Pathological fractures revealing Langerhans cell histiocytosis in an elderly female: a rare case report.

Introduction and importance: Langerhans cell histiocytosis (LCH) is a rare clonal proliferative disorder of dendritic cells, predominantly affecting children. Adult-onset LCH is uncommon and often misdiagnosed due to its atypical presentation. Pathological fractures as the initial manifestation are particularly rare in older adults. Case presentation: We report a 63-year-old female who sustained a pathological femoral fracture following minor trauma, with radiographs revealing cortical thinning and lytic changes. Subsequent imaging demonstrated multifocal osseous lesions involving the pelvis, vertebrae, and long bones. Histopathology confirmed LCH by characteristic morphology with immunohistochemical positivity for CD1a, S100, CD45, and Langerin (CD207). The femoral fracture was stabilized with intramedullary interlocking (IMIL) nailing after biopsy of the lesion. Two months later, she sustained a pathological humeral fracture with similar radiological features, which was managed with IMIL nailing without repeat biopsy because the lesion was considered clinically and radiologically consistent with the previously confirmed diagnosis of LCH. Systemic therapy with cytarabine and prednisolone was initiated for single-system multifocal osseous LCH. Clinical discussion: This case highlights the importance of considering LCH in the differential diagnosis of pathological fractures in adults, despite its rarity in the elderly. The occurrence of sequential pathological fractures of two long bones illustrates the aggressive skeletal manifestations that may occur in adult single-system multifocal LCH. Histological confirmation with immunohistochemistry remains the diagnostic gold standard. Surgical stabilization with IMIL nailing provided stable fixation, allowing early rehabilitation while systemic therapy was initiated for progressive multifocal skeletal disease. Conclusion: Adult-onset multifocal skeletal LCH should be considered in patients presenting with pathological fractures after low-energy trauma. Early histological diagnosis, multidisciplinary management, appropriate fracture stabilization, and timely systemic therapy may facilitate fracture healing and functional recovery. Longer follow-up with systemic imaging is required to determine long-term disease control.