Necrobiotic Xanthogranuloma (NXG): Dermoscopic and Reflectance Confocal Microscopic Findings and Review of Treatment with Intravenous Immunoglobulin (IVIG).

Necrobiotic xanthogranuloma (NXG) is a rare, chronic non-Langerhans cell histiocytosis strongly associated with paraproteinemia and hematologic disorders. This study aims to present a clinical case of NXG, with particular emphasis on the dermoscopic and reflectance confocal microscopic (RCM) findings, and to review the literature on the efficacy of intravenous immunoglobulin (IVIG) therapy in this condition. A 58-year-old woman presented with progressive yellow-orange plaques, showing irregular vessels and hemorrhagic dots on dermoscopy. RCM displayed multiple large refractive cells and smaller cells with horseshoe-like structures, corresponding to xanthomatous histiocytes and Touton cells, respectively. Diagnostic evaluation revealed monoclonal IgG gammopathy and an indolent B cell lymphoma. Long-term treatment with IVIG combined with systemic glucocorticosteroids resulted in partial improvement. A review of 16 cases with follow-up available indicates that IVIG is a highly effective therapeutic option for NXG, often leading to rapid and significant improvement or complete remission. However, long-term responses vary, and interruption of therapy may result in disease relapse, suggesting the importance of sustained treatment. In conclusion, NXG is a multisystem disease showing several characteristics in noninvasive imaging methods. Although IVIG appears highly effective, variability in treatment response highlights the need for individualized management and for further research to better understand disease pathogenesis.