Use of low- and high-dose dexamethasone tests for distinguishing pituitary-dependent from adrenal tumor hyperadrenocorticism in dogs.
OBJECTIVE
To evaluate low- and high-dose dexamethasone suppression tests for differentiating pituitary dependent hyperadrenocorticism (PDH) from adrenal tumor hyperadrenocorticism (ATH) in dogs.


METHODS
Prospective study.


METHODS
181 dogs with PDH and 35 dogs with ATH.


METHODS
Plasma cortisol concentrations from dogs with naturally developing hyperadrenocorticism were evaluated before, and 4 and 8 hours after administration of standard low- and high-doses of dexamethasone (0.01 mg/kg of body weight, i.v., and 0.1 mg/kg, i.v.; respectively).


RESULTS
In response to the low-dose test, all but 3 dogs had an 8-hours post-dexamethasone plasma cortisol concentration that was consistent with a diagnosis of hyperadrenocorticism, that is, > or = 1.4 micrograms/dl. Criteria used to distinguish PDH from ATH in response to low-dose dexamethasone included a 4-hour post-dexamethasone plasma cortisol concentration < 50% of the basal value or < 1.4 micrograms/dl, or an 8-hours post-dexamethasone plasma cortisol concentration < 50% of the basal concentration. Criteria used to distinguish PDH from ATH in response to high-dose dexamethasone included 4- or 8-hour post-dexamethasone plasma cortisol concentrations < 50% of the basal concentration or < 1.4 micrograms/dl. In response to the low-dose test, 111 dogs met criteria for suppression (each had PDH). In response to the high-dose test, 137 dogs met criteria for suppression (2 had ATH, 135 had PDH). Twenty-six dogs with PDH (12%) had indications of adrenal suppression in response to high-dose but not low-dose testing.


CONCLUSIONS
Low-dose dexamethasone test has value as a discrimination test to distinguish dogs with PDH from those with ATH. The high-dose test need only be considered in dogs with hyperadrenocorticism that do not have adrenal suppression in response to the low-dose test.
Feldman
E C
EC
Department of Medicine, University of California, Davis 95616, USA.
Nelson
R W
RW
Feldman
M S
MS
D000306:Adrenal Cortex Neoplasms / Q000150:complications / Q000662:veterinary; D018246:Adrenocortical Adenoma / Q000150:complications / Q000662:veterinary; D018268:Adrenocortical Carcinoma / Q000150:complications / Q000662:veterinary; D000308:Adrenocortical Hyperfunction / Q000175:diagnosis / Q000209:etiology / Q000662:veterinary*; D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000818:Animals; D003907:Dexamethasone / Q000008:administration & dosage; D003937:Diagnosis, Differential; D004283:Dog Diseases / Q000175:diagnosis*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005938:Glucocorticoids / Q000008:administration & dosage; D006854:Hydrocortisone / Q000097:blood; D008279:Magnetic Resonance Imaging / Q000662:veterinary; D010911:Pituitary Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D011446:Prospective Studies; D014057:Tomography, X-Ray Computed / Q000662:veterinary
D005938:Glucocorticoids; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone