Evaluation of the combined dexamethasone suppression/ thyrotropin-releasing hormone stimulation test for detection of pars intermedia pituitary adenomas in horses |
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| Authors: | Frank Nicholas Andrews Frank M Sommardahl Carla S Eiler Hugo Rohrbach Barton W Donnell Robert L |
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| Institution: | Department of Large Animal Clinical Sciences, University of Tennessee, Knoxville 37996, USA. nfrank@utk.edu |
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| Abstract: | 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 microg 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 > or = 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. |
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| Keywords: | Equine Cushing's disease Hirsutism Hyperadrenocorticism Pituitary hyperplasia |
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