Statement from the Authors In preparing this document the Authors aimed to pool current information on canine and feline mast cell disease. The information was gathered from international studies and a emphasis was placed on material and opinion with a strong evidence base. We intend it to form the basis of our understanding in this disease at the current time and we anticipate that it will be particularly useful for the general practitioner. It should be emphasized that the authors are presenting this work from a European perspective.

The first part of the study aimed to describe prospectively the ultrasonographic features of the adrenal glands in 94 healthy cats and 51 chronically sick cats. It confirmed the feasibility of ultrasonography of adrenal glands in healthy and chronically sick cats, which were not statistically different. The typical hypoechoic appearance of the gland surrounded by hyperechoic fat made it recognisable. A sagittal plane of the gland, not in line with the aorta, may be necessary to obtain the largest adrenal measurements. The reference intervals of adrenal measurements were inferred from the values obtained in the healthy and chronically sick cats (mean ± 0.96 SD): adrenal length was 8.9-12.5 mm; cranial height was 3.0-4.8 mm; caudal height was 3.0-4.5 mm. The second part of the study consisted of a retrospective analysis of the ultrasonographic examination of the adrenal glands in cats with adrenal diseases (six had hyperaldosteronism and four had pituitary-dependent hyperadrenocorticism) and a descriptive comparison with the reference features obtained in the control groups from the prospective study. Cats with hyperaldosteronism presented with unilateral severely enlarged adrenal glands. However, a normal contralateral gland did not preclude a contralateral infiltration in benign or malignant adrenal neoplasms. The ultrasonographic appearance of the adrenal glands could not differentiate benign and malignant lesions. The ultrasonographic appearance of pituitary-dependent hyperadrenocorticism was mainly a symmetrical adrenal enlargement; however, a substantial number of cases were within the reference intervals of adrenal size.

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 5 28) or AIHAC (n 5 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 5.0 mm is an appropriate cut-off for AIHAC ultrasonographic diagnosis.

Background: Adrenocorticotropic hormone (ACTH) determination has been used for 30 years to distinguish ACTHdependent 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 (o5 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.