Light-chain-restricted plasmacellular infiltrates in necrobiosis lipoidica - A clue to an underlying monoclonal gammopathy

Background: Necrobiosis lipoidica (NL) is a member of the palisading granulomatous dermatitides that is associated, in most cases, with diabetes mellitus. However, there are an increasing number of cases of NL associated with other forms of systemic disease. We describe a novel case of NL associated with a light-chain-restricted plasmacellular infiltrate; subsequent investigations established an underlying monoclonal gammopathy. Methods: Skin biopsy material was obtained and was processed in the usual fashion for hematoxylin and eosin (H&E) examination. Immunohistochemical staining was performed by utilizing kappa and lambda monoclonal antibodies (Dako Corporation, Carpentiera, CA, USA). Kappa and lambda in situ hybridization was also performed (Ventana Medical Systems, Tucson, AZ, USA). Results: A 55-year-old woman with a 5-year history of bilateral thigh subcutaneous nodules underwent a skin biopsy, showing typical changes of NL; there was a concomitant prominent perivascular plasmacellular infiltrate. Kappa light chain restriction was observed amid the plasmacellular infiltrate. Bone marrow biopsy and immunophenotyping studies revealed a clonal plasmacytosis with kappa light chain restriction. Conclusions: Granulomatous inflammation, including NL, may be a cutaneous paraneoplastic expression of low-grade B-cell lymphoproliferative disease in the context of an underlying plasma cell dyscrasia.