Cushing’s Syndrome in Dogs

Cushing’s syndrome is caused by the excess presence of glucocorticoids in the dog’s body.  Glucocorticoids are substances produced by the adrenal glands on top of the kidneys to control inflammation and suppress the immune system.  In addition, almost all types of steroids given to dogs are glucocorticoids.  Thus, Cushing’s syndrome can be caused by either the body producing excess glucocorticoids or the administration of steroids for another illness in the dog.

There are two reasons the dog’s body might produce excess glucocorticoids.  The first is a malfunction of the pituitary gland as it produces the hormone that tells the adrenal gland to produce glucocorticoids.  The pituitary gland produces too much hormone, so the adrenal gland makes more glucocorticoids than is healthy for the dog.  This is the most common cause of Cushing’s syndrome accounting for eighty-five percent of cases.

In fifteen percent of cases, the overproduction of glucocorticoids is caused by a tumor in the adrenal glands.  This is treated by removing the tumor from the adrenal glands.  As long as the tumor has not spread, the outlook for the dog is good.  If, however, the tumor has spread the outcome can be poor.

Cushing’s usually occurs in dogs six years and older.  Some breeds, such as Poodles, Boston Terriers, Dachshunds, and Boxers, are more likely to have his problem than other breeds.

The symptoms of Cushing’s syndrome are varied because glucocorticoids effect so many parts of the body.  The dog may lose his hair on his body, but usually not his head or legs.   His skin will darken where he has lost his hair.   The hair that does remain is dry and dull.  The dog may have small blackheads on his abdomen.  In addition, the abdomen is distended, giving the dog a pot-bellied look.  The dog may also exhibit lethargy with reduced activity, infertility in females, infertility in males due to testicular atrophy, loss of muscle mass, and weakness.  The dog may drink excessively and have to urinate excessively.  Cushing’s can kill a dog if not treated.

Cushing’s is diagnosed based on these symptoms and laboratory tests.  These tests measure serum cortisol in the blood before and after the injection of ACTH and dexamethasone.  In addition, CT scans and magnetic resonance imaging can be used to see small tumors on either the pituitary gland or the adrenal glands.  Ultrasound can be used to make sure the adrenal glands are the same size and that one doesn’t have a tumor on it.

Cushing’s due to the pituitary gland telling the adrenals to produce too much glucocorticoids is treated with a drug that suppresses the production of glucocorticoids.  It is a drug that requires close monitoring to make sure the dog is not getting too much glucocorticoids but is not getting to little, either.

The average lifespan of a dog with Cushing’s disease is two years with treatment.  Some dogs do live considerably longer, however.  If the Cushing’s is due to the administration of chronic steroids, reducing the amount of steroids given can alleviate the Cushing’s and extend the dog’s life.