Infantile digital fibromatosis. Immunohistochemical and immunoelectron microscopic studies

A typical case of infantile digital fibromatosis (IDF) was studied with antibodies raised against actin, vimentin, desmin and several species of cytokeratin. Strong reactions were observed for desmin, cytokeratin and CK-5, and moderate reactions for vimentin and actin. The diagnostic intracytoplasmic inclusion bodies within the tumor cells were ultrastructurally composed of aggregations of dense microfilaments. Immunoelectron microscopy showed that these filament aggregations are positively stained with anti-actin antibody. From these results, we suggest that the large tumor cell of IDF is a myofibroblast and may originate from or differentiate toward vascular smooth muscle cells, because only this type of smooth muscle can coexpress desmin, vimentin and cytokeratin.