Feline perforating dermatitis resembling human reactive perforating collagenosis: clinicopathological findings and outcome in four cases

The clinicopathological findings of perforating dermatitis in two young and two adult cats are described. In all cases, the lesions were characterized by single or multiple papules and plaques, 0.5–3.0 cm in diameter, each containing a central, firm, exophytic, cone-shaped, yellow-orange keratotic plug, tightly adherent to the underlying skin. Removal of the protruding material was associated with bleeding and left the ulcerated surface exposed. In one case, the lesions showed a linear configuration and identical lesions occurred on the suture sites following biopsy. Histopathologically, the diagnosis was straightforward because of the presence of vertically orientated collagen bundles extruded from ulcerated, concave-shaped invaginations of the skin. In two cases, vitamin C administration failed to resolve the disease. In two cases, methyl-prednisolone acetate was used to manage relapsing episodes and vitamin C helped to reduce glucocorticoid requirements. In one case, treatment with methyl-prednisolone acetate only appeared to be curative. The fourth case was lost to follow-up immediately after the diagnosis.