Diagnosis of equine pituitary pars intermedia dysfunction.
Authors: Stewart Allison J, Ireland Joanne L, Durham Andy E, McGowan Catherine M
Journal: Veterinary journal (London, England : 1997)
Summary
Equine pituitary pars intermedia dysfunction (PPID) represents a significant clinical challenge in geriatric horses, demanding reliable diagnostic approaches given that affected animals require lifelong pharmacological management. Allison and colleagues reviewed the diagnostic landscape for PPID, emphasising that no single laboratory test provides perfect accuracy—a reality compounded by the fact that test performance varies substantially depending on the population being evaluated. Basal adrenocorticotropic hormone (ACTH) concentration remains the most commonly employed diagnostic tool in practice and demonstrates excellent diagnostic accuracy when interpreted alongside clinical presentation and appropriate reference thresholds specific to the testing laboratory and season. For cases yielding equivocal basal ACTH results, or when subtle disease manifestations warrant further investigation, the thyrotropin-releasing hormone stimulation test offers superior diagnostic sensitivity. Clinicians should recognise that PPID diagnosis hinges not on any single test in isolation, but rather on integrating biochemical findings with careful clinical evaluation—an approach that optimises diagnostic accuracy and reduces the risk of unnecessary lifelong treatment in misdiagnosed animals.
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Practical Takeaways
- •Use basal ACTH testing as your first-line diagnostic approach, but always interpret results in the context of clinical signs rather than relying on the test alone
- •If basal ACTH results are unclear or clinical suspicion remains high, request the TRH stimulation test to improve diagnostic confidence before committing to lifelong treatment
- •Remember that PPID is common in aged horses and most respond well to treatment, so don't dismiss clinical signs just because a single test is borderline
Key Findings
- •Basal ACTH concentration is the most frequently used diagnostic test for PPID and demonstrates very good diagnostic accuracy when combined with clinical judgement and appropriate diagnostic thresholds
- •Thyrotropin-releasing hormone stimulation test provides improved accuracy for evaluating equivocal basal ACTH results or subtle PPID cases
- •Accurate PPID diagnosis is critical because treatment is lifelong in horses that respond positively