[Fibrohistiocytic skin lesions]

A new unifying concept of fibrohistiocytic skin lesions.

Retrospective clinicopathologic study of more than 2,000 dermatofibromas (DF) recruited over the last two decades.

As the least common denominator all DF show a reactive fibrohistiocytic tissue response with variable epidermal hyperplasia, peripheral sclerosis and peripherally accentuated lymphohistiocytic tissue response. The histological, immunohistochemical and ultrastructural profile varies according to the time cycle as well as the fibro-myofibrohistiocytic differentiation of the lesions. From a conceptual point of view such lesions are best grouped into three categories: 1. DF with cellular/stromal pecularities. All classic variants, from the first description by Unna in 1894 to lesions described in 1978, namely DF, (benign) fibrous histiocytoma, histiocytoma cutis, sclerosing hemangioma, nodular subepidermal fibrosis or fibrous xanthoma, fall into this category; moreover, many of the clinicopathologic variants described over the last two decades such as granular cell, clear cell, myofibroblastic, sclerosing, monster cells, atypical ("pseudosarcomatous"), haemosiderotic ("elusive"), cholesterotic, and myxoid variants. 2. DF with architectural pecularities such as deep penetrating, atrophic, aneurysmal ("angiomatoid"), haemangiopericytoma-like, palisading and ossifying variants. And 3. DF with both cellular/stromal and architectural pecularities including those with a homogenous mixture of components as seen in epithelioid, cellular benign variants, smooth muscle proliferation in DF, multinucleate cell angiohistiocytoma, cellular neurothekeoma, and dermal plexiform fibrohistiocytic tumour; as well as those with heterogeneous mixture of components in composite or mixed dermatofibromas.

DF is common, the clinicopathological variability manyfold, and their misinterpretation as malignancy such as dermatofibrosarcoma protuberans or Kaposi sarcoma not rare. Such cases have important clinical implications such as unnecessary investigations, controls and livelong anxiety of patients.