Histologically, the epidermis was focally atrophic, and the dermis was increased in thickness, showing a spindle-cell proliferation that extended into the subcutaneous fat and included a reduction of cutaneous adnexa as well as a moderate collagenous component. A mild increase in perivascular mast cells was also noted.
Immunohistochemical findings included CD34 and factor XIIIa immunoreactivity in a majority of spindle cells, suggesting a dermal dendritic cell phenotype of the proliferating population. The immunoreactivity of S100 protein and CD68 was not significant. An orcein stain demonstrated that elastic fibers were diminished.