Lamellar pathology in horses with pituitary pars intermedia dysfunction.
Authors: Karikoski N P, Patterson-Kane J C, Singer E R, McFarlane D, McGowan C M
Journal: Equine veterinary journal
Summary
# Editorial Summary: Lamellar pathology in horses with pituitary pars intermedia dysfunction Pituitary pars intermedia dysfunction (PPID) is a well-recognised endocrine disease affecting older horses, yet the specific pathological changes occurring within the hoof lamellae of affected animals had remained undescribed until this 2016 investigation. Researchers compared post-mortem hoof tissue from 16 PPID horses (six with concurrent laminitis, ten without) against ten age- and breed-matched controls, performing detailed histomorphometric analysis of primary and secondary epidermal lamellae whilst measuring fasting insulin, adrenocorticotropin and glucose levels. All PPID animals presenting with clinical laminitis showed marked hyperinsulinaemia (median 74.1 miu/l versus <20 miu/l in PPID cases without laminitis), and these hyperinsulinaemic horses displayed characteristic lamellar pathology including increased lamellae length and width, abnormal keratinisation, interlamellar bridging and tissue tearing—predominantly in the abaxial region—regardless of whether laminitis had been present for two months or five years; notably, lamellae from PPID horses without hyperinsulinaemia appeared structurally normal. This finding suggests that hyperinsulinaemia, rather than PPID per se, may be the critical pathogenic factor driving lamellar damage, with significant implications for practitioners: insulin dysregulation warrants aggressive dietary and metabolic management in all PPID cases, not merely those presenting with overt laminitis, and fasting insulin measurement should inform both diagnosis and preventive intervention strategies.
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Practical Takeaways
- •Horses with PPID and clinical laminitis show consistent lamellar damage; screen fasting insulin in these cases as hyperinsulinaemia appears to be the driving factor for tissue pathology
- •Normal insulin levels in PPID horses without laminitis suggests good metabolic control; absence of lamellar lesions in these cases indicates laminitis risk may be preventable with insulin management
- •Variability in lamellar lesion severity independent of laminitis duration suggests acute exacerbations may occur; monitor insulin status closely rather than relying on historical disease timeline
Key Findings
- •All PPID animals with laminitis had fasting hyperinsulinaemia (median 74.1 miu/l) whereas PPID animals without laminitis had normal insulin levels (<20 miu/l)
- •Lamellar pathology in PPID with laminitis included increased lamellae length/width, chronic abnormal keratinisation, interlamellar bridging, and cell death, predominantly located abaxially
- •Lamellar lesions in PPID with laminitis were variable in severity and unrelated to reported laminitis duration (2 months to 5 years)
- •PPID animals without laminitis showed normal lamellar morphology comparable to age and breed-matched controls, suggesting hyperinsulinaemia rather than PPID per se drives lamellar pathology