Eosinophilic granuloma (EG) is the most common benign form of Langerhans cell histiocytosis (LCH). Initially described by Lichtenstein in 1953, LCH encompasses a triad of proliferative granulomatous disorders primarily affecting children: EG, Hand-Schüller-Christian disease, and Letterer-Siwe disease.1 Lichtenstein first termed the disease histiocytosis X, after recognizing that the 3 syndromes had the same histology.1 The term was updated after the clonal proliferation of Langerhans cells in the pathogenesis of the disease was discovered.
As LCH is generally considered a pediatric disease, there is little in the literature regarding adult-onset LCH. The incidence of LCH in adults is reported as 1 to 2 cases per million, significantly lower than that in children.2,3 Two studies have reported the mean age at diagnosis in adults as the fourth decade of life, and have suggested a male predominance.4,5 The vast majority of adult LCH cases described are simple EG, with very few cases of multisystem disseminated disease reported.5
Adult patients with LCH typically present with solitary lesions in bone. Approximately 10% of cases have extraosseous involvement, with the lung being the most common site.6 Lesions tend to be unifocal, with fewer than 10 reports describing multifocal EG.1,7-13 The axial skeleton is most frequently involved, with the majority of lesions occurring in the skull, ribs, vertebrae, or mandible.14 While less common, the femur, humerus, and clavicle are most often involved when the appendicular skeleton is affected.5
In a literature review, a few case reports describe adult-onset EG of the skull. Only 5 case reports since the 1970s describe adult patients with EG of the femur. We present a rare case of multifocal EG in a 48-year-old woman with lesions of the femur and skull, as well as a review of the literature. The patient provided written informed consent for print and electronic publication of this case report.
Case Report
A 48-year-old woman presented with progressive right knee pain that was exacerbated by weight-bearing. She denied trauma, fevers, fatigue, or weight change. Her history was significant for an EG of the skull, excised at an outside institution 2 years prior to presentation. The patient also admitted to recent onset of right-sided skull pain, near the region of her previous surgery.
Physical examination demonstrated tenderness to palpation and fullness over the right medial distal femur and a normal neurovascular examination of the right lower extremity. Radiographs of the knee showed a cortically based, lytic, destructive lesion involving the medial femoral condyle, with soft-tissue extension (Figures 1A, 1B). Magnetic resonance imaging (MRI) of the right knee showed the lesion, with extraosseous soft-tissue extension (Figures 2A, 2B). The mass was isointense to muscle on T1-weighted images and hyperintense on T2-weighted images. Technetium bone scanning showed increased uptake in the right femur and the right skull (Figures 3A, 3B). MRI of the brain confirmed a new lesion in the right diploic space, distinct from the previous EG lesion site (Figures 4A-4D). An ultrasound-guided biopsy of the femur was performed and was consistent with EG.
After reevaluation and clearance by her neurosurgeon, the patient underwent curettage and allografting of the femoral lesion, with prophylactic internal fixation using a titanium distal femoral locking plate (Figure 5). Intraoperative frozen section was consistent with EG, which was confirmed with additional immunohistochemical workup (Figures 6A-6D).
The patient recovered uneventfully and follow-up radiographs showed restoration of the bony cortex of the medial femoral condyle (Figure 7). The second skull lesion, which was also consistent with EG, was excised by her neurosurgeon.
The patient remained asymptomatic until 2 years later, when she began experiencing mild pain in her right distal thigh and knee. Radiographs showed a new lytic focus in the right distal metadiaphysis (Figure 8) which was not present on her last radiograph 6 months prior. A computed tomography (CT) scan showed a lytic lesion involving the right distal femur medullary canal with cortical thinning and destruction, most pronounced posteriorly (Figures 9A, 9B). There was also an extraosseous soft-tissue component to the lesion. Bone scan showed increased uptake in the area of the new lesion. There was no increased uptake elsewhere, including the medial distal femur at the site of the old lesion, to suggest other lesions, and no increased uptake in the skull.
Given that the location of the lesion was distinct from the prior site of curettage and bone grafting, it was thought to be consistent with a new EG lesion. The patient underwent CT-guided biopsy, with simultaneous intralesional corticosteroid injection to treat the lesion when on-site pathology confirmed the etiology. Further surgical management was deemed unnecessary because internal fixation was present and spanned the new lesion. Final analysis of the fine-needle aspirate of the new lesion was positive for numerous eosinophils and histiocytes, consistent with EG.