Evaluation of seasonal influences on adrenocorticotropic hormone response to the thyrotropin-releasing hormone stimulation test and its accuracy for diagnosis of pituitary pars intermedia dysfunction.
Abstract: Pituitary pars intermedia dysfunction (PPID) is an age-related neurodegenerative disorder, affecting >20 % of older horses. There is a need for improved endocrine tests for early disease detection, and the thyrotropin-releasing hormone (TRH) stimulation test has been recommended for diagnosis of early or mild cases. However, it is currently not recommended for year-round use due to marked seasonal variability. The aims of this cohort study were to evaluate effects of month and season on adrenocorticotropic hormone (ACTH) responses to TRH stimulation and to derive monthly cut-offs for PPID diagnosis. Sixty-three horses were assigned to control (n = 17), subclinical PPID (n = 21) and clinical PPID (n = 25) groups, based on a composite reference standard that combined clinical history and examination findings with endocrine test results. TRH stimulation tests were performed monthly for a 12-month period. Circannual changes were evaluated with one- and two-way repeated-measures analysis of variance and receiver operating characteristic curve analysis was used to derive cut-off values for basal and TRH-stimulated ACTH. TRH-stimulated ACTH concentrations were lowest in February-May and highest in August-October. Specificity of both basal and 30 min post-TRH ACTH was generally higher than sensitivity, and TRH stimulation had improved diagnostic accuracy compared to basal ACTH, although its sensitivity was not significantly greater year-round. TRH stimulation tests yielded considerably more positive results than basal ACTH in the subclinical group, but few additional positive results in clinical PPID cases. There were large differences between cut-offs that maximised sensitivity or specificity for TRH-stimulated ACTH, highlighting the importance of considering clinical presentation alongside test results in diagnostic decision-making.
Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.
Publication Date: 2023-10-05 PubMed ID: 37802466DOI: 10.1016/j.tvjl.2023.106035Google Scholar: Lookup
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Summary
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The research investigated the seasonal effects on how adrenocorticotropic hormone (ACTH) responds to thyrotropin-releasing hormone (TRH) stimulation test, and how this affects diagnosis of Pituitary pars intermedia dysfunction (PPID), a neurodegenerative disorder in horses, using the TRH test.
Background of the study
- More than 20% of older horses are affected by an age-related neurodegenerative disorder called Pituitary pars intermedia dysfunction (PPID).
- Currently, there is a need for improved endocrine tests to detect this disorder early on, with the Thyrotropin-Releasing Hormone (TRH) stimulation test recommended for diagnosing mild or early cases.
- The TRH stimulation test however is not recommended for year-round use because of its significant seasonal variability.
Purpose of the study
- The study sought to investigate the effects of month and season on the response of Adrenocorticotropic Hormone (ACTH) to TRH stimulation.
- Another objective was to define monthly cut-offs for diagnosing PPID.
- For this, the researchers created three groups of horses: control, subclinical PPID, and clinical PPID, which they arrived at by considering clinical history, examination findings, and endocrine test results.
Procedure and Findings
- A TRH stimulation test was administered to these horses monthly over a year’s period.
- The research found that ACTH concentrations triggered by TRH stimulation were lowest from February to May and highest from August to October.
- Generally, both basal and 30 min post-TRH ACTH had higher specificity than sensitivity, meaning it’s more effective at correctly identifying horses without PPID than identifying those with it.
- However, the TRH stimulation had improved diagnostic accuracy compared to basal ACTH, though its sensitivity was not significantly greater throughout the year.
Implications of the study
- The study suggests that TRH stimulation tests yielded more positive results than basal ACTH in the subclinical group but not much in the clinical PPID group.
- The large differences between the cut-offs that maximised sensitivity or specificity for TRH-stimulated ACTH underlined the importance of considering clinical presentation alongside test results in diagnostic decision-making.
Cite This Article
APA
Adams AA, Siard-Altman MH, Reedy SE, Barker D, Elzinga S, Sanz MG, Urschel K, Ireland JL.
(2023).
Evaluation of seasonal influences on adrenocorticotropic hormone response to the thyrotropin-releasing hormone stimulation test and its accuracy for diagnosis of pituitary pars intermedia dysfunction.
Vet J, 300-302, 106035.
https://doi.org/10.1016/j.tvjl.2023.106035 Publication
Researcher Affiliations
- Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA.
- Equine Studies, Department of Science & Health, Asbury University, One Macklem Drive, Wilmore, KY 40390, USA.
- Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA.
- Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA.
- Neurology Department, Michigan Medicine, University of Michigan, Ann Arbor, MI 48103, USA.
- Washington Animal Disease Diagnostic Laboratory, Washington State University,1940 SE Olympia Ave, Pullman, WA 99164-7034, USA.
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546-0215, USA.
- Institute of Infection, Veterinary and Ecological Sciences, Faculty of Health and Life Sciences, The University of Liverpool, Leahurst Campus, Neston, Cheshire CH64 7TE, UK. Electronic address: Joanne.Ireland@liverpool.ac.uk.
MeSH Terms
- Horses
- Animals
- Adrenocorticotropic Hormone / pharmacology
- Thyrotropin-Releasing Hormone / pharmacology
- Seasons
- Cohort Studies
- Pituitary Diseases / diagnosis
- Pituitary Diseases / veterinary
- Pituitary Gland, Intermediate / metabolism
- Horse Diseases / diagnosis
Conflict of Interest Statement
Conflict of interest None of the authors has any financial or personal relationships that could inappropriately influence or bias the content of the paper.
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