Introduction: Langerhans cell histiocytosis (LCH) is a rare disease characterized by accumulation of clonal dendritic cells in various organs. It can occur at any age, with peak incidence between 1-4 years of age.The diagnosis of LCH is based on histological examination with immunophenotyping: identification of characteristic cells and the presence of markers CD1a and/or CD207 (Langerine) on the surface of the lesional cells. Molecular pathology is also required to monitor treatment response and disease activity ( BRAF V600E mutation, mutations in MAPK genes).Method: We report the case of a 4-month-old male infant with a 2-day history of respiratory distress with minimal oxygen requirement, enlarged cervical lymph nodes, and a progressive purplish papule rash for over 3 months. Enlarged liver and spleen were also noted on clinical examination and his chest radiography showed increased diffuse alveolar-interstitial markings in the upper half of the lungs. His blood work showed hemolytic anemia, and mild leukocytosis and thrombocytosis.Results: Clinical suspicion of Langerhans cell histiocytosis was raised, and a skin biopsy confirmed the diagnosis based on the presence of Langerin and CD1a markers. The infant was later evaluated and had multiple osteolytic lesions on CT and radio-graphic scans. He was started on vinblastin and prednisone with rapid clinical improvement.Clinical course of LCH varies from single-system disease, limited to one organ like the skin or bone, to a rapidly progressive multi-system disease involving the lymph nodes, liver, spleen, bone marrow, lungs and pituitary gland, making its clinical presentation highly variable and requiring a high index of suspicion to consider the diagnosis, especially when involvement of the lungs affects less than 15 % of children with LCH.Conclusion: This case underlines the need for a multidisciplinary approach in diagnosing multi-system LCH in children and also the need to have a high index of clinical suspicion in order to begin adequate life-saving treatment.
