Necrobiotic xanthogranuloma presenting as a solitary tumor

We report on a 60-year-old overweight white woman who presented with an asymptomatic flat, hard, yellow-brown subcutaneous plaque on her right hip. A total excision was performed. Histopathologic examination showed all the major features of a necrobiotic xanthogranuloma (NX) involving the entire dermis and subcutis, including areas of necrobiosis with cholesterol clefts, granulomatous infiltrate with some bizarre giant cells, numerous Touton cells, foamy cells, lymphoid follicles with germinal centers, foci of plasma cells, and "Touton cell panniculitis." A laboratory investigation revealed only slightly increased titers of cholesterol, strong positivity of anti-Borrelia antibodies, and diffuse skeletal osteoporosis with fractures of seven vertebrae. After 4 years of close follow-up, the osteoporosis was improved, and there were no signs of paraproteinemia, malignancy, or new skin lesions. The authors suggest that this case could represent a solitary clinical variant of NX without paraproteinemia.