Track: Case Reports

Abstract:

Lymphocytic lobular panniculitis is a rare inflammatory disorder of subcutaneous fat, with atypical lymphocytic lobular panniculitides (ALLPs) representing a group of intermediate forms between lupus erythematosus panniculitis (LEP) and subcutaneous panniculitis-like T-cell lymphoma (SPTCL). A 24-year-old woman with a strong family history of lupus erythematosus presented with a 3-year history of recurrent painful subcutaneous nodules on proximal extremities, chest, breasts, abdomen, and buttocks/hips. She reported weight loss, oral ulcers, arthralgias, and night sweats. Biopsies showed dense lymphocytic infiltrates in subcutaneous adipose tissue with periadnexal extension, composed predominantly of small lymphocytes (CD8:CD4 ratio 2:1) admixed with plasma cells and histiocytes, scattered enlarged CD8-positive atypical lymphocytes, and areas of fat necrosis, increased mucin, and karyorrhexis. No monoclonal band was observed on T-cell gene rearrangement study. ANA was negative. CBC, CMP, LDH, and ferritin were within normal limits. Bone marrow biopsy and flow cytometry showed no morphologic or immunophenotypic evidence of marrow involvement. The overall diagnosis favors ALLP. Prednisone and hydroxychloroquine produced transient improvement, while methotrexate 10mg weekly led to rapid and complete resolution of nodules. Literature review shows that, unlike LEP, ALLPs rarely demonstrate fat lobule hyalinization, germinal centers, or mucin. Compared to SPTCL, ALLPs exhibit less lymphoid atypia, lower infiltrate density, and milder fat necrosis, with a lower CD4:CD8 ratio (1:2.9 vs. 1:5.2). Clinical courses of ALLPs may be indolent, relapsing, or progress to SPTC. Hence, recognizing the LEP-ALLPs-SPTCL spectrum is critical for guiding monitoring and therapy.

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