Cutaneous focal mucinosis--a histopathological and immunohistochemical analysis of 11 cases.

The histogenesis of cutaneous focal mucinosis (CFM) is controversial. Eleven cases of CFM (5F, 6M; mean age 51 years) from our routine files between 1986 and the present time have, therefore, been examined histopathologically and immunohistochemically. Histology revealed an increased number of fibroblast-like cells in early lesions, whereas they were diminished or predominantly at the margin in advanced ones. The myxomatous areas showed slight to absent reticulum formation. Similarly, elastic fibers were almost absent, and collagen fibers were fragmented and replaced by variable amounts of mucin. One specimen revealed an epithelial component within the lesion reminiscent of a poorly induced trichofolliculoma. Immunohistochemically, vimentin was consistently present and correlated with the number of fibroblast-like cells. A few (< 5%) CD34+ dermal dendritic cells (DDs) were focally seen within CFM. In contrast, FXIIIa+ DDs accounted for up to 30%. Fibroblast-like cells were negative for S-100 protein, Leu7, desmin and alpha-SMA. The epithelial component within one of our specimens seems to have been induced by CFM and is a feature also seen in (angio)-myxomas. CFM appears to be a mesenchymally derived lesion composed predominantly of fibroblasts. DDs do not form the major cell component but rather seem passively incorporated.