CD1a-positive dendritic cell-enriched pigmented purpuric dermatosis in association with dyslipidemia

Indeterminate cells (ICs) are dendritic cells (DCs) that share the histologic features of Langerhans cells and macrophages but lack Birbeck granules. It remains unclear whether IC histiocytosis is a separate disease entity or a reactive process. We report the case of a male with an 8-year history of dyslipidemia who developed extensive pigmented purpuric papules. Laboratory studies revealed peripheral monocytosis (8.2%), and two skin biopsies showed a dermal lichenoid lymphohistiocytic infiltrate composed of CD4+ T cells and CD8+ T cells and CD68+CD163+CD1a+Langerin histiocytes. PD-1/PD-L1+T cells were present in the dermis. Our case may help in understanding the pathogenesis of IC histiocytosis, and we hypothesize that expression of CD1a+ dermal DCs and T-cell dysfunction is a reactive process to dyslipidemia.