Equine Pituitary Pars Intermedia Dysfunction
Authors: McFarlane Dianne
Journal: Veterinary Clinics of North America: Equine Practice
Summary
Pituitary pars intermedia dysfunction (PPID) represents a degenerative condition of the equine hypothalamus that becomes increasingly prevalent in older horses, characterised by oxidative damage to dopaminergic neurons and consequent loss of inhibitory control over POMC hormone production from the pituitary gland. The clinical presentation is highly variable—whilst persistent hypertrichosis and abnormal coat shedding are pathognomonic signs, practitioners should maintain clinical suspicion for PPID when encountering regional adiposity, epaxial muscle atrophy, recurrent laminitis (particularly when linked to hyperinsulinaemia), polydipsia, polyuria, or unexplained behavioural changes, especially in horses over 15 years of age. Diagnosis requires integration of signalment, clinical observation, and biochemical confirmation through basal ACTH measurement and TRH stimulation testing using seasonally adjusted reference ranges, with concurrent assessment of insulin sensitivity given the tight association between hyperinsulinaemia and laminitis risk in affected animals. Although PPID cannot be cured, pergolide (a dopamine-2 receptor agonist) provides effective pharmacological management and should be combined with tailored dietary intervention based on individual body condition and insulin status. This multifaceted approach—encompassing pharmacotherapy, nutritional management, and clinical monitoring—enables practitioners across disciplines to mitigate clinical signs and maintain quality of life in what will be a lifelong condition for affected horses.
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Practical Takeaways
- •PPID is a lifelong condition in older horses that cannot be cured but can be managed; excessive or abnormal hair coat shedding should prompt diagnostic testing in horses aged 15+ years
- •Test PPID-affected horses for insulin dysregulation as laminitis risk is directly associated with hyperinsulinaemia; dietary management specific to insulin sensitivity is essential alongside pergolide therapy
- •Combine pharmacological treatment (pergolide) with tailored nutrition and symptomatic management (e.g., clipping, unrestricted water access) for optimal clinical outcomes
Key Findings
- •PPID is a slowly progressive neurodegenerative disorder caused by oxidative damage to hypothalamic dopaminergic neurons, resulting in loss of inhibition of pars intermedia POMC hormone production
- •Generalized and regional hypertrichosis with delayed or abnormal coat shedding are the most specific clinical signs of PPID
- •Diagnosis is based on signalment, clinical signs, basal ACTH concentrations, and ACTH response to TRH stimulation using seasonally adjusted reference intervals
- •Pergolide (dopamine-2 receptor agonist) is the approved pharmacological treatment, and should be combined with dietary management tailored to body condition and insulin sensitivity status