A case of IgG4-related disease potentially triggered by COVID-19 vaccination: longitudinal serum IgG4 monitoring from prevaccination.

We report a case of a 64-year-old Japanese man who developed IgG4-related pericoronary arteritis following mRNA-based COVID-19 vaccination. The patient presented with anterior chest pain and imaging revealed perivascular soft tissue thickening around the coronary arteries, along with pancreatic enlargement, enlarged prostate, and periaortitis. Laboratory tests showed markedly elevated serum IgG4 levels (1740 mg/dl). Histopathological findings from prostate biopsy were consistent with IgG4-related disease. Notably, retrospective analysis of preserved serum samples demonstrated a sharp increase in IgG4 levels following the third BNT162b2 vaccine dose, suggesting a possible link between vaccination and disease onset. The patient responded to prednisolone, with significant clinical and radiological improvement. However, IgG4 levels rebounded during tapering, requiring additional immunosuppressive therapy with azathioprine and planned rituximab treatment. This case represents the first documented instance tracking longitudinal changes in serum IgG4 levels from prevaccination through disease onset. While a definitive causal relationship between COVID-19 vaccination and IgG4-related disease remains unproven, this case highlights the need for further investigation into the potential immunopathogenic mechanisms involved.