Diagnosis of Hyperadrenocorticism Cushing's Syndrome in Dogs: Which Tests Are Best

CAUSES
The most common cause of Cushing’s syndrome in dogs is iatrogenic. Glucocorticoids are used in treating many conditions. The anti-inflammatory and immune-
suppressive effects of glucocorticoids in dogs can be dramatic. However, not only
are these beneficial effects common, but dogs demonstrate their sensitivity to this
class of hormone by consistently exhibiting a number of progressive, sometimes alarming, clinical signs. These same clinical signs are common in naturally occurring hyperadrenocorticism in dogs, in whom about 85% have pituitary dependent hyperadrenocorticism (PDH) and the remaining 15% have a solitary functioning adrenocortical tumor (FAT). Dogs with PDH have an autonomously functioning, ACTH-secreting, adenoma. Chronic excess ACTH secretion leads to excess circulating glucocorticoids and bilateral adrenocortical hyperplasia. Cortisol-secreting adrenocortical tumors are usually soliary, can be either an adenoma or carcinoma, but in either case, the tumor autonomously secretes excessive quantities of glucocorticoids. Other causes for Cushing’s syndrome have been recognized and are rare. In all cases, the final common denominator is the chronic and excessive exposure of dogs to glucocorticoids that causes signs, physical changes, laboratory test abnormalities, and need for imaging. Iatrogenic Cushing’s is easily treated: stop giving the drug. Naturally occurring Cushing’s is a more complicated diagnosis and treatment is never inexpensive nor is it ever without risk. These notes focus on the naturally occurring syndromes. […]