Multifocal Langerhans cell histiocytosis in a child.

Langerhans Cell Histiocytosis (LCH) is a rare disorder sometimes called the disorder of the "monocyte-macrophage system". This condition is characterized by the proliferation of abnormal Langerhans cells within different tissues. Skin rash is the typical early feature, but bony involvement is the second most common presentation. The most common complications are musculoskeletal disabilities, hearing problems, skin scarring, neuropsychiatric defects and most importantly, progression to secondary malignancies like leukemia. Early recognition and treatment can reduce morbidity and mortality. Herein, we report a case of a 10-year-old male presenting with a tender, palpable mass in the lower limb. On initial imaging, a lesion involving the diaphysis of the fibula was observed, raising concerns of Ewing sarcoma. Biopsy was planned along with whole-body MRI, revealing multifocal single system Langerhans cell histiocytosis. Given the rarity of fibular involvement in LCH, distinguishing between LCH and common malignancies within this age-group can be challenging. Through this case report, we hope to emphasize the importance of considering LCH in the differential diagnosis to ensure a timely diagnosis, fitting treatment and improvement in prognosis of the condition.