Lobular Panniculitis due to Borrelia burgdorferi Infection Mimicking Subcutaneous Panniculitis-Like T-Cell Lymphoma

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.

Lymphocytic panniculitis: an algorithmic approach to lymphocytes in subcutaneous tissue

The diagnosis of panniculitis is a relatively rare occurrence for many practising pathologists. The smaller subset of lymphocyte-predominant panniculitis is further complicated by the diagnostic consideration of T cell lymphoma involving the subcutaneous tissue, mimicking inflammatory causes of panniculitis. Accurate classification of the panniculitis is crucial to direct clinical management as treatment options may vary from non-medical therapy to immunosuppressive agents to aggressive chemotherapy. Many diseases show significant overlap in clinical and histological features, making the process of determining a specific diagnosis very challenging. However, with an adequate biopsy including skin and deep subcutaneous tissue, a collaborative effort between clinician and pathologist can often lead to a specific diagnosis. This review provides an algorithmic approach to the diagnosis of lymphocyte-predominant panniculitis, including entities of septal-predominant pattern panniculitis (erythema nodosum, deep necrobiosis lipoidica, morphea profunda and sclerosing panniculitis) and lobular-predominant pattern panniculitis (lupus erythematous panniculitis/lupus profundus, subcutaneous panniculitis-like T cell lymphoma, cutaneous γ-δ T cell lymphoma, Borrelia infection and cold panniculitis).