Atypical Cushing’s Disease: Is It Really Atypical?

WHAT IS ATYPICAL CUSHING’S DISEASE? In 2002, clinical researchers from the UK described the first cases of what is often referred to as atypical Cushing’s disease (1). Dogs with atypical Cushing’s disease (ACD) have a history, physical examination findings, CBC, biochemical chemistry profile and urinalysis results, and adrenal imaging consistent with hyperadrenocorticism (HAC), however, routine screening tests (i.e., the low-dose dexamethasone suppression test (LDDST) and cortisol concentrations following the administration of ACTH (the ACTH response test) are normal. Yet, alternatively, one or more sex steroids are elevated (e.g., androstenedione, progesterone, or 17hydroxyprogesteone [17-OHP]) following administration of ACTH. The UK study evaluated 24 dogs with HAC; the cause of the HAC was not determined in 2 dogs. In the remaining 22 dogs, pituitary-dependent Cushing’s disease (PDH) was diagnosed in 16 dogs and 6 dogs had an adrenocortical tumor (AT). Of the 16 dogs with PDH, 3 dogs had ACD; of the 6 dogs with an AT, 4 dogs had ACD. All the dogs with ACD had elevated post-ACTH 17-OHP concentrations. In addition, all dogs in this study treated with standard therapeutic regimens of trilostane or mitotane showed resolution of clinical signs.