'Bizarre' rash: adult-onset cutaneous Langerhans cell histiocytosis.

To cite: Khoo ABS, Garioch J. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2016217904 DESCRIPTION A woman aged 80 years was admitted under the general physicians with a 2-week history of general malaise. She was referred to dermatology for an opinion on a rash which had been present for 6 months. Examination revealed an erythematous, keratotic and papular rash below her breasts (figure 1), in both axillae (figure 2), upper abdomen and lower back. The rash was asymptomatic. The patient had no previous history of skin disease. A 4 mm punch biopsy showed discrete collections of monocytoid and histiocytoid cells within the epidermis expressing S100, CD1a and focal variable Leucocyte Common Antigen (LCA)—features diagnostic of Langerhans cell histiocytosis (LCH). MRI of the head and CT imaging of her chest, abdomen and pelvis did not reveal any other focus of disease, and there were no lytic bone lesions. LCH is a rare disease involving clonal proliferation of dendritic cells. The incidence of LCH in adults is ∼1–2 cases per million with a mean age of onset of 33 years. Cutaneous LCH can mimic common dermatoses, and can be easily misdiagnosed. The typical lesions described are papular, rose yellow in colour and often scaly. When LCH presents in the intertriginous areas, it can be mistaken for eczema, psoriasis or intertrigo.