Macroscopic and microscopic features. Ill-defined alopecia in the cat trunk with multifocally grouped, 2 to 8 mm, pigmented, slightly raised, nonulcerated plaques (a). Detail of plaques arising from the alopecic and exfoliating skin (b): plaques have a rough surface and an irregular shape. Focal hyperplasia and dysplasia of the surface and follicular epidermis accompanied by mildly asynchronous keratinocyte maturation; note the loosely arranged and slightly fragmented collagen fibers in the dermis (c). Detail of (c): some keratinocytes have dark condensed nuclei and a clear cytoplasmic halo (koilocytes); others have a blue-grey cytoplasm (hematoxylin and eosin stain).