case_images: PMC8244783_01
case_images: Clinical, radiological, and histological features of mixed Erdheim Chester Disease (ECD)/Rosai Dorfman Disease (RDD) histiocytosis. (A) Axial computed tomography (CT) of the patient demonstrating infiltration of peri-nephric fat defined as "hairy-kidney," highly suggestive of ECD after 4 weeks of corticosteroids for ITP. (B) Tissue guided biopsy of perinephric lesions consistent with Rosai-Dorfman disease histology as shown by multinucleated histiocytes with large nuclei, abundant cytoplasm and lesions of emperipolesis (arrows). Haematoxylin and eosin staining (HES), original magnification x400. Biopsy was performed 3 months after ITP diagnosis. (B') Same samples showing perinephric lesions consistent with Rosai-Dorfman disease histology as shown by multinucleated histiocytes with large nuclei, abundant cytoplasm, and lesions of emperipolesis (arrows). Haematoxylin and eosin staining (HES), original magnification x100. Biopsy was performed 3 months after ITP diagnosis. (C) Sample samples showing tissue infiltration with multinucleated histiocytes with CD163 expression on immunostaining (HES; immunohistochemistry, x400) consistent with Rosai-Dorfman disease. (D) Same sample showing a strong expression of S100 protein (brown staining) by the multinucleated histiocytes (HES; immunochemistry, x400) consistent with Rosai-Dorfman disease. (E) Same sample showing a strong expression of S100 protein (brown staining) by the multinucleated histiocytes (HES; immunochemistry, x400) consistent with Rosai-Dorfman disease. (F) Sagittal 18FDG-PET CT-scan showing radiotracer uptake before (upper image) and after (lower image) rituximab infusions. An intense radiotracer uptake on "hairy-kidney" and a low tracer uptake on the testis was observed before treatment.
case_images: fmed-08-678456-g0001.jpg
case_images: PMC8244783_01_fmed-08-678456-g0001.jpg
case_images: F1
case_images: CT scan due to elevated gamma globulin level at ITP diagnosis. CT scan showed bilateral peri-nephric fat infiltration without other abnormalities (Figure 1A). The perinephric tissue biopsy showed infiltration with histiocytes, lymphocytes, and plasma cells rich in IgG-4 (130/high-power fields, IgG-4/IgG ratio: 25%; Figures 1B,B'). Histiocytes were CD68+, S100+, and CD1a-, with large nuclei and abundant lesions of emperipolesis (Figures 1C-E). Bone marrow aspiration was consistent with peripheral thrombocytopenia, although NGS detected somatic variants in several genes (TET2, ASXL1, DNMT3A, JAK2). 18F-fluorodeoxyglucose PET-CT showed intense radiotracer uptake in peri-nephric fat fibrosis, mediastinal lymph nodes, and a low tracer uptake on the testis (Figure 1F). After a two-year follow-up, the patient is still on prednisone (5 mg/day) and considered in clinical, biological (platelet count at 286 G/L, IgG1 at 5.32 g/L, and IgG-4 at 0.033 g/L) and metabolic (Figure 1F) remission.