Lamellar pathology in horses with pituitary pars intermedia dysfunction.

This study investigated the pathological changes in the hoof lamellar tissues of horses with Pituitary Pars Intermedia Dysfunction (PPID) that may or may not have concurrent laminitis, in comparison with age-matched controls. The results suggest that hyperinsulinaemia (abnormally high levels of insulin in the blood) may be associated with alterations and damage in the hoof lamellae indicative of laminitis.

Research Methodology

• The research study adopted a prospective case-control methodology.
• Hoof histological samples were obtained from the mid-dorsal sections post-mortem of 16 horses that had PPID. Some of these horses had concurrent laminitis (n=6) while others did not (n=10).
• An additional 10 similarly aged and bred horses without PPID were included as controls.
• All hoof sections were examined by a veterinary pathologist who was not privy to the information about the horses. Measurements of the length and width of 10 primary epidermal lamellae were taken using image analysis software.
• The morphology and any pathological variations of the primary and secondary epidermal lamellae were characterized and graded in different hoof regions.
• Prior to euthanasia, blood samples were taken from the horses to measure fasting serum insulin, plasma adrenocorticotropin, and blood glucose concentration.

Research Findings

• All the PPID horses which had laminitis also had abnormally high levels of insulin (hyperinsulinaemia), compared to PPID horses without laminitis, who had insulin within the reference range.
• In PPID horses with laminitis, the lamellar pathology varied in severity and did not correlate with the reported periods of laminitis. The abnormalities were mainly located at the furthest area of the lamellar tissue and involved abnormal lengthening and widening of the lamellae, abnormal buildup of keratin, the formation of cellular bridges between lamellae, and cellular death. In some cases, there were also more severe damages including lamellar tearing.
• The lamellae of PPID horses without laminitis showed no abnormalities compared to the control group.

Research Conclusion

• The study suggests that the PPID condition on its own and hyperinsulinaemia may not have a causal inter-relationship. Rather, the pathological changes consistent with laminitis in the hoof lamellae may be strongly associated with hyperinsulinaemia.