Pituitary Pars Intermedia Dysfunction
Authors: McFarlane Dianne, Johnson Philip J., Schott Harold C.
Journal: Equine Laminitis
Summary
# Editorial Summary: Pituitary Pars Intermedia Dysfunction Clinical signs in geriatric horses are often attributed to pituitary pars intermedia dysfunction (PPID), yet distinguishing age-related decline from endocrine disease remains challenging in practice. McFarlane and colleagues examined 113 horses aged 18–32 years using a cross-sectional design, measuring plasma beta-endorphin (β-END), adrenocorticotropic hormone (ACTH), and serum cortisol whilst scoring clinical signs including haircoat quality, muscle condition, weight, and behaviour. β-END and ACTH concentrations showed strong associations with haircoat abnormalities (P < 0.001)—the hallmark signs of PPID—with PPID-affected horses displaying substantially elevated β-END (median 291 pg/mL versus 55.0 pg/mL in controls, P < 0.001); conversely, muscle atrophy, weight loss, and lethargy correlated with advancing age rather than hormone concentrations, and cortisol levels were not linked to any clinical signs. These findings emphasise that farriers, veterinarians, and other practitioners should recognise that progressive muscle wasting and generalised decline may reflect normal ageing rather than PPID requiring treatment, whilst poor haircoat quality warrants ACTH testing to confirm endocrine dysfunction. Accurately distinguishing age-related changes from true PPID has significant implications for diagnostic protocols, targeted intervention, and preventing unnecessary medication in older horses.
Read the full abstract on PubMed
Practical Takeaways
- •Poor haircoat and abnormal shedding are the most reliable clinical indicators of PPID and warrant ACTH testing; don't assume muscle loss or lethargy in old horses are always PPID-related.
- •When evaluating geriatric horses, differentiate age-related decline (muscle atrophy, weight loss) from PPID signs (coat changes) to avoid over-diagnosis and unnecessary treatment.
- •Cortisol measurements are not useful for PPID diagnosis or assessment of clinical signs—focus on ACTH and β-endorphin concentrations alongside clinical presentation.
Key Findings
- •Increased β-END and ACTH concentrations were significantly associated with haircoat abnormalities (P < 0.001), while cortisol was not associated with any clinical signs.
- •Advanced age was independently associated with muscle atrophy, weight loss, and lethargy (P < 0.001), distinct from PPID-related signs.
- •β-END concentrations were 5-fold higher in PPID horses (median 291 pg/mL) compared to geriatric controls (median 55 pg/mL; P < 0.001).
- •Clinical distinction is essential: haircoat abnormalities indicate PPID pathology, while muscle wasting and lethargy may reflect age rather than endocrine dysfunction.