The adrenal gland of a dog can either underperform or overperform hormonally. The underperformance is called Addison’s disease, also known as hypoadrenocorticism. The opposite problem, characterized by overabundant adrenal cortisol production, is commonly known as Cushing’s disease, or hyperadrenocorticism.

Cushing’s disease is diagnosed in dogs as one of three clinical types:

Primary, or adrenal-based Cushing’s, meaning that the disease is a result of hypertrophy or a tumor of the adrenal gland’s cortex.

Secondary, or pituitary-dependent Cushing’s, meaning that the origin of the problem is from the pituitary gland, and it is an abnormality of the feedback to the adrenal glands.

Iatrogenic Cushing’s, meaning that drug therapy has induced the syndrome artificially.

Cushing’s disease commonly occurs in poodles, dachshunds, Boston terriers, boxers and beagles, but many other breeds have shown this clinical disorder. Either sex may be affected. Cushing’s usually affects middle-age dogs, but it has been documented in patients as young as 1 year.

Symptoms of Cushing’s disease include excessive urination, excessive water drinking, thin skin, hair loss, comedones on the skin and a pendulous (baggy) abdomen.

Veterinarians diagnose much of Cushing’s syndrome through a physical exam and a good patient history. Laboratory tests include a chemistry panel on the blood, which may reveal elevated levels of enzymes. Yet, the key tests in differentiating Cushing’s from many other hormonal diseases are the ACTH response test and the dexamethasone suppression tests. These are important since Cushing’s disease symptoms mimic diabetes mellitus, diabetes insipidus, hypothyroidism, kidney and liver diseases.

The ACTH response test shows how much cortisol may be produced by the adrenal glands by a calculated dose of outside (exogenous) ACTH administered by the veterinarian. The cortisol is measured both before and after the ACTH is given, and normal vs. abnormal adrenal glands can be measured by the results. Obviously, high cortisol responses to exogenous ACTH tell whether or not there is a problem with the cortisol production by the adrenal glands.

The dexamethasone suppression test shows whether or not the adrenal glands have the ability to bring their cortisol-producing levels down, once an outside dose of dexamethasone, a corticosteroid is administered by the vet. Suppression of the cortisol after the drug is given shows that the pituitary gland is serving its normal purpose. Failure to suppress shows an inability of the pituitary gland to perform, and therefore is the culprit in allowing for hormonal abnormality.