A hidden clue behind angioedema in an elderly patient.

Acquired angioedema (AAE) is a rare, potentially life-threatening condition caused by bradykinin, typically presenting as recurrent, non-pitting facial swelling without urticaria. Unlike hereditary forms, acquired angioedema arises later in life and may be associated with underlying B-cell lymphoproliferative disorders. We report a 62-year-old woman with persistent antihistamine-unresponsive facial angioedema, fatigue, and moderate splenomegaly, which led to further work-up for AAE. Low C4 and C1 inhibitor (C1-INH) was detected, with normal C1q levels. Given the presence of splenomegaly and cytopenia, further evaluation of lymphoproliferative disease was pursued. Bone marrow biopsy confirmed splenic marginal zone lymphoma (SMZL), and rituximab-based chemotherapy resulted in full remission of both lymphoma and angioedema. This case highlights the importance of evaluating elderly patients with unexplained angioedema and organomegaly for hidden lymphoproliferative disease. Treating the underlying disease can resolve symptoms and improve outcomes.