Histopathology of necrobiotic xanthogranuloma with paraproteinemia.

Fifty-three cutaneous biopsies from 22 patients with necrobiotic xanthogranuloma (NXG) were reviewed. One or more biopsies from each patient displayed a typical pattern of palisading histiocytic xanthogranuloma with bands of hyaline necrobiosis. Multiple foam cells and Touton giant cells were present, and atypical, bizarre-appearing foreign body giant cells were characteristic. Cholesterol clefts were found in 18 specimens, and lymphoid nodules were found in 24, 8 of which had germinal center formation. Twenty-one specimens contained foci of plasma cells, and these were located perivascularly, at the periphery of lymphoid nodules, and, as infiltrates, between dermal collagen bundles. Unique features were xanthogranulomatous panniculitis, often appearing as Touton cell panniculitis, and a rare but distinctive palisading cholesterol cleft granuloma. The cytoplasm of giant cells and histiocytes contained PAS-positive, diastase-resistant polysaccharide. Examination of 3 cases by electron microscopy revealed dendritic cells in the epidermis and vacuolated dermal histiocytes. S-100 antibody was negative in 3 cases. Leukocyte monoclonal antibody studies in 6 patients showed predominantly T-helper lymphocytes within the granuloma. NXG is a T-helper cell, non-X histiocytic granuloma with a distinctive histopathology.