CPC14: A rare adult presentation of cutaneous Langerhans cell histiocytosis associated with acute transformation of myeloid leukaemia

Ahmed Zwain, Xavier Peer, Saleem Taibjee and Dimitra Koch

Dorset County Hospital, Dorchester, UK

Langerhans cell histiocytosis (LCH) is a rare condition with a peak incidence between the age of 1 and 4 years. However, LCH may exceptionally occur in adults, in whom the reported incidence is 1–2 per million annually. Previous reports suggest an association with myeloproliferative disease (Hwang Y-Y, Tsui P, Leung RYY, Kwong Y-L. Disseminated Langerhans cell histiocytosis associated with acute myeloid leukaemia: complete remission with daunorubicin and cytarabine. Ann Hematol 2013; 92: 267–8; Ghosn MG, Haddad AC, Nassar MN et al. Acute myeloid leukemia and Langerhans’ cell histiocytosis: multiple theories for an unusual presentation. Leuk Res 2010; 34: 406–8). A 90-year-old woman was admitted to our hospital with vomiting and loose stools. She had a background of hypertension and hypercholesterolemia. She was treated for dehydration and sepsis but was noted to have a persistently raised white cell count of 32 × 10⁹ cells L^–1. Blood film and flow cytometry indicated acute transformation of chronic myelomonocytic leukaemia. Dermatology opinion was sought after a striking rash was noted, comprising pruritic erythematous papules and nodules affecting the intertriginous areas of the axillae and the under surface of the breasts and groin areas, extending to the abdominal wall and legs, of reportedly 6 months’ duration. The initial differential diagnosis included psoriasis, eczema and lichen planus. A skin biopsy showed conspicuous histiocyte-like cells with epidermotropism within a mixed infiltrate. Immunohistochemistry demonstrated positive staining for S100, CD1a, Langerin (CD207) and BRAFV600E, confirming LCH. A proportion of the background cells stained for myeloperoxidase and lysozyme, indicating additional neutrophils and immature myeloid cells consistent with possible cutaneous spillover of leukaemic cells. We present this case to highlight a number of important aspects. The clinical morphology of LCH in adults can vary and pose a diagnostic challenge, closely mimicking an inflammatory dermatosis. BRAFV600E immunohistochemistry can be useful in discriminating a true clonal LCH from reactive Langerhans cell hyperplasia, the latter sometimes noted in inflammatory dermatoses or skin tumours, as well as to identify a potential therapeutic target with BRAF inhibitors. This is a further report that demonstrates the genuine association of LCH and myeloproliferative disease in adults. The latter could reflect clonal proliferation and divergent differentiation of a common progenitor cell.