Diffuse Large B-Cell Lymphoma With the “Leopard Man” Appearance on ¹⁸F-FDG PET/CT

Abstract

Subcutaneous nodules and masses as the primary manifestation of diffuse large B-cell lymphoma are exceedingly rare. We present ¹⁸F-FDG PET/CT findings of multiple hypermetabolic nodules and masses distributed throughout the body, creating a characteristic “leopard man” appearance on the MIP image, in a 65-year-old man. An excisional biopsy of the right thigh mass confirmed the diagnosis of diffuse large B-cell lymphoma.

FIGURE 1.

A 65-year-old man presented with painless enlargement of masses in both thighs over 4 months and underwent an MRI to assess their extent and nature. Multiple subcutaneous (arrowheads) and femoral intramedullary (arrows) nodules and mass-like lesions were observed. These lesions showed low signal intensity on coronal T1-weighted images (A), intermediate-to-high signal on fat-suppressed coronal T2-weighted images (B), and moderate enhancement on contrast-enhanced coronal T1-weighted images (C), suggesting metastatic tumors. An excisional biopsy of the right thigh mass was performed. Hematoxylin and eosin staining showed diffusely distributed large lymphoid-like cells with prominent nucleoli and fibrous septa (D and E). Immunohistochemistry showed positivity for CD20 (F), CD10, BCL2, MUM1, and BCL6 (30%), with MYC expression at 20%, and a Ki67 proliferation index of 95% (G), confirming the diagnosis of the germinal center B-cell (GCB) subtype of diffuse large B-cell lymphoma (DLBCL).

FIGURE 2.

An ¹⁸F-FDG PET/CT scan was performed to assess the extent of the disease. The MIP image (A) revealed multiple hypermetabolic subcutaneous nodules and masses distributed across the trunk and limbs, creating a distinctive “leopard man” appearance. Subcutaneous nodules and masses (arrowheads) were observed in the left proximal upper extremity (B), chest (C), abdomen (D), and both thighs (E). FDG uptake was observed in the lymph nodes of the left cervical region, anterior mediastinum, left perirenal space, and right iliac fossa. FDG uptake was also observed in extranodal sites, including the spleen, thoracic (T7), and lumbar (L4) spinal canals, and the right seminal vesicle. Marked osteomedullary uptake was observed in the diaphyses of the humeri, femurs, and tibiae. The “leopard man” pattern on ¹⁸F-FDG PET/CT has been previously reported in various conditions, including cutaneous polyarteritis nodosa,1 nodular-type muscular sarcoidosis,2 sarcoidosis,3 granulomatous myositis,4 VEXAS syndrome,5 and subcutaneous panniculitis-like T-cell lymphoma.6 Similar imaging appearances may also be seen in disseminated fusariosis,7 extranodal NK/T-cell lymphoma extensively involving the skin and subcutaneous tissue,8 extensive cutaneous-mucosal and muscular involvement of gamma/delta cutaneous T-cell lymphoma,9 pancreatic cancer with rare cutaneous and muscle metastases,10 subcutaneous and muscle metastases from rectal adenocarcinoma,11 and numerous granulomatous panniculitis lesions.12 Although extensive subcutaneous involvement in DLBCL is rare, it is not classified as primary cutaneous lymphoma according to the 2018 World Health Organization–European Organisation for Research and Treatment of Cancer joint classification for primary cutaneous lymphomas. This classification defines 3 main types of primary cutaneous B-cell lymphomas: primary cutaneous marginal zone B-cell lymphoma, primary cutaneous follicle center lymphoma, and primary cutaneous large B-cell lymphoma, leg type.13 DLBCL-GCB is a subtype of non-Hodgkin lymphoma originating from germinal center B cells.14 The whole-body imaging capabilities of ¹⁸F-FDG PET/CT allow for the detection of unusual sites of involvement, including the subcutaneous tissue, spinal canal, visceral organs, and bone marrow. This comprehensive evaluation is crucial for accurate staging and the development of appropriate treatment strategies for DLBCL.