First case report of ultrastructural cutaneous abnormalities in equine atopic dermatitis

•Atopic dermatitis is characterized by skin barrier defects in people and dogs.•We report ultrastructural studies of skin barrier defects in atopic horses.•Detected changes are similar to what reported in other species.•Future studies are needed to confirm these preliminary findings.

Atopic dermatitis (AD) is a common skin disease that affects humans and animals. Skin impairment has been described in human and canine AD. Equine AD is recognized in practice but little is known about its pathogenesis. As remarkable similarities exist across species in terms of cutaneous manifestations of AD, it was speculated that skin abnormalities may also exist in atopic horses. This case report describes the ultrastructure of the stratum corneum of two normal and two atopic horses. Biopsies were taken from sites predisposed to AD and examined using electron microscopy. Stratum corneum in normal samples was compacted with organized lipid lamellae while in atopic samples disorganized lipid lamellae, retained lamellar bodies and amorphous lipids were found. These changes are very similar to what reported in AD in other species. It is currently unknown whether these abnormalities in atopic horses are primary or secondary and their importance in allergen penetration.