IgM Pleural Amyloidosis Diagnosed by Pleural Effusion Cell Block: A Case Report

Immunoglobulin light chain (AL) amyloidosis is characterized by the systemic deposition of light-chain-derived amyloids. Immunoglobulin M (IgM)-associated AL amyloidosis is extremely rare and clinically distinct. A 70-year-old man presented with dyspnea, bilateral pleural effusion, and mediastinal lymphadenopathy on computed tomography (CT). Amyloid was detected in a pleural effusion cell block and confirmed via an axillary lymph node biopsy. Serum studies and bone marrow findings supported IgM-λ AL amyloidosis associated with Waldenström macroglobulinemia/lymphoplasmacytic lymphoma. First-line therapy failed, but second-line therapy reduced pleural effusion, avoiding thoracentesis for one year. A pleural effusion cell block analysis enabled rapid diagnosis with minimally invasive exploration.