Abstract

INTRODUCTION

Xanthogranulomatous inflammation is a rare chronic inflammatory process characterized by the presence of histiocytes, foamy macrophages, and activated plasma cells [1]. This condition has been identified in various organs, including the salivary glands, gallbladder, kidneys, and gastrointestinal tract [2,3]. Xanthogranulomatous osteomyelitis (XO) is an uncommon and chronic inflammatory disease of the bone, marked by the accumulation of cholesterol-laden foamy macrophages, histiocytes, and plasma cells [4]. Delayed-type hypersensitivity reactions of cell-mediated immunity may contribute to the pathogenesis of this condition [5]. XO can present with nonspecific inflammatory symptoms, and its potential to mimic conditions such as Langerhans cell histiocytosis, chronic recurrent multifocal osteomyelitis, and Erdheim-Chester disease can complicate its diagnosis [1,6]. The lesions associated with XO are particularly challenging to diagnose because they can resemble malignancies on both imaging studies and pathological examinations [7]. In this report, we describe a rare case of XO that was diagnosed following renal transplantation and was initially mistaken for malignancy.

CASE REPORT

This study adhered to the principles outlined in the Declaration of Helsinki and was approved by the Institutional Review Board of Chosun University Hospital (IRB No. CHOSUN 2023-12-025). Informed consent was waived due to the retrospective nature of the study.

A 41-year-old man presented to the Department of Nephrology with a palpable mass on the anterior chest wall, first identified approximately 2 weeks before admission. He had undergone a deceased donor kidney transplant for diabetic kidney disease 4 years earlier and was on a regimen of immunosuppressive medications, including prednisolone (5 mg), tacrolimus, and mycophenolate mofetil. Laboratory tests revealed a white blood cell count of 11,260 cells/µL (reference range, 4,400–10,000 cells/µL), an elevated erythrocyte sedimentation rate of 88 mm/hr (reference range, 0–15 mm/hr), a C-reactive protein level of 10.5 mg/dL (reference range, 0–0.5 mg/dL), and a serum creatinine level of 1.27 mg/dL (reference range, 0.6–1.3 mg/dL). Serological tests for viral markers, including hepatitis B virus, hepatitis C virus, Epstein-Barr virus, human immunodeficiency virus, cytomegalovirus, and BK polyomavirus, were all negative. Subsequent imaging studies, including computed tomography (CT) and bone scans, were conducted. CT revealed a periosseous heterogeneously enhancing soft tissue mass measuring 7.8 × 4.2 cm, with an associated focal osteolytic bone lesion adjacent to the sternal end of the left clavicle. Additionally, irregular and destructive osteolytic bone lesions were noted on the left side of the sternal manubrium (Fig. 1A and B). The bone scan demonstrated increased uptake in the manubrium, left manubrioclavicular joint, and left first rib (Fig. 1C). These radiological findings raised suspicion of a malignant lesion, such as a sarcoma. Biopsy was performed to confirm the diagnosis, revealing fibro-collagenous tissue with dense histiocytic infiltration and diffuse infiltration of inflammatory cells, leading to a diagnosis of an inflammatory myofibroblastic tumor (IMT). The patient underwent complete surgical resection of the mass, including partial sections of the clavicle and sternum. Microscopic examination of the resected tissue showed foamy histiocytes with numerous lymphoplasmacytic cells. The diagnosis of XO was confirmed by a pathologist (Fig. 2). The resection procedure was successful in treating the XO, and the patient experienced no recurrence during the follow-up period.

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Fig. 1

(A, B) Computed tomography scans reveal a periosseous heterogeneously enhancing soft tissue mass (white arrows) adjacent to an exacerbated focal osteolytic bone lesion (blue arrows). (C) A bone scan indicates increased uptake in the manubrium, the left manubrioclavicular joint, and the left first rib (arrows).

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Fig. 2

Pathologic findings (H&E, ×10). (A) Light microscopy reveals a lesion primarily composed of foamy histiocytes, accompanied by a notable presence of lymphoplasmacytic cells. (B) Infiltration of adjacent skeletal muscle bundles (circled) by these cellular components is evident. (C) Additionally, focal areas of abscess formation and fibrinoid necrosis (arrowheads) are observed within the area.

DISCUSSION

To our knowledge, this is the first report of XO occurring after kidney transplantation. The initial reports of XO were published in 1984 [8]. XO is generally considered benign and treatable. However, it can mimic malignancy on radiological and gross examinations, resembling conditions such as osteosarcoma. While osteosarcoma presents with characteristic symptoms such as bone pain, swelling, and fractures [9], XO is associated with a delayed-type hypersensitivity reaction of cell-mediated immunity and is accompanied by systemic and regional clinical presentations, including pain, fever, and leukocytosis [10]. Due to its chronic inflammatory nature and potential to mimic neoplastic conditions, histopathological evaluation is crucial in cases of XO. Therefore, biopsy or surgical resection is essential for accurate diagnosis [11]. The radiological findings in our case were suggestive of sarcoma, whereas the needle biopsy findings revealed IMT, presenting spindle cell proliferation of uncertain histogenesis with a variable inflammatory component [7]. However, the final pathological examination of the excised mass revealed foamy histiocytes with numerous lymphoplasmacytic cells, confirming the diagnosis of XO.

Previous studies have demonstrated that XO is associated with trauma and infection [4,12]. XO has also been reported to occur concomitantly with conditions that compromise the immune system, such as inflammatory bowel disease [13]. In the present case, the patient underwent kidney transplantation and was treated with immunosuppressive agents. We hypothesize that an inappropriate immune response, induced by these immunosuppressants, may be implicated in the development of XO. Further investigation is warranted to validate this hypothesis. Additionally, no effective treatment approach for XO has yet been established. Most lesions are managed with surgical excision to differentiate them from malignancies [4,12]. To date, our patient has not experienced recurrence. Herein, we present a case of XO occurring after kidney transplantation, highlighting the importance of diligent monitoring and effective management of immunosuppressive therapies to mitigate the risk of complications and side effects.

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REFERENCES