Langerhans Cell Histiocytosis Presenting as a Limp in a Child: A Case Report.

We report a case of multifocal Langerhans cell histiocytosis (LCH) in a previously healthy four-year-old male child who initially presented to the chiropractic clinic with a three-week history of progressive left-sided limping and nocturnal leg pain. Upon evaluation, the patient demonstrated an antalgic gait, point tenderness over the left femur and tibia, and constitutional symptoms including low-grade fevers, fatigue, and recent weight loss. Radiographic evaluation revealed multiple lesions in the left femur, tibia, and pelvis, with subsequent MRI confirming infiltrative lesions and a pathological fracture of the femoral neck. PET scan identified additional lesions in the skull, spine, and right humerus with no visceral involvement. Biopsy of the femoral lesion confirmed LCH with CD1a and CD207 (langerin) positivity and BRAF V600E mutation. The patient was classified as having multifocal bone disease without risk of organ involvement, and treatment was commenced with vinblastine and prednisone per standard protocol. This case highlights the importance of recognizing red flag symptoms in pediatric limping presentations, demonstrates the critical role played by non-oncology providers in early detection of serious pathology, and illustrates the characteristic radiographic and histopathological features of multifocal LCH. The case further emphasizes how recent advances in understanding LCH's molecular pathogenesis as a clonal neoplastic disorder driven by mitogen-activated protein kinase (MAPK) mutations have refined our approach to the diagnosis and treatment of this rare but significant pediatric condition.