Development of dermatomyofibroma in a male infant.

Dermatomyofibroma is a rare benign cutaneous mesenchymal neoplasm of the fibroblasts and myofibroblasts. The majority of dermatomyofibromas present as red-brown discolored plaques or nodules, commonly located on the shoulder, upper arm, axilla, neck, and/or upper trunk. These lesions develop most frequently in young female patients at a mean of 28-years-of-age. Herein, a case of dermatomyofibroma is reported that developed in an infant. A 4-month-old boy presented with an ill-defined bluish firm plaque on the trunk that developed 1 month after birth. Histopathologically, there was proliferation of bland-looking spindle cells with fascicular arrangement in the dermis and subcutaneous tissue. Immunohistochemistry showed that most of the tumor cells expressed diffuse positivity for vimentin and smooth muscle actin, but were negative for S-100 protein, desmin, and CD34.