S100-negative indeterminate cell histiocytosis in an African American child responsive to narrowband ultraviolet B

Indeterminate cell histiocytosis is a rare cutaneous disease characterized by the presence of dendritic cells that lack Birbeck granules and immunophenotypically shares features of both Langerhans cells and macrophages. We describe a case of a 4-year-old African American boy affected by a disseminated, exclusively mucocutaneous form of indeterminate cell histiocytosis. The eruption was successfully treated with narrowband ultraviolet B. The peculiar negativity of the Langerhans cell marker S100 is also discussed.