September 11, 2007 in Home

Cushing’s can sneak up on your dog

Carolyn Morrill, Dvm Correspondent
Associated Press photo

Cushing’s disease is more common in smaller dogs.
(Full-size photo)

Is your old dog drinking a lot of water and panting all the time? Does he have a thin coat? Maybe he is overweight with a potbelly. These signs are often dismissed as normal aging. However, they may actually be caused by a common disease in older dogs called “hyperadrenocorticism” or Cushing’s disease.

Cushing’s is caused by chronic exposure to cortisol, a hormone produced in the adrenal glands. Normally, cortisol is released from the adrenal glands in response to stress, such as running away from a predator. It gets the body geared up to burn energy quickly. Cortisol levels should drop back down to normal after the stressful event has passed.

With Cushing’s, however, the levels stay high, so the body is in a constant state of stress. Blood pressure and blood glucose levels are often higher than normal. The body is breaking down normal tissues for energy and redistributing fat to the abdomen. Muscles and ligaments weaken. The coat becomes thin, and skin lesions might appear. The dog eats and drinks more than normal. Excess cortisol also interferes with the immune system, so your dog may get infections more easily, such as urinary tract infections.

Although any dog can have the disease, it is more common in small dogs such as poodles, dachshunds and schnauzers. The average age at diagnosis is 12 years. Although cats can get Cushing’s too, it is relatively rare in them. Most cats (and some dogs) with Cushing’s will develop diabetes.

The signs of Cushing’s get worse so slowly and gradually that most dog owners don’t recognize them until they become severe. Common reasons for dogs to be brought to the vet are excessive thirst, urinating in the house, loss of hair to the point of baldness on the body, constant panting, profound weakness, or excessive appetite. (Both my dogs have excessive appetites too, but dogs with Cushing’s are so relentless in their quest for food that their behavior is alarming to their owners.) Dogs with this disease will exhibit some but not all of these signs.

What causes the excessive cortisol levels that lead to Cushing’s syndrome? Most of the time, it is caused by a benign tumor in the pituitary gland. This tumor produces a hormone called ACTH, which acts on the adrenal glands, causing them to continuously produce cortisol. Around 10 percent of Cushing’s cases are due to a tumor in one of the adrenal glands. The tumor cells produce cortisol constantly rather than only in response to stress.

Unfortunately, sometimes we cause Cushing’s disease in our dogs by giving them too many steroids. (Cortisol is a “steroid hormone,” but it isn’t the type of steroid that could make your dog a superathelete, banned for life from the Frisbee tournament.) Prednisone tablets, Depo-Medrol injections, and even topical steroids such as hydrocortisone sprays are basically just synthetic cortisol. They can create Cushing’s if they are overused, or if a dog is especially sensitive to them. This is called “iatrogenic” Cushing’s and can usually be treated just by withdrawing the offending drug.

Routine blood and urine tests will not diagnose the disease but can rule out other diseases. Dogs with Cushing’s usually have dilute urine and an increased liver enzyme called alkaline phosphatase. Special blood or urine tests are done to diagnose the disease, and an abdominal ultrasound is sometimes needed to see if an adrenal tumor is the cause.

It’s important to know which type of Cushing’s your dog has, because the treatments differ. Adrenal tumors should be surgically removed if possible, because successful surgery has the chance to cure the disease without the need for lifelong medications.

The pituitary form of the disease, which is far more common, is treated with medications. Your veterinarian will discuss treatment options with you. Each treatment has its pros and cons, and they can all have significant side effects. But, if Cushing’s is having a detrimental effect on your dog’s life, there are several treatments available that will help your dog regain her zest for life.

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