Abstract

Langerhans cell histiocytosis (LCH) is a neoplastic clonal proliferation of immature myeloid precursors occurring primarily in neonates and children that most classically affects bone but can impact any organ. Skin-limited disease is rare, comprising 5% of patients with LCH. Histologically, cutaneous LCH exhibits dense dermal infiltrate of histiocytes with reniform nuclei and positive immunostaining with anti-CD1a, anti-CD207, and S100. Although this condition classically presents as multiple erythematous to brown papules, nodules, or vesicles, cases of solitary LCH lesions have been increasingly reported, accounting for up to 25% of skin-limited LCH. A full-term, two-week-old female presented with a solitary erythematous-yellow indurated nodule with central crust on the right buttock present since birth. Prenatal course and delivery were uncomplicated; maternal history was unremarkable. Complete blood count and complete metabolic panel were within normal limits. Skeletal survey revealed no bony lesions, and abdominal ultrasound confirmed normal spleen size. Skin biopsy demonstrated a dense infiltrate of large cells with reniform nuclei and moderate cytoplasm which stained positively for anti-CD207, anti-CD1a, and S100. Abundant small predominantly CD3+ lymphocytes and scattered eosinophils were also observed. Thus, a diagnosis of LCH was made. This case highlights an uncommon presentation of skin-limited LCH, augmenting the catalogue of literature-reported solitary LCH lesions. While this patient’s findings were most consistent with the congenital self-healing reticulohistiocytosis form of LCH, a phenotype no longer recognized under a recently updated histiocytosis classification system, proper diagnosis and full evaluation are imperative in all LCH cases given the high prevalence of systemic involvement.