Causes of Cushing’s Disease
Cushing’s disease is caused by an excess of freely circulating corticosteroid hormones, which are produced by the adrenal glands. The adrenal glands are tiny, paired structures located in the abdomen above each kidney. The outer layer of these glands, called the adrenal cortex, produces corticosteroid hormones, which in turn are responsible for regulating electrolyte concentration, managing inflammatory reactions and suppressing the immune system, among other things. Production and release of steroid hormones are regulated by the pituitary gland, which is located in the brain. The pituitary gland produces adrenocorticotropic hormone (ACTH), which when released stimulates production of steroids by the adrenal glands.
The accurate term for Cushing’s disease is hyperadrenocorticism. It is most commonly caused by excess production and secretion of adrenocorticotropic hormone (ACTH) by the pituitary gland, due to either functional pituitary tumors or excess release of corticotrophin-releasing factor (CRF) by the hypothalamus. Cushing’s can also be caused by functional tumors of the adrenal gland, which promote excessive secretion of corticosteroids even without stimulation by pituitary ACTH. Finally, Cushing’s can be caused by excessive or prolonged use of steroid medications that stimulate or simulate excessive adrenal hormone production. This is called iatrogenic Cushing’s.
Unfortunately, other than managing the medical use of corticosteroids, there is no way to prevent hyperadrenocorticism in dogs. Functional tumors of the pituitary and/or adrenal glands occur for unknown reasons, and until the cause of those tumors is discovered, prevention of Cushing’s disease is not realistic.
Hyperadrenocorticism is a chronically progressive disease that can cause severe and eventually debilitating signs in domestic dogs. Fortunately, several medical protocols are available to help manage this disease.