Subcutaneous Panniculitis-Like T-Cell Lymphoma With Increased γδ T Cells: A Potential Diagnostic Pitfall.

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare primary cutaneous T-cell lymphoma with adipotropism characterized by infiltration of CD8 + T cells exhibiting a cytotoxic and αβ phenotype. Although SPTCL is typically indolent, distinguishing it from more aggressive cutaneous lymphomas such as primary cutaneous γδ T-cell lymphoma is critical for accurate prognosis. We present a case of SPTCL in a 26-year-old Asian woman with a history of hemophagocytic lymphohistiocytosis, who presented with nonulcerated, erythematous patches and hyperpigmented nodules on her extremities and trunk persisting for 5 months. Biopsy specimens revealed an atypical lymphoid infiltrate with prominent adipotropism, predominantly comprising atypical medium-sized lymphocytes rimming the adipocytes. Immunophenotypically, the lesional lymphocytes were CD3+/CD4-/CD8+/CD7+ T cells expressing TIA1, granzyme B, and TCR βF1, while lacking CD30 and Epstein-Barr virus-encoded small RNA expression. Intriguingly, there was a markedly increased density of T cells expressing TCR δ, some surrounding adipocytes and appearing neoplastic. CD123 failed to reveal aggregates of plasmacytoid dendritic cells. Molecular analysis revealed monoclonal TCR β and γ gene rearrangements. Despite the elevated γδ T-cell population (20%-50% of the T cells), the overall clinical, histopathologic, and molecular findings, along with the absence of rapid disease progression, supported a diagnosis of SPTCL. Although increased densities of reactive γδ T-cells or γδ T-cell phenotypes in neoplastic cells are observed in various benign and malignant dermatologic conditions, the literature on this phenomenon-particularly in SPTCL-remains scarce. Our case highlights the importance of recognizing an increased γδ T-cell population in SPTCL to prevent misdiagnosis as a more aggressive lymphoma such as primary cutaneous γδ T-cell lymphoma, underscoring the need for thorough clinicopathologic correlation.