Solitary cutaneous histiocytosis with granular cell changes: a morphological variant of reticulohistiocytoma?

We first report a case of granular cell histiocytosis occurring as a solitary polypoid lesion of the nipple in a 15-year-old girl. Histologically, the lesion was composed of a dermal population of medium- to large-sized, short spindle- to round- to epithelioid-shaped cells with eosinophilic cytoplasm containing numerous and small diastase-resistant periodic acid-Schiff (PAS) positive granules. No associated inflammatory cells were observed. Immunohistochemical studies, revealing immunoreactivity exclusively to vimentin and CD68, were consistent with their histiocytic profile. Based on clinical, morphological and immunohistochemical features, the diagnosis of 'solitary cutaneous histiocytosis with granular cell changes' was proposed. The absence of an inflammatory cell component, such as lymphocytes and leucocytes, along with no history of a previous trauma or medical treatment, suggest that the present lesion could fit into the morphological spectrum of the so-called solitary epithelioid histiocytoma, also known as reticulohistiocytoma. Alternatively, the possibility of a histiocytic reaction to unknown stimuli cannot be completely ruled out. Nevertheless, awareness of solitary cutaneous histiocytosis with granular cell changes is useful to avoid confusion with other dermal tumors, especially 'granular cell tumor' and 'dermal non-neural granular cell tumor'.