Necrobiotic xanthogranuloma: Highlighting the role of clinicopathologic correlation in an atypical presentation.

Necrobiotic xanthogranuloma (NXG) is a rare, chronic non-Langerhans cell histiocytosis that clinically manifests as yellow to orange papules or nodules, most commonly involving the periorbital region. Histopathologic features include necrobiotic collagen, multinucleated giant cells (including Touton and Langhans types), granulomatous inflammation with xanthomatous histiocytes, extracellular lipid, and occasionally lymphoid follicles and plasma cells. NXG has a well-documented association with monoclonal gammopathies and extracutaneous malignancies, although the underlying pathogenic mechanisms remain poorly understood. We report the case of a 72-year-old woman presenting with erythematous plaques on the abdomen and extremities. Despite the absence of classic facial involvement and an initial nondiagnostic skin biopsy, further evaluation revealed a clonal plasma cell disorder classified as borderline between monoclonal gammopathy of undetermined significance and smoldering multiple myeloma. A subsequent biopsy demonstrated diagnostic features of NXG. This case underscores the importance of integrating clinical findings with histopathologic evaluation to achieve an accurate diagnosis.