Langerhans Cell Histiocytosis Presenting As Painful Tibial Swelling in a 6-Year-Old Child: A Diagnostic Pitfall Mimicking Osteomyelitis and Ewing Sarcoma

Sir, Langerhans cell histiocytosis (LCH) is a clonal myeloid neoplasm characterized by expansion of CD1a+/CD207+dendritic cells and a highly variable clinical spectrum from solitary bone lesions to multisystem disease. The bone is the most commonly affected organ in children. Among bones, the skull is the most common site. Long bones such as the femur and tibia are also frequent sites. High-quality epidemiologic data from South Asia (incidence, site distribution, outcomes) are sparse; most large cohorts are from Western centers. Reporting regional cases would help define local disease patterns and inform resource-appropriate guidelines. We report a 6-year-old male child who presented initially to a civil hospital with pain and swelling over the right leg for 1 month. The pain was insidious in onset, progressive, and localized to the middle third of the tibia, worsening on exertion. There was no history of trauma or fever. On examination, there was a 4 cm × 4 cm tender swelling over the right leg. There was no neurovascular deficit. X-ray [Figure 1] of the right leg showed a lytic area suggestive of osteomyelitis with periosteal reaction and ? sequestrum. Magnetic resonance imaging of the leg [Figure 2] done was suggestive of chronic osteomyelitis ? Ewing’s sarcoma. The patient was started on intravenous antibiotics. Patient reported to this hospital, and he was taken up for immediate debridement and biopsy. Intraoperatively, there was a 5 mm × 5 mm defect on the anteromedial aspect of the tibial shaft [Figure 3]. Biopsy revealed sheets of histiocytes with coffee-bean nuclei, scattered multinucleated giant cells, and an eosinophil-rich inflammatory background [Figure 4]. There was no marked atypia, mitosis, or necrosis. Immunohistochemistry showed strong positivity for S100 [Figure 5], CD68 [Figure 6], and cyclin D1 [Figure 7].Figure 1: Lateral view of right leg showing lytic area with ? periosteal reactionFigure 2: Magnetic resonance imaging-short TI inversion recovery coronal image of the right leg showing an enhancing, well-defined lesion in the right tibiaFigure 3: Intraoperative image showing a 5 mm × 5 mm defect in the anteromedial aspect of the right tibial shaftFigure 4: Eosinophil-rich inflammatory infiltrates (red) with multinucleate giant cells and coffee bean-like histiocytes (black) (Hematoxylin and Eosin, ×400)Figure 5: S100 highlighting langerhans cells (immunohistochemistry, ×400)Figure 6: CD68 positivity highlighting macrophages and histiocytes (Immunohistochemistry, ×400)Figure 7: Cyclin D1 showing nuclear positivity in neoplastic Langerhans cells (Immunohistochemistry, ×400)The case was diagnosed as a case of LCH, right tibia, and IHC for CD1a was outsourced which was reported as positive. Review of the outside images by the radiologist at our center showed the lytic lesion to be relatively well defined with punched-out margins with minimal soft-tissue component and homogenous enhancement of the lesion. These features should prompt an additional differential of LCH on imaging in such cases, especially considering the age of the patient. The patient was planned for intralesional corticosteroid therapy. However, on imaging, no residual lesion was found, so the patient was put on 3-monthly follow-up and was given no further treatment. The patient is asymptomatic with no pain at 6 months postinitial biopsy. This case highlights that LCH of long bones can closely mimic chronic osteomyelitis and primary bone malignancies such as Ewing sarcoma clinically and on imaging, particularly when periosteal reaction and cortical destruction are present. Timely biopsy, awareness, and suspicion of LCH in such cases are therefore essential. The most frequently affected bones are the skull (34%), spine (15%), ribs (7%), and long bones (15%) with the diaphysis being the most commonly involved region in long bones (58%), followed by the metaphysis[1] Singh et al.[1] reported a similar case as ours in an 8-year-old female child with the site of lesion being the tibia, and also mimicry on imaging with osteomyelitis McCarville et al.[2] emphasized that osteomyelitis and LCH are among the most common benign mimics of pediatric bone malignancy and that clinical and imaging overlap is frequent; the study recommends biopsy when imaging and clinical features are ambiguous. Khung et al.[3] (skeletal LCH review) reported that unifocal bone involvement is common and that long bones (femur, humerus, and tibia) are typical sites, consistent with our case Ezeokoli et al.[4] described outcomes of unifocal and multifocal osseous LCH in children, reinforcing that unifocal lesions generally have an excellent prognosis when appropriately recognized and managed. Nuclear cyclin D1 is consistently expressed in LCH. This occurs because BRAF V600E mutation activates the mitogen-activated protein kinase pathway, leading to cyclin D1 overexpression.[5] For unifocal, single-system LCH with classic morphology and immunophenotype, as was in our case, many argue that molecular testing may be optional, not obligatory. The variable frequency of BRAF V600E mutation (not 100% of cases) underscores that the absence of a mutation does not rule out LCH.[6] LCH is a rare cause of a solitary lytic lesion in children. The radiological and clinical findings may often be vague. The gold standard for diagnosis is biopsy. Management with curettage and intralesional methylprednisolone injection can lead to complete resolution of the lesion with minimal chance of recurrence. Success in diagnosis hinges on a high degree of suspicion.[7] It is important to differentiate LCH from conditions such as osteomyelitis and Ewing’s sarcoma, as the management strategies and prognostic outcomes for these conditions differ significantly, with substantial implications on the patient’s management and overall prognosis. The importance of histopathology and high index of suspicion is pertinent. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.