Necrobiotic Xanthogranuloma With Associated Monoclonal Gammopathy Presenting as an Eyelid Nodule.

Necrobiotic xanthogranuloma (NXG) is a progressive non-Langerhans cell histiocytosis with a predilection for the periorbital area. NXG is most commonly associated with monoclonal gammopathy and ophthalmic complications. The authors present a 69-year-old man who was evaluated for a left upper eyelid nodule and plaques on the lower extremities, trunk, abdomen, and right upper extremity. Biopsy of the eyelid was supportive for NXG. Serum protein electrophoresis was positive for a monoclonal gammopathy, IgG light chain kappa. MRI showed preseptal involvement. The periocular nodules cleared with a high dose of prednisone; however, the other skin lesions persisted. Bone marrow biopsy showed kappa-restricted 6% plasma cells and he was treated with intravenous immunoglobulin. This case illustrates the importance of clinicopathologic correlations to render an NXG diagnosis.