Author: Assoc Prof Patrick Emanuel, Dermatopathologist, Auckland, New Zealand, 2013.
Dermatomyofibroma was first described as a plaque-like dermal fibromatosis. It is a rare but distinct benigndermal proliferation of fibroblasts and myofibroblasts in the dermis.
Histology of dermatomyofibroma
Sections show an subtle, ill-defined, plaque-like dermal proliferation (figure 1). The cells are uniform, slender, spindle-shaped and bland. The cells contain evenly distributed chromatin or vesicular with small nucleoli and indentations is in keeping with a myofibroblastic line of differentiation. Characteristically, the cells are arranged parallel to the epidermis (figures 2, 3).
Immunohistochemically, neoplastic cells may express some actin and CD34 positivity. Elastic fibres are increased which can be demonstrated with elastic stains.
Differential diagnosis of dermatomyofibroma pathology
Immunohistochemical studies may be used to exclude other spindle cell lesions. The lack of an expression of S-100 excludes neurofibroma and desmoplastic spindle cell naevus. Lack of epithelial membrane antigen expression excludes perineurioma.
Mentzel T, Kutzner H. Dermatomyofibroma: clinicopathologic and immunohistochemical analysis of 56 cases and reappraisal of a rare and distinct cutaneous neoplasm. Am J Dermatopathol. 2009 Feb;31(1):44-9.
Weedon’s Skin Pathology (Third edition, 2010). David Weedon