Hyperadrenocorticism or Cushing's syndrome refers to a disease state in which an overactive adrenal tissue produces excessive amounts of cortisone. Cortisone and related substances are essential hormones of the body, but when produced in excessive amounts these substances may cause systemic illness.

A small tumor in the pituitary gland (located at the base of the brain) is the cause of Cushing's syndrome in 80 to 85 percent of dogs with hyperadrenocorticism. The tumor produces a hormone called adrenocorticotropic hormone or ACTH that stimulates the adrenal glands to grow larger (become hyperplastic) and produce excessive amounts of cortisone. This type of Cushing's syndrome is called pituitary-dependent hyperadrenocorticism because it originates from the pituitary gland.

In the remaining 15 to 20 percent of dogs with Cushing's syndrome, the cause is a tumor of the adrenal gland. This form is called adrenal-dependent hyperadrenocorticism because it originates from the adrenal gland itself.

Occasionally, a dog might have a diagnosis of iatrogenic Cushing's disease. This is not an adrenal disorder, but rather it is caused by the administration of steroids (given to treat other diseases) to a dog. Long-term administration of steroids can cause a dog to exhibit all the classic signs of Cushing's disease. In this case, the excessive steroids are not being produced in the body, they are being provided as a form of medication to your pet.

Canine Cushing's syndrome usually occurs in middle-aged to older dogs with most affected dogs being over 9 years of age at presentation. The syndrome does not have a strong gender bias, but it may occur slightly more often in female dogs than in males. Dogs of any breed can develop Cushing's syndrome, but it is most common in poodles, dachshunds, miniature schnauzers, and German shepherds. Boxers and Boston terriers are prone to development of Cushing's syndrome caused by pituitary tumors.

Hyperadrenocorticism can be difficult to recognize due to its variable clinical symptoms and very gradual onset. For example, many owners mistakenly assume that the changes they see in their dog are simply a result of the aging process.

What to Watch For

Abnormal high blood concentration of cortisone results in the clinical symptoms of Cushing's syndrome. These include:

Increased water consumption (polydipsia)

Increased urinations (polyuria)

Increased appetite (polyphagia)

Abdominal distension (pot-bellied appearance)

Loss of hair on the trunk (alopecia)

Chronic skin or urinary tract infections, excessive panting, lethargy, muscle weakness, and calcium deposits in the skin (calcinosis cutis) are other symptoms of Cushing's syndrome.