Concurrent IgG4-Related Disease and Primary Chest Wall MALT Lymphoma on 18F-FDG PET/CT

A 62-year-old man presented with chronic eyelid swelling and bilateral visual disturbance. Markedly elevated serum IgG4 levels and a favorable response to glucocorticoid therapy, and IgG4-related disease (IgG4-RD) were clinically considered. ¹⁸ F-FDG positron emission tomography/computed tomography (PET/CT) for systemic assessment demonstrated typical multisystem IgG4-RD involvement, with an isolated right chest wall nodule showing focal, site-atypical FDG uptake. Biopsy confirmed the diagnosis of primary mucosa-associated lymphoid tissue (MALT) lymphoma with plasmacytic differentiation. We report a rare case of the concurrent IgG4-RD with primary chest wall MALT lymphoma and suggest MALT lymphoma should be considered in the differential for discordant focal lesions on PET/CT in known IgG4-RD.