Proliferative and necrotising otitis in a kitten: first demonstration of T-cell-mediated apoptosis.

Otitis externa in cats is relatively uncommon. This report describes a case of a rare, visually distinctive, proliferative and necrotising otitis in a three-month-old Persian kitten. The cat had proliferative, erythematous and necrotic tissue covering most of the proximal pinnae and vertical ear canals. On histopathological examination, the most striking feature was the existence of scattered apoptotic-appearing keratinocytes within severely hyperplastic epithelium. For the first time, immunohistochemistry was used to show a closed association between CD3(+) T cells and caspase-3 stained keratinocytes, consistent with a keratinocyte apoptosis by epidermal-infiltrating T cells. Treatment was initiated using topical tacrolimus twice daily and an ear cleanser once daily. A marked improvement was observed after 10 days of treatment and the lesions completely resolved over a period of three weeks. The origin of T cells directed against keratinocytes is currently unknown.