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McGowan C, Ireland J, Carslake H. Diagnosis of equine endocrine disease special issue. Vet J 2024; 306:106177. [PMID: 38880228 DOI: 10.1016/j.tvjl.2024.106177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2024] [Accepted: 06/13/2024] [Indexed: 06/18/2024]
Affiliation(s)
- Catherine McGowan
- Department of Equine Clinical Science, The University of Liverpool, Leahurst CH64 7TE, UK
| | - Joanne Ireland
- Department of Equine Clinical Science, The University of Liverpool, Leahurst CH64 7TE, UK.
| | - Harry Carslake
- Department of Equine Clinical Science, The University of Liverpool, Leahurst CH64 7TE, UK
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Viviani P, Lavado RA, Chavarria NH, Ragno VM, Montgomery JB. Spring and fall blood concentrations of adrenocorticotropic hormone, insulin, and thyroxine in healthy horses in Saskatchewan. THE CANADIAN VETERINARY JOURNAL = LA REVUE VETERINAIRE CANADIENNE 2024; 65:335-342. [PMID: 38562984 PMCID: PMC10945457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Objective To characterize concentrations of adrenocorticotropic hormone (ACTH), insulin, and thyroxine (T4) at 2 times of the year in healthy horses in Saskatchewan. Animals and procedure A prospective, observational study was carried out in 52 healthy, client-owned horses. Inclusion criteria were no recent travel outside of Saskatchewan, normal physical examination findings, and no history or evidence of ongoing illness. Blood concentrations of ACTH, insulin and T4 were determined by chemiluminescence. Samples were collected in spring and fall and compared using the paired Student's t-test or Wilcoxon signed-rank test. Generalized estimating equations were used to assess the associations between ACTH, T4, and insulin concentrations and gender, age, season, body condition score, glucose concentration, and breed. Results There were increases in both ACTH and insulin concentrations in the fall compared to spring (P < 0.001 and P = 0.001, respectively). Other than season, insulin concentration was associated with breed, whereas ACTH concentration was associated with age. Finally, T4 concentration was associated with breed and glucose concentration, but not with season. Conclusion and clinical relevance These results highlighted the differences between spring and fall concentrations of both ACTH and insulin in healthy horses residing in the Canadian prairie provinces, which are known for extreme differences in summer and winter temperatures as well as day length. Geographically adjusted reference values are necessary to account for these variations, to improve diagnostic accuracy. This is the first published Canadian study evaluating these factors and their associations with hormone concentrations in clinically healthy animals.
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Affiliation(s)
- Paula Viviani
- Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan S7N 5B4 (Viviani, Lavado, Chavarria, Ragno, Montgomery); University of São Paulo, 87 Av. Prof. Orlando Marques de Paiva, São Paulo 05508-900, Brazil (Lavado)
| | - Ronaldo Avella Lavado
- Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan S7N 5B4 (Viviani, Lavado, Chavarria, Ragno, Montgomery); University of São Paulo, 87 Av. Prof. Orlando Marques de Paiva, São Paulo 05508-900, Brazil (Lavado)
| | - Nora H Chavarria
- Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan S7N 5B4 (Viviani, Lavado, Chavarria, Ragno, Montgomery); University of São Paulo, 87 Av. Prof. Orlando Marques de Paiva, São Paulo 05508-900, Brazil (Lavado)
| | - Valentina M Ragno
- Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan S7N 5B4 (Viviani, Lavado, Chavarria, Ragno, Montgomery); University of São Paulo, 87 Av. Prof. Orlando Marques de Paiva, São Paulo 05508-900, Brazil (Lavado)
| | - Julia B Montgomery
- Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan S7N 5B4 (Viviani, Lavado, Chavarria, Ragno, Montgomery); University of São Paulo, 87 Av. Prof. Orlando Marques de Paiva, São Paulo 05508-900, Brazil (Lavado)
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Ireland JL, Lester A, Banse HE. Factors affecting measurement of basal adrenocorticotropic hormone in adult domestic equids: A scoping review. Vet J 2024; 304:106071. [PMID: 38341024 DOI: 10.1016/j.tvjl.2024.106071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Revised: 01/12/2024] [Accepted: 02/01/2024] [Indexed: 02/12/2024]
Abstract
Measurement of basal adrenocorticotropic hormone (ACTH) concentration is the most commonly used diagnostic test for pituitary pars intermedia dysfunction (PPID). Although several pre-analytical and analytical factors have been reported to affect basal ACTH concentrations in equids, the extent to which these have been evaluated in the context of PPID diagnosis is unclear. The objectives of this scoping review were to identify and systematically chart current evidence about pre-analytical and analytical factors affecting basal ACTH concentrations in adult domestic equids. Systematic searches of electronic databases and conference proceedings were undertaken in June 2022, repeated in October 2022 and updated in August 2023. English language publications published prior to these dates were included. Screening and data extraction were undertaken individually by the authors, using predefined criteria and a modified scoping review data extraction template. After removal of duplicates, 903 publications were identified, of which 235 abstracts were screened for eligibility and 134 publications met inclusion criteria. Time of year, exercise, breed/type and transportation were the factors most frequently associated with significant increases in ACTH concentration (n = 26, 16, 13 and 10 publications, respectively). Only 25 publications reported inclusion of PPID cases in the study population, therefore the relationship between many factors affecting basal ACTH concentration and diagnostic accuracy for PPID remains undefined. However, several factors were identified that could impact interpretation of basal ACTH results. Findings also highlight the need for detailed reporting of pre-analytical and analytical conditions in future research to facilitate translation of evidence to practice.
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Affiliation(s)
- J L Ireland
- Department of Equine Clinical Science, Faculty of Health and Life Sciences, The University of Liverpool, Leahurst CH64 7TE, Cheshire, UK.
| | - A Lester
- Department of Equine Clinical Science, Faculty of Health and Life Sciences, The University of Liverpool, Leahurst CH64 7TE, Cheshire, UK
| | - H E Banse
- School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA
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Menzies-Gow NJ, Banse HE, Duff A, Hart N, Ireland JL, Knowles EJ, McFarlane D, Rendle D. BEVA primary care clinical guidelines: Diagnosis and management of equine pituitary pars intermedia dysfunction. Equine Vet J 2024; 56:220-242. [PMID: 37795557 DOI: 10.1111/evj.14009] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Accepted: 08/19/2023] [Indexed: 10/06/2023]
Abstract
BACKGROUND Pituitary pars intermedia dysfunction (PPID) is a prevalent, age-related chronic disorder in equids. Diagnosis of PPID can be challenging because of its broad spectrum of clinical presentations and disparate published diagnostic criteria, and there are limited available treatment options. OBJECTIVES To develop evidence-based primary care guidelines for the diagnosis and treatment of equine PPID based on the available literature. STUDY DESIGN Evidence-based clinical guideline using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework. METHODS Research questions were proposed by a panel of veterinarians and developed into PICO or another structured format. VetSRev and Veterinary Evidence were searched for evidence summaries, and systematic searches of the NCBI PubMed and CAB Direct databases were conducted using keyword searches in July 2022 and updated in January 2023. The evidence was evaluated using the GRADE framework. RESULTS AND RECOMMENDATIONS The research questions were categorised into four areas: (A) Case selection for diagnostic testing, pre-test probability and diagnostic test accuracy, (B) interpretation of test results, (C) pharmacological treatments and other treatment/management options and (D) monitoring treated cases. Relevant veterinary publications were identified and assessed using the GRADE criteria. The results were developed into recommendations: (A) Case selection for diagnostic testing and diagnostic test accuracy: (i) The prevalence of PPID in equids aged ≥15 years is between 21% and 27%; (ii) hypertrichosis or delayed/incomplete hair coat shedding provides a high index of clinical suspicion for PPID; (iii) the combination of clinical signs and age informs the index of clinical suspicion prior to diagnostic testing; (iv) estimated pre-test probability of PPID should be considered in interpretation of diagnostic test results; (v) pre-test probability of PPID is low in equids aged <10 years; (vi) both pre-test probability of disease and season of testing have strong influence on the ability to diagnose PPID using basal adrenocorticotropic hormone (ACTH) or ACTH after thyrotropin-releasing hormone (TRH) stimulation. The overall diagnostic accuracy of basal ACTH concentrations for diagnosing PPID ranged between 88% and 92% in the autumn and 70% and 86% in the non-autumn, depending on the pre-test probability. Based on a single study, the overall diagnostic accuracy of ACTH concentrations in response to TRH after 30 minutes for diagnosing PPID ranged between 92% and 98% in the autumn and 90% and 94% in the non-autumn, depending on the pre-test probability. Thus, it should be remembered that the risk of a false positive result increases in situations where there is a low pre-test probability, which could mean that treatment is initiated for PPID without checking for a more likely alternative diagnosis. This could compromise horse welfare due to the commencement of lifelong therapy and/or failing to identify and treat an alternative potentially life-threatening condition. (B) Interpretation of diagnostic tests: (i) There is a significant effect of breed on plasma ACTH concentration, particularly in the autumn with markedly higher ACTH concentrations in some but not all 'thrifty' breeds; (ii) basal and/or post-TRH ACTH concentrations may also be affected by latitude/location, diet/feeding, coat colour, critical illness and trailer transport; (iii) mild pain is unlikely to have a large effect on basal ACTH, but caution may be required for more severe pain; (iv) determining diagnostic thresholds that allow for all possible contributory factors is not practical; therefore, the use of equivocal ranges is supported; (v) dynamic insulin testing and TRH stimulation testing may be combined, but TRH stimulation testing should not immediately follow an oral sugar test; (vi) equids with PPID and hyperinsulinaemia appear to be at higher risk of laminitis, but ACTH is not an independent predictor of laminitis risk. (C) Pharmacologic treatments and other treatment/management options: (i) Pergolide improves most clinical signs associated with PPID in the majority of affected animals; (ii) Pergolide treatment lowers basal ACTH concentrations and improves the ACTH response to TRH in many animals, but measures of insulin dysregulation (ID) are not altered in most cases; (iii) chasteberry has no effect on ACTH concentrations and there is no benefit to adding chasteberry to pergolide therapy; (iv) combination of cyproheptadine with pergolide is not superior to pergolide alone; (v) there is no evidence that pergolide has adverse cardiac effects in horses; (vi) Pergolide does not affect insulin sensitivity. (D) Monitoring pergolide-treated cases: (i) Hormone assays provide a crude indication of pituitary control in response to pergolide therapy, however it is unknown whether monitoring of ACTH concentrations and titrating of pergolide doses accordingly is associated with improved endocrinological or clinical outcome; (ii) it is unknown whether monitoring the ACTH response to TRH or clinical signs is associated with an improved outcome; (iii) there is very weak evidence to suggest that increasing pergolide dose in autumn months may be beneficial; (iv) there is little advantage in waiting for more than a month to perform follow-up endocrine testing following initiation of pergolide therapy; there may be merit in performing repeat tests sooner; (v) timing of sampling in relation to pergolide dosing does not confound measurement of ACTH concentration; (vi) there is no evidence that making changes after interpretation of ACTH concentrations measured at certain times of the year is associated with improved outcomes; (vii) evidence is very limited, however, compliance with PPID treatment appears to be poor and it is unclear whether this influences clinical outcome; (viii) evidence is very limited, but horses with clinical signs of PPID are likely to shed more nematode eggs than horses without clinical signs of PPID; it is unclear whether this results in an increased risk of parasitic disease or whether there is a need for more frequent assessment of faecal worm egg counts. MAIN LIMITATIONS Limited relevant publications in the veterinary scientific literature. CONCLUSIONS These findings should be used to inform decision-making in equine primary care practice.
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Affiliation(s)
| | - Heidi E Banse
- School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA
| | - Aimi Duff
- Rainbow Equine Hospital, North Yorkshire, UK
| | | | - Joanne L Ireland
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Wirral, UK
| | | | - Dianne McFarlane
- College of Veterinary Medicine, University of Florida, Gainesville, Florida, USA
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Vorster DM, Wang W, Kemp KL, Bamford NJ, Bertin FR. Clinical implications of imprecise sampling time for 10- and 30-min thyrotropin-releasing hormone stimulation tests in horses. Equine Vet J 2024; 56:291-298. [PMID: 37649416 DOI: 10.1111/evj.13991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 08/08/2023] [Indexed: 09/01/2023]
Abstract
BACKGROUND The thyrotropin-releasing hormone (TRH) stimulation test is used to diagnose pituitary pars intermedia dysfunction (PPID) using 10- or 30-min protocols. Imprecise sampling time for the 10-min protocol can lead to misdiagnoses. OBJECTIVES To determine the effect of imprecise sampling time for the 30-min protocol of the TRH stimulation test. STUDY DESIGN In vivo experiment. METHODS Plasma immunoreactive adrenocorticotropin (ACTH) concentrations were measured 9, 10, 11, 29, 30 and 31 min after intravenous administration of 1 mg of TRH in 15 control and 12 PPID horses. Differences in ACTH concentrations between sampling times, variability in ACTH concentrations between protocols, and diagnostic classification of PPID were assessed using Friedman's test, Bland-Altman plots, and Fisher's exact test, respectively, with 95% confidence intervals reported and significance set at p < 0.05. RESULTS Imprecise sampling time resulted in variable ACTH concentrations, but significant differences in absolute ACTH concentrations were not detected for imprecise sampling within each protocol or between protocols. Imprecise sampling changed PPID diagnostic classification for 3/27 (11 [4-28] %) horses for both protocols. Using the 30-min protocol as a reference, 1/12 (8 [1-35] %) horses returned a negative test result and 5/12 (42 [19-68] %) horses returned equivocal test results that would be considered positive in practice due to the presence of supportive clinical signs. MAIN LIMITATIONS Limited sample size and inter-horse variability reduced the ability to detect small but potentially relevant differences. CONCLUSIONS Overall, the impact of imprecise sampling was not significantly different between the 10- and 30-min TRH stimulation test protocols. However, diagnostic classification for PPID would have varied between the 10- and 30-min protocols in this population, if clinical signs had been ignored. Precise timing during TRH stimulation tests and contextual interpretation of ACTH concentrations remain fundamental for the diagnosis of PPID.
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Affiliation(s)
- Dante M Vorster
- Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Wenqing Wang
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
| | - Kate L Kemp
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
| | - Nicholas J Bamford
- Melbourne Veterinary School, The University of Melbourne, Parkville, Victoria, Australia
| | - François-René Bertin
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
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Bertin FR, Frank N, Breuhaus BA, Schott HC, Kritchevsky JE. Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals. Equine Vet J 2024; 56:243-252. [PMID: 37533378 DOI: 10.1111/evj.13981] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Accepted: 07/13/2023] [Indexed: 08/04/2023]
Abstract
Equine thyroid disorders pose a diagnostic challenge in clinical practice because of the effects of nonthyroidal factors on the hypothalamic-pituitary-thyroid axis, and the horse's ability to tolerate wide fluctuations in thyroid hormone concentrations and survive without a thyroid gland. While benign thyroid tumours are common in older horses, other disorders like primary hypothyroidism or hyperthyroidism in adult horses and congenital hypothyroidism in foals are rare. There is a common misunderstanding regarding hypothyroidism in adult horses, especially when associated with the clinical profile of obesity, lethargy, and poor performance observed in dogs and humans. Low blood thyroid hormone concentrations are often detected in horses as a secondary response to metabolic and disease states, including with the nonthyroidal illness syndrome; however, it is important to note that low thyroid hormone concentrations in these cases do not necessarily indicate hypothyroidism. Assessing equine thyroid function involves measuring thyroid hormone concentrations, including total and free fractions of thyroxine (T4) and triiodothyronine (T3); however, interpreting these results can be challenging due to the pulsatile secretion of thyroid hormones and the many factors that can affect their concentrations. Dynamic testing, such as the thyrotropin-releasing hormone stimulation test, can help assess the thyroid gland response to stimulation. Although true hypothyroidism is extremely rare, thyroid hormone supplementation is commonly used in equine practice to help manage obesity and poor performance. This review focuses on thyroid gland pathophysiology in adult horses and foals, interpretation of blood thyroid hormone concentrations, and evaluation of horses with thyroid disorders. It also discusses the use of T4 supplementation in equine practice.
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Affiliation(s)
- François-René Bertin
- School of Veterinary Science at The University of Queensland, UQ Gatton Campus, Gatton, Queensland, Australia
| | - Nicholas Frank
- College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA
| | - Babetta A Breuhaus
- College of Veterinary Medicine at North Caroline State University, Raleigh, North Carolina, USA
| | - Harold C Schott
- College of Veterinary Medicine at Michigan State University, East Lansing, Michigan, USA
| | - Janice E Kritchevsky
- College of Veterinary Medicine at Purdue University, West Lafayette, Indiana, USA
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Drozdzewska K, Winter J, Barton AK, Merle R, Gehlen H. Influence of feeding and other factors on adrenocorticotropin concentration and thyrotropin-releasing hormone stimulation test in horses and ponies. Equine Vet J 2024; 56:342-351. [PMID: 38010866 DOI: 10.1111/evj.14030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 10/31/2023] [Indexed: 11/29/2023]
Abstract
BACKGROUND The basal (bACTH) and post-thyrotropin-releasing hormone stimulation concentration of adrenocorticotropin (pACTH) are recommended for diagnosis of pituitary pars intermedia dysfunction (PPID). Many factors influence bACTH (e.g., disease, age, month) and some affect the results only in autumn (e.g., breed, colour, sex). There are discrepancies about the impact of feeding on b/pACTH. OBJECTIVES To determine whether feeding, month, age, breed, colour, sex and body condition score affect b/pACTH. STUDY DESIGN Prospective crossover. METHODS Sixty-one animals were divided into groups: healthy, PPID, treated-PPID. The b/pACTH was measured three times (1 mg protirelin; blood collection after 10 min; mid-November to mid-July) after different feedings: fasting, hay, hay + grain. Friedman's test was applied to evaluate the influence of feeding on b/pACTH and linear mixed model to evaluate impact of further factors. RESULTS The b/pACTH was not significantly affected by feeding (p = 0.7/0.5). The bACTH was lowest in healthy (29.3 pg/mL, CI 9-49.5 pg/mL) and highest in PPID-group (58.9 pg/mL, CI 39.7-78.1 pg/mL). The pACTH was significantly lower in healthy (396.7 pg/mL, CI 283.2-510.1 pg/mL) compared to PPID (588.4 pg/mL, CI 480.7-696.2 pg/mL) and treated-PPID group (683.1 pg/mL, CI 585.9-780.4 pg/mL), highest in July (881.2 pg/mL, CI 626.3-1136.3 pg/mL) and higher in grey (723.5 pg/mL, CI 577.5-869.4 pg/mL) than other colours (338.7 pg/mL, CI 324.8-452.5 pg/mL). The size of effect for those variables was >0.5. MAIN LIMITATIONS Small number of animals, subsequent bACTH measurements were significantly lower in each horse. CONCLUSIONS There was no evidence that feeding influences the b/pACTH. There was evidence that pergolide affects the bACTH but it had little effect on pACTH. Further investigation of the impact of month and coat colour on b/pACTH is warranted to better interpret the results.
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Affiliation(s)
| | | | | | - Roswitha Merle
- Institute of Veterinary Epidemiology and Biostatistics, Freie Universität Berlin, Berlin, Germany
| | - Heidrun Gehlen
- Equine Clinic, Freie Universität Berlin, Berlin, Germany
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Li FI, Spence RJ, de Laat MA, Harris PA, Sonntag J, Menzies-Gow NJ, Durham AE, Bailey SR, Sillence MN. Association between insulin dysregulation and adrenocorticotropic hormone in aged horses and ponies with no clinical signs of pituitary pars intermedia dysfunction. Equine Vet J 2023; 55:1003-1011. [PMID: 36641787 DOI: 10.1111/evj.13925] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 01/05/2023] [Indexed: 01/16/2023]
Abstract
BACKGROUND High concentrations of adrenocorticotropic hormone (ACTH) are used as an indicator of pituitary pars intermedia dysfunction (PPID), but other factors that may influence ACTH need to be understood, if diagnostic reference ranges for ACTH are to be used with confidence. Insulin dysregulation (ID) could be one such factor, as insulin affects pituitary hormones in other species. OBJECTIVES To test the hypothesis that a relationship exists between high insulin and high ACTH in aged (>15-year-old) animals with no clinical signs of PPID. STUDY DESIGN A cohort study. METHODS Thirteen horses and eleven ponies (17-25 years-old; mares and geldings) were clinically examined for signs of PPID in the spring (November 2020) and autumn (April 2021). On the same day, blood samples were taken before and 2 h after an oral glucose test (OGT). Concentrations of insulin, glucose, ACTH and cortisol were measured. RESULTS There was no association between ACTH and cortisol. However, there was a positive linear correlation between ACTH and post-OGT (insulin in the autumn (r = 0.427, p = 0.04). Two horses and six ponies had ACTH above the cut-off value for PPID diagnosis, and of these eight animals, six also had insulin concentrations above the cut-off value for ID. MAIN LIMITATIONS The cohort was small and thyrotropin-releasing hormone (TRH) stimulation tests were not performed. CONCLUSIONS In autumn, high ACTH was associated with ID, when no clinical signs of PPID were present. Because ACTH is used in PPID diagnosis, further work is required to understand this interaction.
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Affiliation(s)
- Fang I Li
- School of Biology & Environmental Science, Science Faculty, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Robert J Spence
- School of Biology & Environmental Science, Science Faculty, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Melody A de Laat
- School of Biology & Environmental Science, Science Faculty, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Patricia A Harris
- Equine Studies Group, Waltham Petcare Science Institute, Leicestershire, UK
| | - Johanna Sonntag
- Boehringer Ingelheim Vetmedica GmbH, Ingelheim am Rhein, Germany
| | | | | | - Simon R Bailey
- Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - Martin N Sillence
- School of Biology & Environmental Science, Science Faculty, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
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Adams AA, Siard-Altman MH, Reedy SE, Barker D, Elzinga S, Sanz MG, Urschel K, Ireland JL. 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 2023; 300-302:106035. [PMID: 37802466 DOI: 10.1016/j.tvjl.2023.106035] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2023] [Revised: 09/26/2023] [Accepted: 10/03/2023] [Indexed: 10/10/2023]
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.
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Affiliation(s)
- A A Adams
- Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA
| | - M H Siard-Altman
- Equine Studies, Department of Science & Health, Asbury University, One Macklem Drive, Wilmore, KY 40390, USA
| | - S E Reedy
- Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA
| | - D Barker
- Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA
| | - S Elzinga
- Neurology Department, Michigan Medicine, University of Michigan, Ann Arbor, MI 48103, USA
| | - M G Sanz
- Washington Animal Disease Diagnostic Laboratory, Washington State University,1940 SE Olympia Ave, Pullman, WA 99164-7034, USA
| | - K Urschel
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546-0215, USA
| | - J L Ireland
- Institute of Infection, Veterinary and Ecological Sciences, Faculty of Health and Life Sciences, The University of Liverpool, Leahurst Campus, Neston, Cheshire CH64 7TE, UK.
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Stewart AJ, Ireland JL, Durham AE, McGowan CM. Diagnosis of equine pituitary pars intermedia dysfunction. Vet J 2023; 300-302:106036. [PMID: 37805159 DOI: 10.1016/j.tvjl.2023.106036] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 09/25/2023] [Accepted: 10/04/2023] [Indexed: 10/09/2023]
Abstract
Equine pituitary pars intermedia dysfunction (PPID) is common in aged horses. The majority of horses respond well to treatment, but treatment is lifelong, meaning accurate diagnosis of PPID is important. Similar to any condition, there is no perfect laboratory test to diagnose PPID and accuracy is affected by the characteristics of the population in which the test is being evaluated. This review details the importance of consideration of clinical factors and diagnostic test accuracy. Basal adrenocorticotrophic hormone (ACTH) concentration is used most frequently in practice and has very good diagnostic accuracy when used in combination with clinical judgement and the correct application of diagnostic thresholds. The thyrotropin-releasing hormone stimulation test can be used in horses with equivocal test results following basal ACTH testing, or to evaluate subtle cases due to its improved accuracy.
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Affiliation(s)
| | - Joanne L Ireland
- School of Veterinary Science, Faculty of Health and Life Sciences, The University of Liverpool, Neston CH64 7TE, UK
| | - Andy E Durham
- Liphook Equine Hospital, Liphook, Hampshire GU30 7JG, UK
| | - Catherine M McGowan
- School of Veterinary Science, Faculty of Health and Life Sciences, The University of Liverpool, Neston CH64 7TE, UK.
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Ireland J, McGowan C. Deciphering reference intervals and clinical decision limits in equine endocrine diagnostic testing. Vet J 2023; 300-302:106037. [PMID: 37832629 DOI: 10.1016/j.tvjl.2023.106037] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 10/05/2023] [Accepted: 10/10/2023] [Indexed: 10/15/2023]
Abstract
Reference intervals (RIs) and clinical decision limits (CDLs) are frequently established to facilitate interpretation of values of endocrine biomarkers in the diagnosis of disease. Despite their commonplace use in clinical decision-making, these concepts can be confused. Comparing a test result with a RI provides an estimation as to whether or not the individual is healthy, whereas comparison with a CDL facilitates identification of individuals with a particular disease state or at greater risk of adverse clinical outcomes. In practice, there will also be a range of results for which the discriminative ability of the test is insufficient to inform a specific diagnostic decision. Including a range of uncertain test results, or 'grey zone', between positive and negative avoids the constraint of a binary decision in classifying an individual with a test value above (or below) a single cut-off value as diseased. This review will detail the application of both RIs and CDLs, including defining the range of uncertain test results, in the context of equine endocrinology.
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Affiliation(s)
- Joanne Ireland
- Department of Equine Clinical Science, Faculty of Health and Life Sciences, The University of Liverpool, Leahurst, CH64 7TE Cheshire, UK.
| | - Catherine McGowan
- Department of Equine Clinical Science, Faculty of Health and Life Sciences, The University of Liverpool, Leahurst, CH64 7TE Cheshire, UK
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12
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Clark BL, Stewart AJ, Kemp KL, Bamford NJ, Bertin FR. Evaluation of field-testing protocols to diagnose insulin dysregulation in ponies using a Bayesian approach. Vet J 2023; 298-299:106019. [PMID: 37536451 DOI: 10.1016/j.tvjl.2023.106019] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2022] [Revised: 07/23/2023] [Accepted: 07/31/2023] [Indexed: 08/05/2023]
Abstract
Field tests and their association with laminitis have not been evaluated in large cohorts. The objectives of this study were to evaluate the performance of basal insulin (BI), the oral sugar test (OST) and the insulin tolerance test (ITT) to diagnose ID and investigate their association with laminitis. Insulin dysregulation status was determined in 146 ponies using BI (insulin concentration >20 µIU/mL), an OST (insulin concentration >65 µIU/mL at 60 or 90 min after oral administration of 0.45 mL/kg corn syrup) and an ITT (< 50% reduction in glucose concentration 30 min after intravenous administration of 0.1 IU/kg insulin). Laminitis was identified using modified-Obel scores. A Bayesian approach was used to define the characteristics of the tests and receiver operating characteristic curves were used to assess their association with laminitis. All tests were well tolerated and laminitis was diagnosed in 9% of ponies. Insulin dysregulation was diagnosed in 15% of ponies using BI, 38% using the OST and 54% using the ITT with 11% of ponies positive for all three tests. The sensitivities and specificities of BI, the OST and the ITT to diagnose ID were 0.52 (95% confidence interval [CI], 0.35-0.79) and 0.97 (95% CI, 0.91 - 1.00), 0.84 (95% CI, 0.70 - 0.94) and 0.60 (95% CI, 0.49 - 0.71), and 0.85 (95% CI, 0.68-0.96) and 0.88 (95% CI, 0.75 - 0.97), respectively. Only BI and the OST were associated with laminitis (P = 0.003 and 0.015, respectively).
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Affiliation(s)
- B L Clark
- The University of Queensland, 5391 Warrego Hwy, Gatton, QLD 4343, Australia.
| | - A J Stewart
- The University of Queensland, 5391 Warrego Hwy, Gatton, QLD 4343, Australia
| | - K L Kemp
- The University of Queensland, 5391 Warrego Hwy, Gatton, QLD 4343, Australia
| | - N J Bamford
- The University of Melbourne, Park Drive, Parkville, VIC 3010, Australia
| | - F-R Bertin
- The University of Queensland, 5391 Warrego Hwy, Gatton, QLD 4343, Australia
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13
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Bamford NJ, Stewart AJ, El-Hage CM, Bertin FR, Bailey SR. Investigation of breed differences in plasma adrenocorticotropic hormone concentrations among healthy horses and ponies. Vet J 2023; 296-297:105995. [PMID: 37207985 DOI: 10.1016/j.tvjl.2023.105995] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Revised: 04/06/2023] [Accepted: 05/16/2023] [Indexed: 05/21/2023]
Abstract
Plasma adrenocorticotropic hormone (ACTH) concentration is commonly measured to diagnose pituitary pars intermedia dysfunction (PPID). Several intrinsic and extrinsic factors affect ACTH concentrations, including breed. The objective of this study was to prospectively compare plasma ACTH concentrations among different breeds of mature horses and ponies. Three breed groups comprised Thoroughbred horses (n = 127), Shetland ponies (n = 131) and ponies of non-Shetland breeds (n = 141). Enrolled animals did not show any signs of illness, lameness or clinical signs consistent with PPID. Blood samples were collected 6 months apart, around the autumn equinox and spring equinox, and plasma concentrations of ACTH were measured by chemiluminescent immunoassay. Pairwise breed comparisons within each season were performed on log transformed data using the Tukey test. Estimated mean differences in ACTH concentrations were expressed as fold difference with 95 % confidence intervals (CI). Reference intervals for each breed group per season were calculated using non-parametric methods. In autumn, higher ACTH concentrations were found among non-Shetland pony breeds compared with Thoroughbreds (1.55 fold higher; 95 % CI, 1.35-1.77; P < 0.001), and in Shetland ponies compared with Thoroughbreds (2.67 fold higher; 95 % CI, 2.33-3.08; P < 0.001) and non-Shetland pony breeds (1.73 fold higher; 95 % CI, 1.51-1.98; P < 0.001). In spring, no differences were identified among breed groups (all P > 0.05). Reference intervals were similar among breed groups in spring, but upper limits for ACTH concentrations were markedly different between Thoroughbred horses and pony breeds in autumn. These findings emphasise that breed should be accounted for when determining and interpreting reference intervals for ACTH concentrations among healthy horses and ponies in autumn.
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Affiliation(s)
- N J Bamford
- Melbourne Veterinary School, The Universtiy of Melbourne, Building 400, Parkville, Victoria 3010, Australia.
| | - A J Stewart
- School of Veterinary Science, The University of Queensland, Building 4114, Gatton, Queensland 4343, Australia
| | - C M El-Hage
- Melbourne Veterinary School, The Universtiy of Melbourne, Building 400, Parkville, Victoria 3010, Australia
| | - F R Bertin
- School of Veterinary Science, The University of Queensland, Building 4114, Gatton, Queensland 4343, Australia
| | - S R Bailey
- Melbourne Veterinary School, The Universtiy of Melbourne, Building 400, Parkville, Victoria 3010, Australia
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14
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Clark BL, Bamford NJ, Stewart AJ, McCue ME, Rendahl A, Bailey SR, Bertin FR, Norton EM. Evaluation of an HMGA2 variant contribution to height and basal insulin concentrations in ponies. J Vet Intern Med 2023; 37:1186-1192. [PMID: 37148171 DOI: 10.1111/jvim.16723] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Accepted: 04/08/2023] [Indexed: 05/08/2023] Open
Abstract
BACKGROUND The HMGA2:c.83G>A variant was identified in Welsh ponies having pleiotropic effects on height and insulin concentration. OBJECTIVE Determine whether the HMGA2:c.83G>A variant is associated with decreased height and higher basal insulin concentrations across pony breeds. ANIMALS Two hundred thirty-six ponies across 6 breeds. METHODS Cross-sectional study. Ponies were genotyped for the HMGA2:c.83G>A variant and phenotyped for height and basal insulin concentrations. Stepwise regression was performed for model analysis using a linear regression model for height and mixed linear model for insulin with farm as a random effect. Coefficient of determination, pairwise comparison of the estimated marginal means and partial correlation coefficients (parcor) were calculated to assess the relationship between HMGA2 genotype and height or insulin. RESULTS Breed and genotype accounted for 90.5% of the variation in height across breeds, and genotype explained 21% to 44% of the variation within breeds. Breed, genotype, cresty neck score, sex, age, and farm accounted for 45.5% of the variation in insulin, with genotype accounting for 7.1%. The HMGA2 A allele frequency was 62% and correlated with both height (parcor = -0.39; P < .001) and insulin (parcor = 0.22; P = .02). Pairwise comparisons found A/A ponies were >10 cm shorter than other genotypes. Compared with G/G individuals, A/A and G/A individuals had 4.3 μIU/mL (95% confidence interval [CI]: 1.8-10.5) and 2.7 μIU/mL (95% CI: 1.4-5.3) higher basal insulin concentrations, respectively. CONCLUSIONS AND CLINICAL IMPORTANCE These data demonstrate the pleiotropic effects of the HMGA2:c.83G>A variant and its role in identifying ponies at increased risk for insulin dysregulation.
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Affiliation(s)
- Brianna L Clark
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
| | - Nicholas J Bamford
- Melbourne Veterinary School, The University of Melbourne, Parkville, Victoria, Australia
| | - Allison J Stewart
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
| | - Molly E McCue
- College of Veterinary Medicine, The University of Minnesota, St Paul, Minnesota, USA
| | - Aaron Rendahl
- College of Veterinary Medicine, The University of Minnesota, St Paul, Minnesota, USA
| | - Simon R Bailey
- Melbourne Veterinary School, The University of Melbourne, Parkville, Victoria, Australia
| | - François-René Bertin
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
| | - Elaine M Norton
- College of Agricultural and Life Sciences, The University of Arizona, Tucson, Arizona, USA
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15
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McGowan CM, Ireland JL. Equine Endocrine Disease: Challenges With Case Definition for Research. J Equine Vet Sci 2023; 124:104491. [PMID: 37236726 DOI: 10.1016/j.jevs.2023.104491] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Revised: 04/06/2023] [Accepted: 04/12/2023] [Indexed: 05/28/2023]
Abstract
Equine endocrine disease is an important area for equine research, requiring an appropriate case definition for inclusion and criteria for exclusion from disease. Defining a case for research may be different from criteria for clinical diagnosis. Further, clinical diagnosis recommendations have been changing regularly, making this area challenging for equine scientists. This review discusses the diagnosis of major equine endocrine diseases, pituitary pars intermedia dysfunction, equine metabolic syndrome and insulin dysregulation, focusing on the most appropriate diagnostic methods for research case definitions. Different diagnostic methods, including use of reference intervals and clinical decision limits, will be discussed with their relative merits for use in case definition for research.
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Affiliation(s)
- Catherine M McGowan
- School of Veterinary Science, Institute of Infection, Ecological and Veterinary Sciences, the University of Liverpool, Neston, UK.
| | - Joanne L Ireland
- School of Veterinary Science, Institute of Infection, Ecological and Veterinary Sciences, the University of Liverpool, Neston, UK
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16
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Manfredi JM, Jacob S, Norton E. A one-health lens offers new perspectives on the importance of endocrine disorders in the equine athlete. J Am Vet Med Assoc 2023; 261:153-164. [PMID: 36595370 DOI: 10.2460/javma.22.11.0485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Endocrine disorders are associated with joint pain and tendon injury in humans, but the effects in the horse are only starting to be understood. Similar patterns of clinical signs and injury appear to affect horses and humans for both orthopedic and endocrine disorders, supporting the use of a one-health approach to tackle these issues. In this Currents in One Health, we will discuss common equine endocrinopathies, current testing recommendations, dietary management, genetic predispositions, and endocrine disorders' effects on performance. Our aim is to use a one-health lens to describe current comparative research so that veterinarians can employ cutting-edge preventative, diagnostic, and therapeutic recommendations. Identified key gaps in knowledge include whether equine metabolic osteoarthritis exists, if steroid joint injections are safe in horses with endocrine disorders, and if the return to performance percentage improves with concurrent treatment of endocrine and musculoskeletal disorders. Key takeaways include that the relationship between endocrine disorders and musculoskeletal disease in the horse goes beyond laminitis to include lameness, muscle atrophy, suspensory ligament degeneration, osteochondritis dissecans, and potentially metabolic osteoarthritis. Approaches learned from human and equine comparative studies can offer insight into injury recognition and management, thus mitigating the impact of endocrine disorders on performance in both species. Readers interested in an in-depth description of current and future research involving pathophysiology, novel interventions, and multiomic approaches to identify individuals with athletic limitations induced by endocrine disorders are invited to read the companion Currents in One Health by Manfredi et al, AJVR, February 2023.
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Affiliation(s)
- Jane M Manfredi
- 1Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI
| | - Sarah Jacob
- 1Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI
| | - Elaine Norton
- 2Department of Animal and Comparative Biomedical Sciences, College of Agriculture and Life Sciences, University of Arizona, Tucson, AZ
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17
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Huang L, Palmieri C, Bertin FR. Correlation of pituitary histomorphometry with dopamine and dopamine D2 receptor expression in horses with pituitary pars intermedia dysfunction. Res Vet Sci 2022; 152:427-433. [PMID: 36126509 DOI: 10.1016/j.rvsc.2022.08.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Revised: 08/09/2022] [Accepted: 08/20/2022] [Indexed: 10/15/2022]
Abstract
Pituitary pars intermedia dysfunction (PPID) is an endocrinopathy commonly affecting old horses. It is a spontaneously occurring, progressive disease that is still poorly understood. Previous studies have observed neurodegeneration of the dopaminergic inhibition of melanotrophs, which leads to decreased dopamine (DA) in the pars intermedia (PI) and increased pro-opiomelanocortin-derived peptides circulating in plasma. However, rats knockout for the dopamine D2 receptor (D2r) similarly develop PI hypertrophy and hyperplasia. Thus, based on the current pathophysiological theory of PPID, whether the decreased DA or the D2r dysfunction leads to PPID is still unclear. To test this, a total of 28 retrospective cases of horses with PPID were collected, graded and the expression of tyrosine hydroxylase (TH) and D2r in the PI were determined. The histological and immunohistochemical results demonstrated that horses with higher tumor histological grades had reduced TH expression with increased D2r immunoreactivity colocalized in the PI (p < 0.001, p < 0.05 respectively). This correlation supports the role of DA in the pathogenesis of continuous unregulated proliferation of neoplastic cells in PI and indicates the efficiency of D2r agonists as a treatment for PPID.
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Affiliation(s)
- Luoyi Huang
- School of Veterinary Science, The University of Queensland, Gatton, Queensland 4343, Australia.
| | - Chiara Palmieri
- School of Veterinary Science, The University of Queensland, Gatton, Queensland 4343, Australia.
| | - François-René Bertin
- School of Veterinary Science, The University of Queensland, Gatton, Queensland 4343, Australia.
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18
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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; 9:vetsci9100572. [PMID: 36288186 PMCID: PMC9607114 DOI: 10.3390/vetsci9100572] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Revised: 09/29/2022] [Accepted: 10/11/2022] [Indexed: 12/31/2022] Open
Abstract
Simple Summary Pituitary pars intermedia dysfunction (PPID) is a common disease of the geriatric horse population. The most common clinical sign of PPID is hypertrichosis, or a long hair-coat with delayed shedding. Hypertrichosis is the most easily recognized clinical sign of PPID. However, the presence of hypertrichosis is often associated with severe end-stage disease. There is little research investigating sub-clinical or early PPID and the clinical signs associated with these stages of disease. The benefit of being able to recognize early PPID, is that we are able to begin treatment earlier on in disease process, potentially reducing the deleterious consequences of PPID and improving survival. Laboratory tests are available to more accurately diagnose PPID, and these tests include the basal ACTH and TRH-stimulated ACTH tests. Basal ACTH is easy to perform and is recommended in cases where clinical disease is suspected. The TRH-stimulation test improves diagnostic accuracy in early PPID cases. This study documents both test results and clinical signs associated with the transition from subclinical to clinical PPID, so that we are better able to recognize potential early PPID, as well as interpret results in these horses. Abstract Poor recognition of subtle clinical abnormalities and equivocal ACTH concentrations make early diagnosis of PPID difficult. Progressive clinical findings and corresponding ACTH concentrations in horses transitioning to PPID over time have not been documented. Seven horses with ACTH concentrations equivocal for PPID (utilizing locally derived, seasonally adjusted diagnostic-cut off values (DCOV)) and no clinical signs of PPID were selected. Sequential measurement of basal and thyrotropin-releasing hormone (TRH)-stimulated ACTH concentrations and recording of clinical findings occurred from October 2017 to November 2021 in a prospective case series. In two horses, marked hypertrichosis developed. Although 1/11 basal ACTH concentrations were below DCOV in 2018, subsequently all basal ACTH concentrations in these two horses without treatment were greater than DCOV. One horse was treated with pergolide which normalized basal ACTH concentrations. Four horses developed intermittent, mild hypertrichosis, and one horse never developed hypertrichosis. Basal ACTH concentrations in these five horses were greater than DCOV in 63/133 (47.4%) of testing points. TRH-stimulated ACTH concentrations in these five horses were greater than DCOV in 77/133 (57.9%) of testing points, sometimes markedly increased and greater than the assay upper limit of detection (LoD) of 1250pg/mL. TRH-stimulated ACTH concentrations were most frequently positive in late summer and early autumn, with 24/37 (64.9%) of TRH-stimulated ACTH concentrations greater than the DCOV in February and March. Horses transitioning to PPID can have subtle clinical signs and equivocal ACTH concentrations. However, TRH-stimulated ACTH concentrations can be markedly greater than DCOV, especially in late summer and early autumn (February and March) allowing for identification of subclinical and transitional cases.
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Affiliation(s)
- Naomi C. Kirkwood
- School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW 2678, Australia
| | - Kristopher J. Hughes
- School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW 2678, Australia
| | - Allison J. Stewart
- School of Veterinary Science, Gatton Campus, The University of Queensland, Gatton, QLD 4343, Australia
- Correspondence: ; Tel.: +61-754-601-799
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19
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Pituitary Pars Intermedia Dysfunction (PPID) in Horses. Vet Sci 2022; 9:vetsci9100556. [PMID: 36288169 PMCID: PMC9611634 DOI: 10.3390/vetsci9100556] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Revised: 09/25/2022] [Accepted: 10/04/2022] [Indexed: 12/12/2022] Open
Abstract
Substantial morbidity results from pituitary pars intermedia dysfunction (PPID) which is often underestimated by owners and veterinarians. Clinical signs, pathophysiology, diagnostic tests, and treatment protocols of this condition are reviewed. The importance of improved recognition of early clinical signs and diagnosis are highlighted, as initiation of treatment will result in improved quality of life. Future research should be targeted at improving the accuracy of the diagnosis of PPID, as basal adrenocorticotropic hormone (ACTH) concentration can lack sensitivity and thyrotropin releasing hormone (TRH) used to assess ACTH response to TRH stimulation is not commercially available as a sterile registered product in many countries. The relationship between PPID and insulin dysregulation and its association with laminitis, as well as additional management practices and long-term responses to treatment with pergolide also require further investigation.
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20
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Fisher D, Schliewert EC, Hooijberg EH. Temporally specific adrenocorticotropic hormone reference intervals for horses in South Africa. J S Afr Vet Assoc 2022; 93:116-123. [DOI: 10.36303/jsava.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023] Open
Affiliation(s)
- D Fisher
- Department of Companion Animal Clinical Studies, Faculty of Veterinary Science, University of Pretoria,
South Africa
| | - E-C Schliewert
- Department of Companion Animal Clinical Studies, Faculty of Veterinary Science, University of Pretoria,
South Africa
| | - EH Hooijberg
- Department of Companion Animal Clinical Studies, Faculty of Veterinary Science, University of Pretoria,
South Africa
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21
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Humphreys S, Kass PH, Magdesian KG, Goodrich E, Berryhill E. Seasonal variation of endogenous adrenocorticotropic hormone concentrations in healthy non-geriatric donkeys in Northern California. Front Vet Sci 2022; 9:981920. [PMID: 36032308 PMCID: PMC9412165 DOI: 10.3389/fvets.2022.981920] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 07/26/2022] [Indexed: 11/13/2022] Open
Abstract
Elevated plasma adrenocorticotropic hormone (ACTH) is often used to diagnose pituitary pars intermedia dysfunction (PPID) in horses. The hormone naturally increases in the fall in horses, and donkeys have been found to have higher ACTH concentrations than horses. However, circannual variation of ACTH has not been assessed in donkeys. The objective of the study was to establish seasonal variation of basal plasma ACTH concentrations over the course of a year in clinically healthy, non-geriatric donkeys. It was hypothesized that donkey ACTH concentrations would be higher than those reported in horses without PPID in all seasons, and that, similarly to horses, ACTH concentrations would further increase in the fall months. Twenty-six healthy adult donkeys (10 standards, 16 miniatures), a median (range) of 6 (2–13) years of age, were included. Donkeys were housed at a single location. Serial plasma samples were obtained monthly for 12 months. Plasma ACTH concentrations were determined by immunoassay. Data are presented as median (range), with a P-value < 0.05 considered significant. ACTH concentrations were lowest in the winter and spring [12.8 (5.0–73.6) pg/ml and 12.5 (2.8–62.6) pg/ml, respectively], with an increase in the summer [53.2 (29.7–305.0) pg/ml], and peak in the fall [77.1 (12.4–319.0) pg/ml]. ACTH concentrations were highest in the month of September [122.0 (41.7–319.0) pg/ml]. Donkey ACTH concentrations were higher than equine reference ranges from May through November but showed similar circannual variation with dramatic increases in the fall months. Species-specific reference ranges are necessary for accurate interpretation of endocrinopathy screenings in donkeys.
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Affiliation(s)
- Sarah Humphreys
- School of Veterinary Medicine, University of California, Davis, Davis, CA, United States
| | - Philip H. Kass
- Department of Population Health and Reproduction, University of California, Davis, Davis, CA, United States
| | - K. Gary Magdesian
- Department of Medicine and Epidemiology, University of California, Davis, Davis, CA, United States
| | - Erin Goodrich
- Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY, United States
| | - Emily Berryhill
- Department of Medicine and Epidemiology, University of California, Davis, Davis, CA, United States
- *Correspondence: Emily Berryhill
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22
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Durham A, Potier J, Huber L. The effect of month and breed on plasma adrenocorticotropic hormone concentrations in equids. Vet J 2022; 286:105857. [DOI: 10.1016/j.tvjl.2022.105857] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 06/22/2022] [Accepted: 07/01/2022] [Indexed: 11/16/2022]
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23
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Durham AE. The effect of pergolide mesylate on adrenocorticotrophic hormone responses to exogenous thyrotropin releasing hormone in horses. Vet J 2022; 285:105831. [PMID: 35477010 DOI: 10.1016/j.tvjl.2022.105831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Revised: 03/08/2022] [Accepted: 04/21/2022] [Indexed: 10/18/2022]
Abstract
Thyrotropin releasing hormone (TRH) stimulation testing is often used to support a diagnosis of pituitary pars intermedia dysfunction (PPID) in horses although it is unclear whether or not repeat TRH stimulation testing post-treatment is a valid means of assessing response to medical therapy. Laboratory submissions from 64 suspected equine PPID cases were examined including the initial pre-treatment TRH stimulation test and a follow up test within 100 days of starting medical therapy with pergolide. In a subset of cases, further follow-up tests were examined beyond 100 days of starting treatment. Results from tests conducted between 1 July and 30 November 30 were excluded. Significant improvements were seen in both the baseline and TRH-stimulated adrenocorticotrophic hormone (ACTH) concentrations within 100 days with no further improvements seen in the subset of cases examined thereafter. Although 88% (n=56/64) of all cases showed a decreased response to TRH post-treatment, only 24% (n=9/38) of horses with positive pre-treatment TRH stimulation tests normalised following treatment, with a further 34% (n=13/38) improving into an equivocal test outcome category. Most commonly (42%; n=16/38), horses with positive pre-treatment TRH stimulation tests remained positive following treatment, although 75% (n=12/16) of these showed a numerically lower post-treatment response to TRH. These results will help inform practitioners of expected changes in TRH stimulation test results when assessing response of horses with PPID to medical therapy with pergolide.
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Affiliation(s)
- A E Durham
- Liphook Equine Hospital, Liphook, Hampshire GU30 7JG, UK.
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24
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Hinrichsen SL, Yuen KY, Dryburgh EL, Bertin FR, Stewart AJ. Short-Term Effects of Temperature and Thyrotropin-Releasing Hormone Stimulation on Adrenocorticotropin Stability in Horses. Animals (Basel) 2022; 12:ani12030324. [PMID: 35158648 PMCID: PMC8833476 DOI: 10.3390/ani12030324] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 01/11/2022] [Accepted: 01/24/2022] [Indexed: 01/30/2023] Open
Abstract
Pituitary pars intermedia dysfunction (PPID) is diagnosed by increased basal or post thyrotropin-releasing hormone (TRH) stimulation ACTH concentrations. ACTH is known to be unstable; however, the effect of different temperatures and TRH stimulation on equine ACTH stability is poorly described. In total, 15 horses, including 8 PPID positive (ACTH > 35 pg/mL at baseline or >65 pg/mL 30 min after TRH stimulation), were divided into 2 groups: 9, including 5 PPID positive, with basal ACTH concentrations and 6, including 3 PPID positive, with post TRH stimulation ACTH concentrations. Whole blood was stored for 1 h at 4, 20, 30, 40, or 70 °C. After centrifugation, immunoreactive ACTH concentrations were determined using a chemiluminescent assay. Linear mixed effect models were used to detect the effects of temperature, PPID status, and TRH stimulation on the immunoreactive ACTH concentration. Temperature had a significant effect (p = 0.003) on immunoreactive ACTH concentrations, and this effect was greater in PPID-negative horses (p = 0.01), with the changes in immunoreactive ACTH concentrations being slightly unpredictably higher or lower than samples stored at 4 °C. Even at 20 °C, mean immunoreactive ACTH concentrations minimally changed by 5% in PPID horses and 12% in non-PPID horses after 1 h. No significant effect of TRH stimulation was identified. Although ACTH concentrations should ideally be determined from samples kept at 4 °C, samples inadvertently left at temperatures of up to 40 °C can provide valid results if analyzed within 1 h; however, this increases the risks of altered ACTH concentrations, occasionally influencing the diagnosis of PPID.
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Affiliation(s)
- Sophia L. Hinrichsen
- School of Veterinary Science, The University of Queensland, Gatton, QLD 4343, Australia; (S.L.H.); (K.Y.Y.); (F.-R.B.)
| | - Ka Y. Yuen
- School of Veterinary Science, The University of Queensland, Gatton, QLD 4343, Australia; (S.L.H.); (K.Y.Y.); (F.-R.B.)
| | - Elizabeth L. Dryburgh
- Boehringer Ingelheim Animal Health Australia Pty. Ltd., North Ryde, NSW 2113, Australia;
| | - François-René Bertin
- School of Veterinary Science, The University of Queensland, Gatton, QLD 4343, Australia; (S.L.H.); (K.Y.Y.); (F.-R.B.)
| | - Allison J. Stewart
- School of Veterinary Science, The University of Queensland, Gatton, QLD 4343, Australia; (S.L.H.); (K.Y.Y.); (F.-R.B.)
- Correspondence: ; Tel.: +61-7-54601-799
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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; 36:770-777. [PMID: 35049089 PMCID: PMC8965261 DOI: 10.1111/jvim.16362] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 01/05/2022] [Accepted: 01/07/2022] [Indexed: 01/21/2023] Open
Abstract
Background Diagnosis of pituitary pars intermedia dysfunction (PPID) using the thyrotropin‐releasing hormone (TRH) stimulation test requires blood collection 10 minutes after TRH injection; it is unknown if small differences in timing affect test results. Objective To determine whether early or late sampling results in a significant (≥10%) difference in plasma adrenocorticotropic hormone (ACTH) concentration compared to standard 10‐minute sampling. Animals Twenty‐four healthy adult horses with unknown PPID status. Methods In this prospective study, subjects underwent a single TRH stimulation test, with blood collected exactly 9 minutes (early), 10 minutes (standard), and 11 minutes (late) after injection. ACTH was measured by chemiluminescent immunoassay. Two aliquots of the 10‐minute plasma sample were analyzed separately to assess intra‐assay variability. Data were reported descriptively and bias was calculated using Bland‐Altman plots. Significance was set at P = .05. Results Minor variability was observed between the paired 10‐minute sample aliquots (range, 0%‐6%; median 3%). Overall variability of early or late samples compared to the corresponding paired (average) 10‐minute standard concentration ranged from 0% to 92% (median 10%). Seventy‐five percent of horses (18/24) tested had at least 1 early or late reading that differed by ≥10% from its corresponding 10‐minute standard concentration, and 21% of horses (5/24) would have a different interpretation of testing result with either early or late sampling. Incidence of ≥10% variability was independent of PPID status (P = .59). Conclusions and Clinical Importance Precise timing of sample collection is critical to ensure accurate assessment of PPID status given the observation of significant variability associated with minor alterations in timing of sample collection.
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Affiliation(s)
- Kristen Thane
- Tufts Cummings School of Veterinary Medicine, Department of Comparative Pathobiology, North Grafton, Massachusetts, USA
| | - Cassandra Uricchio
- University of Massachusetts, Department of Veterinary and Animal Sciences, Amherst, Massachusetts, USA
| | - Nicholas Frank
- Tufts Cummings School of Veterinary Medicine, Department of Comparative Pathobiology, North Grafton, Massachusetts, USA
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Kam YN, McKenzie K, Coyle M, Bertin FR. Repeatability of a thyrotropin-releasing hormone stimulation test for diagnosis of pituitary pars intermedia dysfunction in mature horses. J Vet Intern Med 2021; 35:2885-2890. [PMID: 34642962 PMCID: PMC8692209 DOI: 10.1111/jvim.16281] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 09/27/2021] [Accepted: 10/01/2021] [Indexed: 01/14/2023] Open
Abstract
BACKGROUND Pituitary pars intermedia dysfunction (PPID) is a common endocrinopathy of horses diagnosed with a thyrotropin-releasing hormone (TRH) stimulation test. HYPOTHESIS/OBJECTIVES Describe the repeatability of TRH stimulation in horses with and without PPID in winter and autumn. ANIMALS Twenty adult horses; 6 controls and 6 with PPID tested in autumn, 8 controls and 6 with PPID tested in winter with 3 controls and 3 with PPID tested in both seasons. METHODS Thyrotropin-releasing hormone stimulation was performed on 2 consecutive occasions, 1 week before and 1 week after the winter solstice and the autumn equinox. Blood was collected before and 30 minutes after IV injection of 1 mg of TRH. ACTH concentration was determined by a chemiluminescent assay. Repeatability and test-retest reliability were assessed by repeated measures analysis of variance, intraclass correlation coefficient and within-horse coefficients of variation (CV). Bland-Altman plots were generated to visualize agreement between repetitions. RESULTS In winter, no week effect was detected on the results of the TRH simulation and the test had an excellent test-retest reliability. In autumn, after-TRH ACTH concentrations were significantly lower on week 2 (P = .02) and the test only had a good test-retest reliability. There were significantly larger within-horse CV during autumn (P = .04) and after TRH stimulation (P = .04). There were 2 misclassifications in winter and 4 in autumn. CONCLUSIONS AND CLINICAL IMPORTANCE The TRH stimulation test was repeatable when performed 2 weeks apart in winter; however, in autumn, more variability in after-TRH ACTH concentrations resulted in decreased repeatability.
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Affiliation(s)
- Yan Ning Kam
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
| | - Kelly McKenzie
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
| | - Mitchell Coyle
- Office of the Director of Gatton Campus, The University of Queensland, Gatton, Queensland, Australia
| | - François-René Bertin
- School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia
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Meyer JC, Hunyadi LM, Ordóñez-Mena JM. The accuracy of ACTH as a biomarker for pituitary pars intermedia dysfunction in horses: A systematic review and meta-analysis. Equine Vet J 2021; 54:457-466. [PMID: 34428330 DOI: 10.1111/evj.13500] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 06/15/2021] [Accepted: 08/19/2021] [Indexed: 02/01/2023]
Abstract
BACKGROUND Accuracy of baseline ACTH for the diagnosis of PPID in horses varies between studies. OBJECTIVES To estimate the diagnostic accuracy of ACTH as a biomarker for PPID in adult horses and appraise potential causes of heterogeneity. STUDY DESIGN Systematic review and meta-analysis. METHODS A literature review identified studies reporting diagnostic accuracy data for extraction. Risk of bias was evaluated using QUADAS-2. Two random-effects models, the hierarchical summary receiver operating curve (HSROC) and the bivariate binomial normal model (BBN) were used to pool accuracy measurements. We performed meta-regression using study-level variables. The impact of diagnostic test accuracy on the frequency of false-positive and false-negative results at various pretest probabilities was calculated using the BBN model's accuracy results. RESULTS Patient selection and index test evaluation demonstrated significant risk of bias. Mean and 95% confidence intervals for sensitivity and specificity for all studies (n = 11) based upon the HSROC model were (0.72, 95% CI: 0.62 to 0.82) and (0.88, 95% CI: 0.79 to 0.93), respectively. When studies with a common positivity threshold of 35 pg/mL ACTH were evaluated (n = 6), sensitivity and specificity were (0.66, 95% CI:0.54 to 0.77) and (0.87, 95% CI: 0.74 to 0.94). In a hypothetical group of one thousand horses with PPID prevalence of 2%, 20%, and 90%, the frequency of resulting false-positive and false-negatives would be (127 and 7), (104 and 68) and (13 and 306), respectively. Factors leading to increased accuracy were case-control design, clinical reference standard and data-driven choice of ACTH threshold. MAIN LIMITATIONS A small number of primary studies (n = 11) were available, demonstrating significant biases. CONCLUSIONS Less biased studies examining diagnostic accuracy of ACTH are needed. In horses with a high pretest probability of PPID, ACTH may be a functional "rule-in" test. Baseline ACTH is not recommended for screening purposes or use in horses without clinical signs of PPID.
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Affiliation(s)
| | - László M Hunyadi
- School of Veterinary Medicine, Texas Tech University, Lubbock, Texas, USA
| | - José M Ordóñez-Mena
- Nuffield Department of Primary Care Health Sciences - University of Oxford, Oxford, UK
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Evaluation of the sensitivity and specificity of basal plasma adrenocorticotrophic hormone concentration for diagnosing pituitary pars intermedia dysfunction in horses: A systematic review. Vet J 2021; 275:105695. [PMID: 34099343 DOI: 10.1016/j.tvjl.2021.105695] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Revised: 04/12/2021] [Accepted: 05/19/2021] [Indexed: 02/01/2023]
Abstract
Measurement of basal adrenocorticotrophic hormone (ACTH) is currently used to diagnose pituitary pars intermedia dysfunction (PPID) in horses, yet a systematic review of the evidence for its use has not been undertaken. This study aimed to systematically review evidence regarding the sensitivity and specificity of the basal ACTH diagnostic test. Electronic databases were systematically searched in January 2019, September 2020 and January 2021, for English language publications published prior to these dates. Screening, data extraction and quality assessment of publications was undertaken by the authors using predefined criteria. Study design, methodology and information reported in included studies were assessed using Standards for Reporting of Diagnostic Accuracy (STARD) checklists. Risk of bias and applicability were appraised using the Quality Assessment tool for Diagnostic Accuracy Studies (QUADAS-2) quality assessment tool. Due to identified biases and marked between-study variations, meta-analysis was not undertaken. After removal of duplicates, 415 publications were identified, of which 25 were evaluated in full, with 11 of these meeting inclusion criteria. In most studies, basal ACTH was reported to have good sensitivity (overall median 75.5%; interquartile range [IQR], 64.0-86.5%; range, 36.0-100%) and excellent specificity (overall median, 95.2%; IQR, 84.2-98.9%; range, 63.3-100%). However, QUADAS-2 and STARD assessment highlighted that studies did not utilise optimal study design and/or study populations for the evaluation of a diagnostic test and the majority were subject to bias, or provided insufficient information to fully assess possible biases. Based on this review, basal ACTH performed better at ruling out PPID than detecting it.
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Changes Associated with the Peri-Ovulatory Period, Age and Pregnancy in ACTH, Cortisol, Glucose and Insulin Concentrations in Mares. Animals (Basel) 2021; 11:ani11030891. [PMID: 33804751 PMCID: PMC8003915 DOI: 10.3390/ani11030891] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 03/17/2021] [Accepted: 03/18/2021] [Indexed: 11/17/2022] Open
Abstract
Simple Summary The reproductive cycle of mares is associated with many hormonal changes, but the effects of this cycle and pregnancy on adrenocorticotropic hormone and insulin concentrations are poorly described, which could limit our ability to diagnose pituitary pars intermedia dysfunction and insulin dysregulation. In this study, healthy mares are followed through their reproductive cycle during the physiologic breeding season, and adrenocorticotropic hormone, cortisol, glucose and insulin concentrations are measured to determine the effects of age, pregnancy and the reproductive cycle on analyte concentrations. No significant effect of age, the reproductive cycle or pregnancy is detected on the cortisol, glucose or insulin concentrations; however, adrenocorticotropic hormone concentrations are significantly increased throughout the peri-ovulatory period and during pregnancy. Therefore, knowledge of a mare’s reproductive cycle might be beneficial when interpreting adrenocorticotropic hormone concentrations. Abstract Although there are many hormonal changes associated with reproduction, the effects of ovulation and early pregnancy on adrenocorticotropic hormone (ACTH) and insulin concentrations are poorly described. We hypothesise that both ovulation and early pregnancy will alter ACTH and insulin concentrations in healthy mares. Eighteen mares showing no clinical signs suggestive of, or laboratory findings consistent with, pituitary pars intermedia dysfunction PPID and insulin dysregulation (ID) are enrolled. ACTH, cortisol, insulin and glucose concentrations are measured over their peri-ovulatory period, as determined via ultrasounds and progesterone concentrations. The mares are grouped by age and gestation status, and a two-way repeated-measures ANOVA is used to determine the effects of age and early pregnancy, along with the peri-ovulatory period, on analyte concentrations. No significant effect of age, ovulation or early pregnancy is detected on the mares’ cortisol, insulin or glucose concentrations; however, there is a significant effect of early pregnancy and ovulation on ACTH concentrations (p = 0.04 and p = 0.04 respectively). ACTH concentrations change around ovulation and with early pregnancy. Therefore, knowledge of a mare’s reproductive status might be beneficial when interpreting ACTH concentrations.
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