Article #8

Cushing’s Disease In Dogs

Cushing's disease (or hyperadrenocorticism) strikes older dogs, and is often mistaken for the aging process itself. The victim loses hair, gains weight, loses bladder control and urinates in the house. Dog owners sometimes consider euthanizing dogs afflicted with Cushing's disease. But the disease is treatable.

Cushing's disease in dogs is characterized by chronic excessive cortisol hormone in the dog's system. Cortisol (cortisone-like) hormones are secreted by the dog's adrenal glands in response to chemical signals from the pituitary gland.

It's an important bodily regulator, governing reaction to stress, fat metabolism, kidney function, and important nerve and muscle functions. An oversupply of this hormone throws all these things out of balance, resulting in the symptoms of Cushing's disease.

There are several causes of Cushing's disease, of which the most common is a tiny (usually less than 3 millimeters in diameter) benign pituitary tumor, and the second most common is a tumor on the adrenal glands.

 

Cushing's Disease Testing

There are three different tests for Cushing's disease commonly used by veterinarians.

The most reliable test is the low dose dexamethasone suppression test, in which the dog is given a dose of dexamethasone (a cortisone-type drug) which, in a healthy animal, will signal the pituitary to stop the adrenal glands from secreting cortisol hormone. If the dog suffers from the pituitary-tumor type of Cushing's disease, the dexamethasone will not induce this response. Approximately 90% of dogs with Cushing's disease will test positive using this method.

The second type of test is called the ACTH stim test. This involves giving the dog a dose of adrenocorticotrophic hormone (ACTH), the hormone secreted by the pituitary gland that triggers the adrenal response. A high cortisol output two hours later indicates Cushing's disease. Although this test is less accurate than the dexamethasone test, it can be used for non-pituitary-tumor forms of the disease.

The third common test is a simple urine screening to test for cortisol concentration. A positive result of this test is not sufficient to diagnose Cushing's, but a negative result suffices to rule it out.
 

Treatment Of Cushing's Disease

Removing the cause of the condition (the tumor on the pituitary or adrenal glands) is seldom indicated in the case of an adrenal tumor and, given current surgical techniques, not an option in the case of a pituitary tumor. For this reason, Cushing's disease is normally treated with medication. There are four commonly-prescribed medications: Lysodren, Trilostane, Ketoconazole, and L-Deprenyl.

Lysodren is the oldest of these and is about equally effective for both pituitary and adrenal forms of the disease. However, Lysodren also has fairly severe side effects.

Trilostane is an alternative medication whose side effects are less severe than Lysodren, but similar in nature. L-Deprenyl is safer to prescribe, but only works with the pituitary form of the disease.
 

Veterinarians don't always recommend treatment of Cushing's disease. It depends on the age of the dog and on other medical conditions which may either make the drug treatments more dangerous or indicate a likely death from other causes. Also, the symptoms of Cushing's disease vary in severity, and milder forms of the disease may be judged not worth the risks involved in treating them.

The side effects of the drugs are particularly dangerous in animals with heart conditions, hypothyroidism, and diabetes, and at minimum these conditions need to be stabilized before beginning drug treatment for Cushing's disease.

Rare forms of Cushing's disease may result from the use of cortisone-type medications rather than from tumors on either the pituitary or the adrenal glands. In such cases, where it is medically possible, cessation of the medication or lowering of the dosage should eliminate the Cushing's symptoms within a month. However, this is not always possible, as the medication may be a treatment for a serious condition. For that reason, even in cases where medication is at fault, veterinarians sometimes continue the cortisone treatment and prescribe drug treatment for the Cushing's symptoms as well.