the gland scheme of things: cushing's disease

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Older dog | Senior Beagle with Cushing's Disease
Posted by Dr. Kim Smyth on May 24 2011

Cortisol is a hormone produced by the adrenal gland, which sits next to the kidney. Cortisol is also stored in the adrenal gland, and is released in response to stress to help our bodies cope. By mobilizing fat and sugar stores, it ensures that we are ready for a "fight or flight" situation. We all need cortisol to live, but two endocrine diseases relating to cortisol can affect the way cortisol is made. In Cushing’s disease and Addison’s disease, too much or too little cortisol is made.

Causes of Cushing's disease

There are two causes of Cushing's disease, both related to cortisol levels in the body.

The way a "hyper" child has too much energy, a pet affected with hyperadrenocorticism, or Cushing’s disease, has too much cortisol. This can be for one of two reasons:

1. Pituitary-dependent Cushing’s disease

2. Adrenal-dependent Cushing’s disease

Pituitary-dependent 

The pituitary gland is located at the base of the brain and is in charge of telling the adrenal gland to make the hormone cortisol. Most cases of Cushing’s disease are due to a small tumor in the pituitary gland. This tumor secretes too much of the hormone that tells the adrenal gland to make cortisol, therefore, the adrenal gland makes too much cortisol.

Adrenal-dependent 

In about 15% of the cases of Cushing's disease, the problem lies in the adrenal gland itself. A tumor in one or both adrenal glands will lead to overproduction of cortisol.

Cushing's disease symptoms

In both types of Cushing's disease, too much cortisol is released. You may be familiar with the side effects of steroids if your pet has been on a short course of them before. Increased thirst, increased appetite and urinary accidents can all occur with exposure to steroids. Long term exposure to steroids, like that which occurs in Cushing's, leads to muscle wasting, so you will see muscle weakness and a pot-bellied appearance.

Changes in the skin and an increase in skin infections also occurs with Cushing’s disease. Most owners come in with the problem of a dog that is ravenous at all times and drinking the water bowl dry.

How it's diagnosed

Some findings in routine blood work can arouse suspicion of Cushing's disease, and from there, further blood work will need to be done. Usually, your veterinarian will run one or more timed blood tests, and will probably need to perform an abdominal ultrasound to visualize the adrenal glands. The tests needed to diagnose Cushing’s disease may seem excessive, but it is important to determine whether the illness is due to a tumor in the pituitary gland or a tumor in the adrenal gland.

Having pet insurance that covers chronic illnesses and also the exam fees (regardless of whether a diagnosis is made), such as Petplan, can make sure your pet receives all the diagnostics necessary to determine the cause of his health problems.

How it's treated

Treatment of Cushing's depends on the cause. Animals with pituitary-dependent Cushing’s disease can be treated medically with one of two medications.

Historically, a drug called Lysodren was used to control excess control of cortisol by eroding part of the adrenal gland. A newer drug called Trilostane is becoming the treatment of choice for most veterinarians, because it controls the production of cortisol without eroding the adrenal gland. Both drugs require periodic blood tests to ensure proper cortisol levels are reached.

If your pet has adrenal-dependent Cushing’s disease, additional testing will be done to determine if the tumor is malignant (cancerous) or benign. Surgery can be performed to remove the affected adrenal gland. Sometimes the drug Lysodrencan be used in higher doses to help control cortisol production.

If your pet has symptoms of Cushing's disease, it's time for a visit to your veterinarian. Other diseases can produce similar symptoms, so your vet will probably start with routine blood work. If Cushing's disease is diagnosed, you and your veterinarian can sit down together and discuss the treatment options that will be best for your pet.

Updated October 24, 2019