Immunoglobulin G4–Related Lymphadenopathy

Immunoglobulin G4–related lymphadenopathy (IgG4-RLAD) occurs in the setting of extranodal IgG4-related disease (IgG4-RD), an immune-mediated process described in many organ systems characterized by lymphoplasmacytic infiltrates with abundant IgG4-positive plasma cells and fibrosis. Although the morphologic features in the lymph node sometimes resemble those seen at the extranodal sites, 5 microscopic patterns have been described, most of which resemble reactive lymphoid hyperplasia. This morphologic variability leads to unique diagnostic challenges and a broad differential diagnosis. As IgG4-RD may be exquisitely responsive to steroids or other immunotherapy, histologic recognition and inclusion of IgG4-RLAD in the differential diagnosis is vital.