Atypical decubital fibroplasia with unusual histology

A case of atypical decubital fibroplasia with unusual histology arising in the buttock of a 68-year-old bed-ridden male in presented. The lesion measuring 5.4 cm in greatest dimension was histologically characterized by a proliferation of fibroblasts with oval to spindle nuclei and dense fibrous stroma with focal hyalinization and calcification. Ganglion-like fibroblastic cells and multinucleated giant cells of osteoclast type were also observed. There were numerous elastic fibers within and adjacent to the proliferating stromal cells. The proliferating stromal cells were positive for vimentin and collagen type IV but negative for CAM 5.2, epithelial membrane antigen, desmin, alpha-smooth muscle actin, muscle actin, HHF35, S-100 protein and CD34. Ultrastructurally, they were of a fibroblastic nature. The hypercellularity, lack of zones of fibrinoid necrosis, lack of lobulation and the presence of multinucleated giant cells were different from the originally described lesion. This condition represents a variant of atypical decubital fibroplasia. Pathogenic factors of this lesion are considered to be chronically repeated pressure and associated intermittent ischemia. The recognition of the lesion and its distinction from a sarcoma is essential.