Pulmonary lymphoma of mucosa-associated lymphoid tissue type followed as a long-standing indeterminate lesion in immunoglobulin M-type paraproteinemia.

An 82-year-old woman with monoclonal immunoglobulin (Ig) M-type paraproteinemia had a large opacity in the right lung field. The abnormal shadow on roentgenogram had persisted for more than 6 years since the initial diagnosis of paraproteinemia, which had been diagnosed as Waldenström's macroglobulinemia (WM). Computed tomography revealed the lesion as a pulmonary tumor which was finally diagnosed as a marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) after surgical removal. MALT lymphoma constitutes the majority of primary pulmonary lymphomas and is often associated with monoclonal IgM-type paraproteinemia as well as WM, a distinctive lymphoproliferative disorder. Pulmonary MALT lymphoma should frequently be suspected in case of an indeterminate pulmonary tumor with IgM-type paraproteinemia.