Atypical IgG4+ Plasmacytic Proliferations and Lymphomas: Characterization of 11 Cases

To report the clinicopathologic features of monotypic immunoglobulin G4+ (IgG4+) lymphoid and plasmacytic proliferations.

Cases were identified from the pathology files. Pathology and clinical materials were reviewed.

Eleven cases of monotypic IgG4+ proliferations were identified at nodal, orbital, or salivary sites. Six cases (three men, three women; age, 57-94 years) met criteria for lymphoma or plasma cell neoplasia. Most contained frequent Mott cells. Five cases (three men, two women; age, 40-80 years) had restricted proliferations of atypical/monotypic IgG4+ plasma cells in a background of reactive lymphoid hyperplasia or inflammation.

Monotypic IgG4+ proliferations include lymphomas, plasmacytic neoplasms, and a previously uncharacterized group of proliferations not meeting criteria for conventional hematolymphoid neoplasia. Distinct features included prominent Mott cells and/or monotypic plasma cells within follicles. The proliferations were infrequently associated with IgG4-related disease (IgG4-RD). Our findings raise questions regarding the relationship between clonal IgG4+ proliferations, reactive/inflammatory processes, and IgG4-RD.