Primary IgG4-related lymphadenopathy with prominent granulomatous inflammation and reactivation of Epstein–Barr virus

We report a unique case of primary IgG4-related lymphadenopathy showing prominent granulomatous inflammation and Epstein–Barr virus (EBV) reactivation. Involved lymph nodes showed an expanded interfollicular zone with prominent granulomatous inflammation, including a predominance of epithelioid macrophages and occasional Langhans multinucleated giant cells. Bundles of spindle cells were also observed. Intermingled with the granulomatous inflammation were numerous mature plasma cells, eosinophils, and neutrophils. The percentage of IgG4+/IgG+ plasma cells was markedly elevated (70%), along with raised serum IgG4 levels. The plasma cells did not show immunoglobulin light-chain restriction. EBV-positive lymphocytes were scattered throughout the paracortical areas. Corticosteroid treatment was very effective. IgG4-related lymphadenopathy has a broad histological spectrum and might be misdiagnosed due to other conditions which morphologically closely resemble it. The correct diagnosis is important in view of the remarkable response to steroid therapy.