PA11 Langerhans cell histiocytosis in twin girls: a case report

Abstract Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasm that most commonly affects skin but can affect other organs. The reported incidence is approximately 5 in 1 million children, with a slight male preponderance. It is extremely rare in twins, with fewer than 20 cases reported. We present a case of multisystem LCH presenting in 1-year-old monochorionic diamniotic twin girls. A 19-month-old twin girl was referred to dermatology with a rash on her scalp, abdomen and groin unresponsive to topical treatments. She was diagnosed with seborrhoeic dermatitis at 12 months and was treated for eczema on her torso in the community. She had recurrent discharge from her right ear treated with antibiotics. She was on laxatives as required due to abdominal fullness. She was admitted to hospital with pyrexia and being generally unwell. Her liver function tests were deranged. Prior to admission she was not on any regular medication and had no known medical conditions. On examination, on her scalp there was an erythematous rash with overlying thick yellow crust and scattered brown and red papules. On her central chest, abdomen and napkin area there were scattered erythematous papules, some coalescing into violaceous plaques. The possibility of LCH was raised and a skin biopsy confirmed the diagnosis. A diagnosis of risk-organ-positive multisystem LCH was made with involvement of bone marrow, liver, spleen, bone and lung. She was enrolled onto and commenced treatment as per the LCH-IV clinical trial. Incidentally the second twin was noted to have a similar rash, with a chronically discharging right ear. Examination revealed a similar, less extensive rash, on the chest, scalp and inguinal folds. She was diagnosed with risk-organ-negative multisystem LCH, with bone involvement following skin biopsy. Both twins’ LCH samples harboured the oncogenic variant of BRAF. Both twins have completed 12 months of chemotherapy and moved onto maintenance therapy. Here we present a rare case of twin girls with multisystem LCH. This case highlights the need for vigilance when treating patients who are twins for LCH. One proposed mechanism for the incidence of LCH in identical twins is transfer of clonal cells in utero, as demonstrated in acute lymphoblastic leukaemia. Examination of blood spots of the twins is being arranged for investigation.