MALT lymphoma mimicking IgG4-related disease.

A 75-year-old man presented with left eye fullness, proptosis, and bilateral lacrimal gland enlargement with elevated serum IgG4 levels, initially suggesting IgG4-related disease. However, lacrimal gland biopsy revealed MALT lymphoma. This case highlights the overlapping clinical features of IgG4-related disease and lymphoma and emphasizes the importance of histopathological confirmation before initiating treatment.