimulation test’ (takes about 2hours) or a ‘low dose dexamethasone suppression test’ (takes about 8 hours) will be performed. An abdominal ultrasound or xray may also be performed to evaluate the liver and adrenal glands.

Up to 20% of dogs with Cushings will have normal test results. In this case we may need to repeat the tests in a few weeks, if no other cause of your pets problems are found.

Treatment
Occasionally with the adrenal form of Cushings disease, surgery can be performed by specialists and may be curative. In this case the affected gland is removed. However it carries a high degree of risk and hence medical management is generally the preferred option.

This is done using tablets. There are a number of treatment options, each of which has some advantages, and disadvantages. We will discuss the best option for you and your pet. Regardless of which option we use, your pet will require ongoing tablets for the rest of their life. We will also periodically need to do some blood tests every 3-6 months to check the treatment is working properly.

Dependant on the drug used,these are given at varying intervals from once or twice a day, to a weekly dose.

The two main drugs that are used currently are Trilostane, that is given once or twice daily, and Mitotane that is usually given either once or twice weekly. They both work in suppressing cortisol production by their effects on the adrenal cortex. Due to its more rapid onset of action, and less chance of side effects Trilostane is rapidly becoming the drug of choice.

However both drugs carry the risks of side effects if not monitored closely, so regular function testing of the adrenal gland (ACTH function tests) every 3-6 months , is highly recommended.

*Feldman & Nelson. 1996 “ Canine and Feline Endocrinology and Reproduction” second ed. WB Saunders and Co New York