Ultrastructural histochemistry of infantile digital fibromatosis.

A case of infantile digital fibromatosis was studied by light and electron microscopy histochemistry. Using two different acidic solutions of phosphotungstic acid at varying pHs, the round inclusions characteristic of this tumor were shown to have a high protein content with little or no carbohydrates. The histochemical reactivity of the inclusions was similar to that of the cytoplasmic microfibrils in the tumors cells and consistent with the idea that both the inclusions and the microfibrils represent actin. There is, however, no definite proof that the tumor cells are myofibroblasts. At the present time, this tumor should be viewed as a peculiar expression of deranged assembly or metabolism of filamentous proteins or both.