Figure 2.

A: In the earlier stage the lesions are hyperplastic and exudative. The animal shows a thickened hairless with focal superficial ulcerations (A). As the lesions progress the ulcers become deeper and extensive and do not heal (B). Microscopically, the earlier stages are characterized by a hyperplastic epidermis skin with fibrotic dermis, which is associated with atrophic hair follicles that may develop cystic structures, and relatively hypertrophic sebaceous glands (C). The fibrosis reaches the skeletal muscle layer and the hypodermis, as shown in green by the trichrome staining (E). The absence of an inflammatory reaction is conspicuous at this stage. As the lesion becomes ulcerated and chronifies it develops a superficial layer of debris and fibrin (D), which lies on a more cellular fibrous tissue. Even at this stage the infiltration is mainly composed of histiocytes and neutrophils with scattered mast cells. Only a few lymphocytes and plasma cells are observed (Inset). The whole process is now embedded in a dense fibrotic tissue involving the whole thickness of the skin (F).