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Home / Equine Research Bank / Vet Sci / Equine Pituitary Pars Intermedia Dysfunction.
Veterinary sciences2025; 12(8); 780; doi: 10.3390/vetsci12080780

Equine Pituitary Pars Intermedia Dysfunction.

Abstract: Pituitary pars intermedia dysfunction (PPID) is a common, slowly progressive, neurodegenerative disorder of the older horse. Oxidative damage to the hypothalamic periventricular neurons results in loss of dopaminergic inhibition of the pars intermedia region of the pituitary gland. Consequently, there is increased production of the pro-opiomelanocortin (POMC)-derived hormones normally produced by this region, as well as initial melanocyte hypertrophy and hyperplasia, followed by adenomatous change. Clinical signs that are highly suggestive of the disease are generalised and regional hypertrichosis and delayed/abnormal coat shedding. Numerous clinical signs provide a moderate clinical suspicion, including hyperhidrosis, abnormal fat distribution/regional adiposity, epaxial muscle atrophy/loss of topline, laminitis, weight loss, recurrent infections, behavioural changes/lethargy, polyuria and polydipsia, a pot-bellied appearance, bulging supraorbital fat pads, reduced wound healing, lordosis and infertility. In all animals, a diagnosis of PPID is made based on the signalment, clinical signs and results of further diagnostic tests, with age being a crucial factor to consider. Currently recommended further diagnostic tests are measurement of basal adrenocorticotrophic hormone (ACTH) concentrations (all year) and evaluation of the ACTH response to thyrotrophin-releasing hormone (TRH) using seasonally adjusted references intervals (non-autumn). Animals should also be tested for insulin dysregulation, as laminitis risk in PPID is associated with hyperinsulinaemia. PPID can be managed but not cured; it is a lifelong condition. The individual clinical signs can be managed, e.g., clipping the excessive haircoat and providing unrestricted access to water for individuals with polydipsia. Alternatively, pharmacological management can be employed, and the dopamine-2 receptor agonist pergolide is licensed/approved for the treatment of equine PPID. This should be prescribed in combination with dietary recommendations based on the body condition score and insulin sensitivity status of the individual animal.
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Publication Date: 2025-08-20 PubMed ID: 40872730PubMed Central: PMC12390634DOI: 10.3390/vetsci12080780Google 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.

Equine Pituitary Pars Intermedia Dysfunction (PPID) is a common neurodegenerative disorder affecting older horses, characterized by hormonal imbalances due to damage in the brain region regulating the pituitary gland. This leads to various clinical signs and can be diagnosed through specific hormone tests and clinical evaluation, with management focusing on symptom control and pharmaceutical treatment.

Introduction and Cause

  • PPID is a slowly progressive neurodegenerative disease affecting older horses.
  • It results from oxidative damage to hypothalamic periventricular neurons.
  • This damage causes a loss of dopaminergic inhibition of the pars intermedia region of the pituitary gland.
  • The disruption leads to increased production of hormones derived from pro-opiomelanocortin (POMC), hormones normally produced by this pituitary region.
  • Histological changes start with melanocyte hypertrophy and hyperplasia, eventually leading to adenomatous changes in the pars intermedia.

Clinical Signs

  • Highly suggestive signs include generalized and regional hypertrichosis (excessive hair growth) and delayed or abnormal shedding of the coat.
  • Additional clinical signs that raise suspicion for PPID include:
    • Hyperhidrosis (excessive sweating)
    • Abnormal fat distribution or regional adiposity
    • Epaxial muscle atrophy leading to loss of topline
    • Laminitis (inflammation of the hoof laminae)
    • Weight loss
    • Recurrent infections
    • Behavioral changes or lethargy
    • Polyuria (increased urination) and polydipsia (increased thirst)
    • Pot-bellied appearance
    • Bulging supraorbital fat pads
    • Reduced wound healing
    • Lordosis (abnormal curvature of the spine)
    • Infertility

Diagnosis

  • Diagnosis is based on:
    • Signalment (age and breed of the horse, with older age a critical factor)
    • Presence of clinical signs
    • Results of specific diagnostic tests
  • Diagnostic tests include:
    • Measurement of basal adrenocorticotrophic hormone (ACTH) concentrations year-round.
    • Assessment of ACTH response to thyrotrophin-releasing hormone (TRH) stimulation, using seasonally adjusted reference intervals outside the autumn season.
    • Testing for insulin dysregulation, because hyperinsulinemia increases the risk of laminitis in PPID horses.

Management and Treatment

  • PPID is a lifelong, manageable but currently incurable disease.
  • Management strategies include:
    • Symptomatic relief such as clipping the excessive hair coat.
    • Providing unrestricted access to water especially for horses with polydipsia.
  • Pharmacological treatment involves:
    • Use of pergolide, a dopamine-2 receptor agonist, which is licensed and approved for treating equine PPID.
    • Prescription of pergolide should be combined with dietary management tailored to the individual’s body condition score and insulin sensitivity.

Cite This Article

APA
Menzies-Gow NJ. (2025). Equine Pituitary Pars Intermedia Dysfunction. Vet Sci, 12(8), 780. https://doi.org/10.3390/vetsci12080780

Publication

Veterinary sciences
ISSN: 2306-7381
NlmUniqueID: 101680127
Country: Switzerland
Language: English
Volume: 12
Issue: 8
PII: 780

Researcher Affiliations

Menzies-Gow, Nicola J
  • Department of Clinical Science and Services, Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire AL9 7TA, UK.

Conflict of Interest Statement

The author declares no conflicts of interest.

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