Dermatofibroma with diffuse eosinophilic infiltrate.

Dermatofibroma, a common form of benign fibrous histiocytoma, is characterized by the presence of different cell types consisting of fibroblastic, histiocytic, and even multinucleated cells. Dermatofibromas are always accompanied by an inflammatory lymphoid cell reaction, including B cells and T cells at their border. To our knowledge, however, there is no report of an infiltration of eosinophils within this tumor. We describe a dermatofibroma on the pretibial region of an 8-year-old boy. Microscopic examination revealed a diffuse eosinophilic infiltration within the dermatofibroma, which was typically composed of histiocytic cells and mature collagen. The diagnosis of dermatofibroma was confirmed by demonstrating the immunoreactivity of tumor cells to an anti-factor XIIIa antibody.