Solitary nodule of cutaneous reticulohistiocytosis: A case report

Introduction: Solitary cutaneous reticulohistiocytosis represents a rare form of benign monocyte/macrophage proliferation. On routine histology, these lesions are typically described as large cells with cytoplasm showing ground glass appearance and giant cells. They grow up to 1 cm in size with rare cases exceeding this size. Case Report: This case report of a 28-year-old male demonstrated a nodule of reticulohistiocytosis measuring 2.2 cm in size. Microscopic features showed a well-demarcated nodule in the dermis with large histiocytes with ground-glass eosinophilic cytoplasm, giant cells, and foamy macrophages in a background of mixed inflammatory cells. Immunohistochemical staining showed positive staining for vimentin, CD68, CD31, with focal and patchy positivity for S100, CD43, and CD45 and negative staining for CD1a, langerin, CD21, CD23, CD30, CD34, ERG, D2-40, AE1/AE3, epithelial membrane antigen (EMA), smooth muscle actin (SMA), myogenin, desmin, SOX10, HMB-45, tyrosinase, and MelanA. Conclusion: The microscopic and immunohistochemical findings are characteristic of this entity but it is important to recognize for proper management and differentiation from other malignant lesions.