Solitary Diaphyseal Langerhans Cell Histiocytosis of Femur in an Infant - A Case Report.

Introduction: Langerhans cell histiocytosis (LCH) is a group of idiopathic disorders characterized by proliferation of bone marrow-derived Langerhans cells. It has a multitude of presentations - ranging from unifocal single system disorder to multisystem disorder. Most of these present in childhood; however, rare cases have been reported in adulthood as well. Case Report: Herein, 8 months old boy presented with refusal to weight bear on the right lower limb for 1 week. Mild elevation of C-reactive protein and white blood cell count. Plain Radiograph showed a lytic lesion in the femur with periosteal reaction. Magnetic resonance imaging showed a subperiosteal fluid collection suggestive and muscle inflammation. The patient was taken for curettage and biopsy of the lesion. Histopathology confirmed LCH, with positive for S100 (Histiolytic marker) and CD1a (Langerhan cell specific marker). Whole body positron emission tomography/Computed tomography confirmed a solitary lesion consistent with single system Unifocal bone LCH. Systemic therapy was initiated with the help of pediatric hematologist. Clinical and radiological outcome observed periodically. The patient was initially evaluated for osteomyelitis. However, we arrived at a diagnosis of LCH on the grounds of morphology and immunohistochemistry. Conclusion: This case highlights the importance of biopsy for diagnosing bone lesions in infants, as unifocal LCH can mimic osteomyelitis or malignancy. We reported a case of diaphyseal femur LCH in an infant, which has not been reported in the Indian literature until now.