Histologic evaluation of the diversity of epidermal laminae in hooves of horses without clinical signs of laminitis

Objective-To evaluate the histologic diversity of epidermal laminae in hooves from horses without clinical signs of laminitis. Sample Population-Formalin-fixed samples of stratum internum obtained from the mid region of the dorsal aspect of the hoof wall from the forelimbs of 35 Thoroughbred cadavers (including foals [n = 9], yearlings [51, 2 year olds [61, racing horses [51, and mares [101). Procedures-Paraffin-embedded laminar tissues were stained with H&E for the evaluation of architectural variety of primary epidermal laminae (PEL) and secondary epidermal laminae (SEL). For detection of cytokeratin (CK) expression in epidermal laminae, immunohistochemical staining was performed by use of anti-CK14 and anti-CK8.12 antibodies. Results-The morphology of the PEL, SEL, and tips of PEL was classified into 3, 5, and 3 patterns respectively. Differences in the predominant type of SEL depended on their location with respect to the laminar interface. In SEL attached to the sides of PEL, the basal cells were immunoreactive to CK14 and CK8.12, which was interpreted as a normal pattern. In some SEL at the tips of PEL, the suprabasal cells expressed CK14, CK8.12, or both, which constituted a hyperplastic pattern. Conclusions and Clinical Relevance-The histologic diversity of epidermal laminae from hooves of Thoroughbreds was attributable to the combined morphology of PEL and SEL. Detection of hyperplastic changes in the laminar interface does not justify a diagnosis of laminitis because such changes can develop independent of clinical disease. The classification system used here should aid investigators in making a more accurate histologic evaluation of laminae. (Am J Vet Res 2009;70:186-193)