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Home / Equine Research Bank / J Vet Intern Med / Evaluation of the combined dexamethasone suppression/ thyrot...
Journal of veterinary internal medicine2006; 20(4); 987-993; doi: 10.1892/0891-6640(2006)20[987:eotcdt]2.0.co;2

Evaluation of the combined dexamethasone suppression/ thyrotropin-releasing hormone stimulation test for detection of pars intermedia pituitary adenomas in horses.

Abstract: 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. Objective: The sensitivity and specificity of the DEX/TRH test can be determined by comparing test results with histopathologic examination findings. Methods: 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: 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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Publication Date: 2006-09-08 PubMed ID: 16955827DOI: 10.1892/0891-6640(2006)20[987:eotcdt]2.0.co;2Google Scholar: Lookup
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  • Evaluation Study
  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This study investigated a combined dexamethasone suppression/thyrotropin-releasing hormone stimulation test (DEX/TRH test) as a method for detecting pars intermedia pituitary adenomas (PIPA) in horses. The researchers identified that the test had an 88% sensitivity rate, 76% specificity rate, and a high negative predictive value.

Methodology

  • The test was carried out on 42 horses of various breeds, aged between 2 and 33 years old.
  • The scientists measured plasma cortisol concentration before and 24 hours after the horses received an intravenous (IV) dose of dexamethasone (40 micrograms per kilogram of body weight).
  • They also measured the cortisol level before and 30 minutes after giving a 1 mg IV injection of thyrotrophin-releasing hormone (TRH), three hours after the dexamethasone injection.

Interpreting Test Results

  • If either the plasma cortisol concentration exceeded 10 nanograms per milliliter 24 hours after dexamethasone was administered, or if the change in cortisol concentration was 66% or more above the baseline 30 minutes after administering TRH, the DEX/TRH test results were deemed positive.
  • The diagnosis of PIPA was confirmed by histologic examination of the pituitary gland.

Findings and Conclusion

  • PIPA was detected in 17 out of 42 horses (40%) via histology.
  • The DEX/TRH test had sensitivities, specificity, positive predictive value (probability that positives are correctly identified), and negative predictive value (probability that negatives are correctly identified) of 88%, 76%, 71%, and 90% respectively.
  • The combined DEX/TRH test was found to be more sensitive than either of its components tested separately. It also had a high negative predictive value, suggesting its ability to accurately rule out horse without PIPA.
  • However, the combined test was not as specific as the TRH component alone (which had a specificity of 92%), indicating that the TRH test alone may have less false positives.
  • The research team concluded that the combined DEX/TRH test is a useful tool for screening older horses for PIPA.

Cite This Article

APA
Frank N, Andrews FM, Sommardahl CS, Eiler H, Rohrbach BW, Donnell RL. (2006). Evaluation of the combined dexamethasone suppression/ thyrotropin-releasing hormone stimulation test for detection of pars intermedia pituitary adenomas in horses. J Vet Intern Med, 20(4), 987-993. https://doi.org/10.1892/0891-6640(2006)20[987:eotcdt]2.0.co;2

Publication

Journal of veterinary internal medicine
ISSN: 0891-6640
NlmUniqueID: 8708660
Country: United States
Language: English
Volume: 20
Issue: 4
Pages: 987-993

Researcher Affiliations

Frank, Nicholas
  • Department of Large Animal Clinical Sciences, University of Tennessee, Knoxville 37996, USA. nfrank@utk.edu
Andrews, Frank M
    Sommardahl, Carla S
      Eiler, Hugo
        Rohrbach, Barton W
          Donnell, Robert L

            MeSH Terms

            • Animals
            • Dexamethasone
            • Female
            • Horse Diseases / diagnosis
            • Horses
            • Male
            • Pituitary Gland / pathology
            • Pituitary Neoplasms / diagnosis
            • Pituitary Neoplasms / veterinary
            • Sensitivity and Specificity
            • Thyroid Function Tests / veterinary
            • Thyrotropin-Releasing Hormone

            Citations

            This article has been cited 12 times.
            1. Stoeckle SD, Timmermann D, Merle R, Gehlen H. Plasma Amino Acids in Horses Suffering from Pituitary Pars Intermedia Dysfunction.. Animals (Basel) 2022 Nov 27;12(23).
              doi: 10.3390/ani12233315pubmed: 36496836google scholar: lookup
            2. Kirkwood NC, Hughes KJ, Stewart AJ. Prospective Case Series of Clinical Signs and Adrenocorticotrophin (ACTH) Concentrations in Seven Horses Transitioning to Pituitary Pars Intermedia Dysfunction (PPID).. Vet Sci 2022 Oct 17;9(10).
              doi: 10.3390/vetsci9100572pubmed: 36288186google scholar: lookup
            3. Kirkwood NC, Hughes KJ, Stewart AJ. Pituitary Pars Intermedia Dysfunction (PPID) in Horses.. Vet Sci 2022 Oct 10;9(10).
              doi: 10.3390/vetsci9100556pubmed: 36288169google scholar: lookup
            4. Nitzsche AM, Fey K, Büttner K, Gröf M, Staszyk C. The Gingiva of Horses With Pituitary Pars Intermedia Dysfunction: A Macroscopic Anatomical Evaluation.. Front Vet Sci 2021;8:786971.
              doi: 10.3389/fvets.2021.786971pubmed: 35146012google scholar: lookup
            5. Thane K, Uricchio C, Frank N. Effect of early or late blood sampling on thyrotropin releasing hormone stimulation test results in horses.. J Vet Intern Med 2022 Mar;36(2):770-777.
              doi: 10.1111/jvim.16362pubmed: 35049089google scholar: lookup
            6. Tsuchiya T, Noda R, Ikeda H, Maeda M, Sato F. Relationship between endogenous plasma adrenocorticotropic hormone concentration and reproductive performance in Thoroughbred broodmares.. J Vet Intern Med 2021 Jul;35(4):2002-2008.
              doi: 10.1111/jvim.16145pubmed: 34028083google scholar: lookup
            7. Tatum RC, McGowan CM, Dean RS, Ireland JL. Equine pituitary pars intermedia dysfunction: Identifying research priorities for diagnosis, treatment and prognosis through a priority setting partnership.. PLoS One 2021;16(1):e0244784.
              doi: 10.1371/journal.pone.0244784pubmed: 33395695google scholar: lookup
            8. Horn R, Stewart AJ, Jackson KV, Dryburgh EL, Medina-Torres CE, Bertin FR. Clinical implications of using adrenocorticotropic hormone diagnostic cutoffs or reference intervals to diagnose pituitary pars intermedia dysfunction in mature horses.. J Vet Intern Med 2021 Jan;35(1):560-570.
              doi: 10.1111/jvim.16017pubmed: 33368633google scholar: lookup
            9. Gehlen H, Schwarz B, Bartmann C, Gernhardt J, Stöckle SD. Pituitary Pars Intermedia Dysfunction and Metabolic Syndrome in Donkeys.. Animals (Basel) 2020 Dec 8;10(12).
              doi: 10.3390/ani10122335pubmed: 33302557google scholar: lookup
            10. Held F, Ekstrand C, Cvijovic M, Gabrielsson J, Jirstrand M. Modelling of oscillatory cortisol response in horses using a Bayesian population approach for evaluation of dexamethasone suppression test protocols.. J Pharmacokinet Pharmacodyn 2019 Feb;46(1):75-87.
              doi: 10.1007/s10928-018-09617-0pubmed: 30673914google scholar: lookup
            11. Spelta CW. Equine pituitary pars intermedia dysfunction: current perspectives on diagnosis and management.. Vet Med (Auckl) 2015;6:293-300.
              doi: 10.2147/VMRR.S74191pubmed: 30101114google scholar: lookup
            12. Carmalt JL, Waldner CL, Allen AL. Equine pituitary pars intermedia dysfunction: An international survey of veterinarians' approach to diagnosis, management, and estimated prevalence.. Can J Vet Res 2017 Oct;81(4):261-269.
              pubmed: 29081583
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