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Veterinary sciences2022; 9(10); 572; doi: 10.3390/vetsci9100572

Prospective Case Series of Clinical Signs and Adrenocorticotrophin (ACTH) Concentrations in Seven Horses Transitioning to Pituitary Pars Intermedia Dysfunction (PPID).

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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Publication Date: 2022-10-17 PubMed ID: 36288186PubMed Central: PMC9607114DOI: 10.3390/vetsci9100572Google Scholar: Lookup
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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 research article investigates the progression of clinical signs and adrenocorticotropin (ACTH) concentrations in seven horses potentially developing Pituitary Pars Intermedia Dysfunction (PPID). The research, conducted from October 2017 to November 2021, notes that early diagnosis is difficult due to slight clinical abnormalities and equivocal ACTH concentrations. The study provides in-depth insight into the symptoms and ACTH concentration changes in horses transitioning to PPID.

Research Methodology

  • The study selected seven horses that had ACTH concentrations on the borderline of PPID, calculated using locally adapted, seasonally adjusted diagnostic cut-off values (DCOV). The selected horses did not display clear signs of PPID initially.
  • The researchers performed sequential measurement of basal (natural) and thyrotropin-releasing hormone (TRH) stimulated ACTH concentrations over the course of four years. Along with this, they recorded clinical findings to keep track of the development of other symptoms.

Research Findings

  • Out of the seven horses, two developed significant hypertrichosis (excessive hair growth), a symptom associated with PPID. Though their basal ACTH concentrations in 2018 were below the DCOV, subsequent tests showed a continuous increase in ACTH levels, even without any treatment.
  • One of these two horses was treated with a drug called pergolide, which brought the ACTH concentrations back to normal ranges.
  • Four of the remaining five horses displayed mild, intermittent hypertrichosis while the ACTH concentrations in these horses exceeded the DCOV in nearly half of the tests performed.
  • The final horse didn’t display hypertrichosis and the ACTH measures were relatively unchanged.
  • However, when ACTH concentrations were induced with TRH, the ACTH values for these five horses were significantly above DCOV and sometimes exceeded the maximum limit of detection for the tests. This reaction was most frequent in late summer and early autumn, or specifically in February and March.

Conclusion

  • This study highlighted that horses transitioning to PPID may display subtle clinical signs and show ACTH concentrations around the borderline of PPID.
  • Interestingly, by stimulating ACTH concentrations using TRH, the ACTH levels can often significantly surpass the DCOV. This method proves particularly useful for detection in late summer and early autumn, aiding in the identification of cases in the early or subclinical stages.

Cite This Article

APA
Kirkwood NC, Hughes KJ, Stewart AJ. (2022). Prospective Case Series of Clinical Signs and Adrenocorticotrophin (ACTH) Concentrations in Seven Horses Transitioning to Pituitary Pars Intermedia Dysfunction (PPID). Vet Sci, 9(10), 572. https://doi.org/10.3390/vetsci9100572

Publication

Veterinary sciences
ISSN: 2306-7381
NlmUniqueID: 101680127
Country: Switzerland
Language: English
Volume: 9
Issue: 10
PII: 572

Researcher Affiliations

Kirkwood, Naomi C
  • School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW 2678, Australia.
Hughes, Kristopher J
  • School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW 2678, Australia.
Stewart, Allison J
  • School of Veterinary Science, Gatton Campus, The University of Queensland, Gatton, QLD 4343, Australia.

Conflict of Interest Statement

The authors declare no conflict of interest.

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Citations

This article has been cited 3 times.
  1. 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
  2. Goodrich EL, Llanos-Soto SG, Ivanek R, Pinn-Woodcock T, Frye E, Wells A, Purdy SR, Berryhill E, Place NJ. Both Season and Equid Type Affect Endogenous Adrenocorticotropic Hormone Concentrations in Healthy Donkeys, Mules and Hinnies in the United States. Animals (Basel) 2026 Jan 16;16(2).
    doi: 10.3390/ani16020290pubmed: 41594480google scholar: lookup
  3. Menzies-Gow NJ. Equine Pituitary Pars Intermedia Dysfunction. Vet Sci 2025 Aug 20;12(8).
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