Subcutaneous Panniculitis-Like T-Cell Lymphoma With Granulomas as the Predominant Feature.

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare primary cutaneous lymphoma preferentially localized in the subcutaneous adipose tissue and composed of cytotoxic T cells with an α/β immunophenotype. The neoplastic T cells can be variably admixed with other inflammatory cells, including histiocytes, which can rarely form noncaseating granulomas. We present a case of SPTCL in which granulomas are the predominant feature, composing 75%-80% of the inflammatory infiltrate. The top differential diagnoses included infectious and autoimmune etiologies. However, special stains for microorganisms were negative, and immunohistochemical analysis of the atypical lymphocytes showed a CD3, CD8, TIA-1+, T-cell receptor (TCR) beta+, and CD4 infiltrate with a high Ki67 proliferation index of approximately 30%. TCR gene rearrangement studies by polymerase chain reaction with confirmation by high-throughput sequencing were necessary to exclude an autoimmune etiology, specifically lupus erythematosus panniculitis. To the best of our knowledge, only 1 other case of SPTCL with prominent granulomas has been reported in the literature. It is important for dermatopathologists to recognize this presentation of SPTCL. SPTCL with predominant granulomas should be included in the differential diagnosis of granulomatous panniculitis along with infectious and autoimmune panniculitides as well as other granulomatous lymphomas.