Necrobiotic Xanthogranuloma on 18F-FDG PET/CT.

We report the case of a 57-year-old man who presented with a 6-year history of yellowish plaques on his left buttock and right medial knee, as well as ulcerating subcutaneous nodules on his forearms bilaterally. Skin biopsy, bone biopsy, and serum protein electrophoresis confirmed the diagnosis of necrobiotic xanthogranuloma with associated monoclonal gammopathy. Necrobiotic xanthogranuloma is a rare form of non-Langerhans histiocytosis characterized by development of chronic cutaneous nodules that enlarge over time to form plaques. The author discusses necrobiotic xanthogranuloma's presentation and the utility of F-FDG PET/CT in disease staging, localizing optimal biopsy sites, and assessing treatment response.