Open AccessEvaluation of the Combined Dexamethasone Suppression/Thyrotropin‐Releasing Hormone Stimulation Test for Detection of Pars Intermedia Pituitary Adenomas in Horses
Author(s) -
Frank Nicholas,
Andrews Frank M.,
Sommardahl Carla S.,
Eiler Hugo,
Rohrbach Barton W.,
Donnell Robert L.
Publication year - 2006
Publication title -
journal of veterinary internal medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.356
H-Index - 103
eISSN - 1939-1676
pISSN - 0891-6640
DOI - 10.1111/j.1939-1676.2006.tb01816.x
Subject(s) - medicine , endocrinology , dexamethasone , thyrotropin releasing hormone , trh stimulation test , stimulation , hormone , dexamethasone suppression test , pituitary adenoma , predictive value , pituitary gland , adenoma
Background : A combined dexamethasone (DEX) suppression/thyrotropin‐releasing hormone (TRH) test (DEX/TRH test) has been developed to evaluate horses for presence of a pars intermedia pituitary adenoma (PIPA), but to the authors' knowledge, the accuracy of this test has not been previously determined. Hypothesis : The sensitivity and specificity of the DEX/TRH test can be determined by comparing test results with histopathologic examination findings. Animals : Age of 42 horses of various breeds ranged from 2 to 33 years. Methods : Plasma cortisol concentration was measured before and 24 hours after IV administration of 40 μg of DEX/kg of body weight, and before and 30 minutes after IV administration of 1 mg of TRH that had been given 3 hours after the injection of DEX. Results of the DEX/TRH test were considered positive if either the plasma cortisol concentration exceeded 10 ng/mL 24 hours after DEX administration, or if the change in plasma cortisol concentration 30 minutes after injection of TRH was ≥66% above the 3‐hour baseline. Diagnosis of PIPA was determined by histologic examination of the pituitary gland. Results : PIPA was detected in 17 of 42 (40%) horses. The DEX/TRH test had sensitivity, specificity, positive predictive value, and negative (NPV) predictive value of 88, 76, 71, and 90%, respectively. Conclusions and Clinical Importance : The combined DEX/TRH test was more sensitive than either of its component tests and had a high NPV, but was not as specific as the TRH component alone (92%). The DEX/TRH test should be used to screen older horses for PIPA.