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Background: Adrenal ultrasonography (US) in dogs with hyperadrenocorticism (HAC) is commonly used to distinguish adrenocorticotropic hormone (ACTH)-independent (AIHAC) and ACTH-dependent hyperadrenocorticism (ADHAC). To date, no cut-off values for defining adrenal atrophy in cases of adrenal asymmetry have been determined. Given that asymmetrical hyperplasia is sometimes observed in ADHAC, adrenal asymmetry without ultrasonographic proof of adrenocortical tumor such as vascular invasion or metastasis can be equivocal. Objective: The purpose of this study was to compare adrenal US findings between cases of ADHAC and AIHAC in dogs with equivocal adrenal asymmetry (EAA), and to identify useful criteria for their distinction. Animals: Forty dogs with EAA were included. Methods: Ultrasound reports of HAC dogs with adrenal asymmetry without obvious vascular invasion or metastases were reviewed. Dogs were classified as cases of ADHAC (n = 28) or AIHAC (n = 19), determined by plasma ACTH concentration. The thickness, shape, and echogenicity of both adrenal glands and presence of adjacent vascular compression were compared between AIHAC and ADHAC groups. Results: The maximal dorsoventral thickness of the smaller gland (SDV) ranged from 2.0 to 5.0 mm in AIHAC and from 5.0 to 15.0 mm in ADHAC. The 95% confidence intervals for estimated sensitivity and specificity of a SDV cut-off set at 5.0 mm in the diagnosis of AIHAC were 82-100 and 82-99%, respectively. Other tested US criteria were found to overlap extensively between the 2 groups, precluding their usefulness for distinction. Conclusion and Clinical Importance: In EAA cases, an SDV less than 5.0 mm is an appropriate cut-off for AIHAC ultrasonographic diagnosis.

Abstract Background Adrenocorticotropic hormone (ACTH) determination has been used for 30 years to distinguish ACTH-dependent hyperadrenocorticism (ADHAC) from ACTH-independent hyperadrenocorticism (AIHAC) in dogs. However, the few studies that have evaluated its diagnostic accuracy, based in the majority of cases on older assays, have been associated with systematic, but highly variable proportions of misclassified or unclassified cases. Objective The purpose of the present study is to evaluate the accuracy of a validated ACTH immunoluminometric assay (ILMA) for differentiating between ADHAC and AIHAC. Animals One hundred and nine dogs with hyperadrenocorticism were included: 91 with ADHAC and 18 with AIHAC. Methods Retrospective study. Dogs displaying feedback inhibition after the dexamethasone suppression test, adrenal symmetry, or both were considered to have ADHAC. AIHAC was demonstrated by adrenal tumor histology. For each group, ACTH determination by ILMA was reviewed. Results In the ADHAC group, plasma ACTH measurements ranged between 6 and 1250 pg/mL (median, 30 pg/mL). In the AIHAC group, all ACTH concentrations were below the lower quantification limit of the assay (<5 pg/mL). The 95% confidence interval was 85–100% for sensitivity and 97–100% for specificity in AIHAC diagnosis. Conclusion and Clinical Importance No overlap in ACTH concentrations was observed between dogs with ADHAC and dogs with AIHAC. The use of a new technique with high analytical sensitivity made it possible to use a low threshold (5 pg/mL), avoiding the misclassification of some ADHAC cases with low, but quantifiable concentrations of ACTH. The assessment of ACTH concentrations by ILMA is an accurate tool for differentiating between ADHAC and AIHAC.

Background: The measurement of adrenal gland size on computed tomography (CT) scan has been proposed for the etiological diagnosis of hyperadrenocorticism (HAC) in dogs. Symmetric adrenal glands are considered to provide evidence for ACTH‐dependent hyperadrenocorticism (ADHAC), whereas asymmetry suggests ACTH‐independent hyperadrenocorticism (AIHAC). However, there are currently no validated criteria for such differentiation. Objective: The aim of this retrospective study was to compare various adrenal CT scan measurements and the derived ratios in ADHAC and AIHAC cases, and to validate criteria for distinguishing between these conditions in a large cohort of dogs. Animals: Sixty‐four dogs with HAC (46 ADHAC, 18 AIHAC). Methods: Dogs with confirmed HAC and unequivocal characterization of its origin were included. Linear measurements of adrenal glands were made on both cross‐sectional and reformatted images. Results: An overlap was systematically observed between the AIHAC and ADHAC groups for all measurements tested. Overlaps also were observed for ratios tested. For the maximum adrenal diameter ratio derived from reformatted images (rADR), only 1/18 AIHAC dogs had a rADR within the range for ADHAC. For a threshold of 2.08, the 95% confidence intervals for estimated sensitivity and specificity extended from 0.815 to 1.000 and from 0.885 to 0.999, respectively, for AIHAC diagnosis. Conclusion and Clinical Importance: Measurements from cross‐sectional or reformatted CT scans are of little use for determining the origin of HAC. However, rADR appears to distinguish accurately between ADHAC and AIHAC, with a rADR > 2.08 highly suggestive of AIHAC.

Background Diagnosis of pituitary‐dependent hyperadrenocorticism (PDH) in cats is challenging because there is no specific diagnostic test. Hypothesis/Objective The determination of plasma ACTH precursor (POMC and pro‐ACTH) concentration might facilitate the diagnosis of PDH in cats. The aim of the study was to evaluate prospectively the plasma concentrations of ACTH precursors in a small cohort of cats with PDH and to estimate the value of this approach for diagnosis. Animals Four groups of cats were included: group 1 (cats with PDH), group 2 (cats with diabetes mellitus but not hyperadrenocorticism (HAC)), group 3 (cats with diabetes mellitus and confirmed acromegaly but not HAC), and group 4 (healthy cats). Methods PDH diagnosis was based on clinical data, low‐dose dexamethasone suppression test (LDDST), and adrenal and pituitary gland computed tomography (CT) scan. For groups 2, 3, and 4, hyperadrenocorticism was excluded by LDDST or urine cortisol:creatinine ratio (UCCR). An immunoluminometric assay was used to determine plasma concentrations of ACTH precursors in the 4 groups of cats. Results Group 1 contained 9 cats (enlarged pituitary gland in 7/9). Plasma ACTH precursor concentrations ranged from <53 to >1010 pmol/L with 8/9 concentrations ≥229 pmol/L. Groups 2, 3, and 4 included 13, 7, and 13 cats, respectively. Plasma ACTH precursor concentrations ranged from <53 to 96 pmol/L in group 2, <53 to 72 pmol/L in group 3, and <53 to 99 pmol/L in group 4. Conclusion and Clinical Importance High plasma concentration of ACTH precursors in cats (>100 pmol/L) is highly suggestive of PDH.

It is difficult to predict the size of pituitary corticotroph tumors in dogs with Cushing's disease (pituitary-dependent hyperadrenocorticism [PDH]) without pituitary imaging techniques. The purpose of this study was to examine the relationship between plasma adrenocorticotropin hormone (ACTH) precursor concentration and pituitary size in dogs with Cushing's disease. Plasma concentrations of ACTH precursors (pro-opiomelanocortin [POMC]/pro-ACTH) and pituitary tumor height/brain area were measured in 36 dogs with pituitary corticotroph adenomas of various sizes. There was a correlation between tumor size (measured as the pituitary tumor height/brain area ratio [P/B]) and POMC/pro-ACTH concentration (r = .70; P < .0001). Dogs with P/B > or = 0.40 x 10(-2) mm(-1) had higher concentrations of ACTH precursors than dogs with P/B < 0.40 x 10(-2) mm(-1) (median concentration 85 pmol/L, range 15-1,350 pmol/L, n = 14 versus 15 pmol/L, range 15-108 pmol/L, n = 22; P < .0001). With a threshold of 35 pmol/L of POMC/pro-ACTH concentration, the estimated sensitivity and specificity of the kit were 93% (95% confidence interval [CI], 79-100%) and 86% (95% CI, 73-100%), respectively. We interpret these data as indicating that measurement of POMC and pro-ACTH might be of value in the characterization of tumor size in dogs with Cushing's disease. Low POMC/pro-ACTH concentrations make it unlikely that a large pituitary tumor exists in dogs with PDH.It is difficult to predict the size of pituitary corticotroph tumors in dogs with Cushing's disease (pituitary-dependent hyperadrenocorticism [PDH]) without pituitary imaging techniques. The purpose of this study was to examine the relationship between plasma adrenocorticotropin hormone (ACTH) precursor concentration and pituitary size in dogs with Cushing's disease. Plasma concentrations of ACTH precursors (pro-opiomelanocortin [POMC]/pro-ACTH) and pituitary tumor height/brain area were measured in 36 dogs with pituitary corticotroph adenomas of various sizes. There was a correlation between tumor size (measured as the pituitary tumor height/brain area ratio [P/B]) and POMC/pro-ACTH concentration (r = .70; P < .0001). Dogs with P/B > or = 0.40 x 10(-2) mm(-1) had higher concentrations of ACTH precursors than dogs with P/B < 0.40 x 10(-2) mm(-1) (median concentration 85 pmol/L, range 15-1,350 pmol/L, n = 14 versus 15 pmol/L, range 15-108 pmol/L, n = 22; P < .0001). With a threshold of 35 pmol/L of POMC/pro-ACTH concentration, the estimated sensitivity and specificity of the kit were 93% (95% confidence interval [CI], 79-100%) and 86% (95% CI, 73-100%), respectively. We interpret these data as indicating that measurement of POMC and pro-ACTH might be of value in the characterization of tumor size in dogs with Cushing's disease. Low POMC/pro-ACTH concentrations make it unlikely that a large pituitary tumor exists in dogs with PDH.

It is difficult to predict the size of pituitary corticotroph tumors in dogs with Cushing's disease (pituitary‐dependent hyperadrenocorticism [PDH]) without pituitary imaging techniques. The purpose of this study was to examine the relationship between plasma adrenocorticotropin hormone (ACTH) precursor concentration and pituitary size in dogs with Cushing's disease. Plasma concentrations of ACTH precursors (pro‐opiomelanocortin [POMC]/pro‐ACTH) and pituitary tumor height/brain area were measured in 36 dogs with pituitary corticotroph adenomas of various sizes. There was a correlation between tumor size (measured as the pituitary tumor height/brain area ratio [P/B]) and POMC/pro‐ACTH concentration (r= .70; P< .0001). Dogs with P/B < 0.40 × 10‐2 mm‐1 had higher concentrations of ACTH precursors than dogs with P/B < 0.40 × 10‐2 mm‐1 (median concentration 85 pmol/L, range 15‐1,350 pmol/L, n = 14 versus 15 pmol/L, range 15–108 pmol/L, n = 22; P < .0001). With a threshold of 35 pmol/L of POMC/pro‐ACTH concentration, the estimated sensitivity and specificity of the kit were 93% (95% confidence interval [CI], 79–100%) and 86% (95% CI, 73–100%), respectively. We interpret these data as indicating that measurement of POMC and pro‐ACTH might be of value in the characterization of tumor size in dogs with Cushing's disease. Low POMC/pro‐ACTH concentrations make it unlikely that a large pituitary tumor exists in dogs with PDH.