Use of endogenous ACTH concentration and adrenal ultrasonography to distinguish the cause of canine hyperadrenocorticism

Twenty-nine dogs were diagnosed with hyperadrenocorticism (HAC). A single d etermination of endogenous plasma adrenocorticotropic hormone (ACTH) and ad renal ultrasonography were used in a prospective study to differentiate bet ween pituitary-dependent HAC (PDH) and adrenal-dependent HAC (ADH). In 27 o ut of the 29 dogs (93 per cent), both endogenous plasma ACTH concentrations and adrenal ultrasonography indicated the same cause of HAC. Twenty-one of the 29 cases (72 per cent) were shown to be pituitary-dependent; all had p lasma ACTH concentrations of greater than 28 pg/ml (reference range 13 to 4 6 pg/ml) and both adrenal glands were ultrasonographically of similar size and of normal shape. All 21 cases responded well to mitotane therapy. Six c ases (21 per cent) were shown to be adrenal-dependent; all had plasma ACTH concentrations below the limit of the assay (<5 pg/ml) and the presence of an adrenal mass on ultrasonography. The sensitivity and specificity of adre nal ultrasonography and endogenous ACTH determinations to identify the caus e of HAC were demonstrated to be 100 per cent and 95 per cent, respectively , for ADH. These discriminatory tests are more accurate than published figu res for dexamethasone suppression testing.