Histological and dermatoscopic description of sphynx cat skin

Background Histological and hair coat abnormalities of the alopecic sphynx cat have not been described in detail. The hairless allele (hr) in sphynx cats represents a mutation in the gene for keratin71, a protein expressed in the inner root sheath of humans and mice. Hypothesis/Objectives To describe the histological and dermatoscopic abnormalities of sphynx cat skin. Animals Skin biopsies were collected from 14 sphynx cats and five cats with normal coats. Dermatoscopic examinations were performed on 11 sphynx cats and six additional control cats. Methods Vertical and horizontal sections of skin biopsy samples from sphynx and control cats were reviewed. Dermatoscopic images were compared between sphynx and control cats. Results Sphynx cat hair follicles were often small, curved and kinked and demonstrated infundibular hyperkeratosis and dilatation. Changes in the inner root sheath of sphynx cats included a poorly defined Henle's layer in addition to vacuolar-like changes and eosinophilic globules in Huxley's layer. Dermal papillae in sphynx cat anagen bulbs lacked the normal flame shape and were surrounded by epithelial cells arranged in a disorderly manner. The degree of follicular abnormalities varied between follicles. Follicular density was similar for both sphynx cats and control animals. Sphynx cat hair shafts were misshapen, smaller in diameter and rarely medullated. Dermatoscopy revealed similar hair coat density in sphynx and control cats. Conclusions and clinical importance Sphynx cats demonstrated hair follicle dysplasia, with abnormal shaft production but without a decrease in follicle quantity. Abnormalities in sphynx cat follicles are similar to those in murine KRT71 mutants and suggest abnormal hair shaft keratinization.