Routine hematoxylin-eosin staining of the biopsy specimen revealed an unremarkable epidermis. In the dermis, there was a mild to moderate perivascular mononuclear cell infiltrate. Giemsa stain revealed the infiltrate to be predominantly composed of mast cells.
Mastocytosis results from an abnormal proliferation of mast cells. Cutaneous mastocytosis, also known as urticaria pigmentosa, usually appears as diffuse pigmented papules. Involvement of the skin folds is infrequently found. A case of inguinal mastocytosis composed of pigmented papules that demonstrated a Darier sign has been previously reported. Histologic analysis in that case, however, demonstrated a Langerhans cell infiltrate associated with the mast cells.1 Therefore, the diagnosis of mastocytosis remains in question. A mast cell–rich variant of Langerhans cell histiocytosis with urticating lesions has been previously reported.2
Inguinal Pigmented Papules. Arch Dermatol. 1999;135(2):203-c-208. doi:10-1001/pubs.Arch Dermatol.-ISSN-0003-987x-135-2-dof0299