Stages of hyperadrenocorticism: response of hyperadrenocorticoid dogs to the combined dexamethasone suppression/ACTH stimulation test.

A study was designed to evaluate the response of blood cortisol content in dogs tentatively diagnosed as having hyperadrenocorticism by using the combined dexamethasone suppression/ACTH stimulation test procedure. Four groups of abnormal responses were identified in 54 dogs. In group I (14.8% of the dogs with abnormal responses), the only abnormality was partial suppression with dexamethasone (clinically normal dogs suppressed to less than 10 ng/ml). In group II (29.6%), 2 abnormalities were found: partial suppression with dexamethasone and hyperreactivity to the ACTH stimulation test. In group III (typical pituitary-dependent hypercortisolism, 48.1%), 3 abnormalities were found: base-line hypercortisolemia, partial suppression with dexamethasone, and hyperreactivity to the ACTH stimulation test. In group IV (7.4%), 2 abnormalities were found: base-line hypercortisolemia and partial suppression with dexamethasone. Base-line blood cortisol content was normal in 44.4% of the adrenopathic dogs. A normal response to ACTH stimulation was seen in 25.9% of the dogs, and 74.1% of the dogs hyperreacted to the ACTH stimulation test. All of the adrenopathic dogs were found to suppress partially with dexamethasone. Failure to suppress the adrenal gland completely (less than 10 ng/ml) with dexamethasone was the most consistent finding in adrenopathic dogs when using the combined dexamethasone suppression/ACTH stimulation test procedure. It was concluded that the test procedure is feasible, flexible, and convenient for clinical situations. Also, these results suggested that there may be several stages in the negative feedback failure associated with hyperadrenocorticism in dogs.