Histopathology of insulin-induced laminitis in ponies

Abstract

Reasons for performing study: Ponies with laminitis associatedwith insulin resistance and hyperinsulinaemia lack systemicand/or intestinal inflammatory signs, suggesting a differentpathogenesis potentially reflected in differing histopathology.Objectives: To describe the histological appearance andquantify morphological changes in primary and secondaryepidermal lamellae (PEL and SEL) of laminitis lesions fromponies with insulin-induced laminitis.Methods: Equine hoof lamellar tissue was obtained from 4control ponies and 5 ponies with laminitis induced followinginfusion of insulin (1036 ± 55 mU/ml) while maintainingeuglycaemia for 55.4 ± 5.5 h. Sections from all 4 hooves werestained and examined by a veterinary pathologist.Measurements of lamellar length (PEL and SEL) were madein mid-dorsal sections of the right forefeet by 2 blindedobservers. Immunolabelling for calprotectin was performedusing a monoclonal antibody.Results: No lesions were detected in normal ponies. Lesionsdetected in ponies with laminitis were variable in severitybetween ponies.Within ponies, SEL lesions were more severealong the axial region of PEL. Lesions included swelling,disorganisation and abnormal keratinisation of epidermalcells, increased mitotic activity and apoptosis. Separation ofbasement membranes wasminimal. Immunostaining revealedinflammatory cells within the lamellar dermis. SEL weresignificantly elongated in laminitic hooves relative to controls,with the greatest elongation in those attached to abaxial andmiddle regions of PEL.Conclusions: Laminitis induced by prolonged infusion of insulinlacked widespread basement membrane disintegration, andincreases in epidermal cellular proliferation at axial aspectswere marked for this acute stage of disease.Potential releVance: Defining equine laminitis entirely interms of separation of the basement membrane may not beappropriate for laminitis associated with hyperinsulinaemia. © 2010 EVJ Ltd.