Evaluation of dynamic testing for pituitary pars intermedia dysfunction diagnosis in donkeys.
Authors: Mejia-Pereira S, Perez-Ecija A, Buchanan B R, Toribio R E, Mendoza F J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Dynamic Testing for Equine PPID in Donkeys Pituitary pars intermedia dysfunction (PPID) is increasingly recognised as a significant endocrine disorder in ageing donkeys, yet diagnostic protocols have been largely extrapolated from horse medicine without validation in this species. Mejia-Pereira and colleagues evaluated three dynamic diagnostic tests—dexamethasone suppression test (DST), thyrotropin-releasing hormone (TRH) stimulation, and a combined DST-TRH challenge—in six donkeys with clinical signs suggestive of PPID, comparing results against established equine diagnostic guidelines. The TRH stimulation test proved the most reliable, successfully identifying PPID in all six donkeys, whereas DST alone detected only three cases and the combined challenge identified four, with notably inconsistent cortisol baseline concentrations further complicating diagnosis. These findings suggest that whilst TRH stimulation may be a suitable screening tool for donkey PPID, the DST protocols developed for horses do not translate effectively to this species, necessitating species-specific validation before being routinely applied in practice. Given the high prevalence of PPID in older donkeys and the potential for misdiagnosis using equine-derived thresholds, practitioners should consider TRH challenge as their first-line dynamic test, whilst acknowledging that larger prospective studies are urgently needed to establish donkey-specific diagnostic cut-off values and optimal testing protocols.
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Practical Takeaways
- •If suspecting PPID in donkeys, use TRH stimulation test rather than relying solely on dexamethasone suppression testing, as DST shows poor sensitivity in this species
- •Baseline ACTH measurement followed by TRH challenge should be your first-line diagnostic protocol for donkey PPID, not the horse-standard DST approach
- •Be aware that seasonal variation and geographical factors may influence baseline ACTH concentrations in donkeys—consider these factors when interpreting baseline results
Key Findings
- •TRH stimulation test successfully diagnosed PPID in all 6 donkeys (6/6), while DST detected only 3/6 cases and DST-TRH detected 4/6 cases
- •Baseline cortisol concentrations were not consistent with PPID suspicion in this donkey population
- •Horse-based PPID diagnostic guidelines appear applicable to donkeys but with important differences in test sensitivity
- •TRH stimulation test combined with baseline ACTH measurement are recommended as the primary diagnostic approach for PPID in donkeys