Dermatomyofibroma (Plaqueförmige Dermale Fibromatose)

We reported a patient with dermatomyofibroma and reviewed the literature to characterize the immunohistochemical features of dermatomyofibroma. A 25-year-old woman presented with an asymptomatic, well-circumscribed, red-brown plaque on the left posterior shoulder. Microscopic examination revealed a non-encapsulated but well-circumscribed tumor in the mid-dermis extending into the upper subcutaneous fatty tissue. The tumor was composed of faintly eosinophilic, thin, wavy collagen fibers arranged as intersecting fascicles with an arrangement predominantly parallel to the skin surface. Embedded among the wavy fibers, there were a fair number of nuclei that were elongated, vesicular, and uniform in size. Immunohistochemical studies using a peroxidase-antiperoxidase technique disclosed that the cytoplasm of the tumor cells was positive for muscle actin. The tumor cells were negative for alpha-smooth muscle actin, desmin, factor XIIIa, S-100 protein, and CD34. Clinical, histopathologic, and immunohistochemical analysis confirmed dermatomyofibroma.