RESUMO
BACKGROUND: Langerhans cell histiocytosis (LCH) is a rare clonal proliferative disease of Langerhans cells with unknown pathogenesis. An increasing number of clinicians recognize that LCH has a wide clinical spectrum and a highly varied course. Adults rarely develop LCH. Here, we report a case of adult localized LCH. CASE SUMMARY: A 32-year-old woman presented with plaques and ulcers on the vulva and crissum, accompanied by pain that persisted for more than one year. Physical examination revealed a red-infiltrating plaque with ulcerations and exudates in the vulva and crissum. Pathological examination revealed a diffuse infiltration of lymphocytes, eosinophilic granulocytes, and histiocytoid cells in the superficial dermis. Proliferative histiocytoid cells showed mild atypia, partly with kidney-shaped nuclei. Immunohistochemical examination showed that the histiocytoid cells were positive for S100 protein and CD1 and weakly positive for CD68 (20% +), with a Ki-67 index of 30%. Laboratory tests did not reveal any other systemic damage. The patient was diagnosed with adult localized LCH and was prescribed oral prednisone (20 mg) once daily. The skin lesions gradually improved and are still being followed-up. CONCLUSION: Adult localized LCH is rare and must be differentiated from other common conditions.