Quantitative total serum IgG4 reporting in human paragonimiasis: a scoping review.

BACKGROUND: Paragonimiasis is a food-borne parasitic disease caused by lung flukes belonging to the genus Paragonimus. It can produce pulmonary, pleural, and other organ manifestations that overlap clinically, radiologically, and histopathologically with malignancy, tuberculosis, and immune-mediated disorders. Elevated total serum immunoglobulin G4 (IgG4) concentrations and IgG4-positive plasma cell infiltration may mimic IgG4-related disease (IgG4-RD), but quantitative serum IgG4 levels in paragonimiasis have not been systematically characterized. METHODS: We conducted a multi-database scoping review of human paragonimiasis case reports and case series published from January 1, 1965, to December 31, 2025. PubMed, Ichushi-Web, Chinese National Knowledge Infrastructure (CNKI), and KoreaMed were searched using database-specific strategies, supplemented by multilingual Google Scholar checks. The review was reported in accordance with the PRISMA-ScR checklist. RESULTS: Among 610 reports comprising 886 cases, quantitative serum IgG4 values were reported in 10 reports (1.6%) and 12 cases (1.4%). The countries of first-author affiliation were Japan (n = 6), China (n = 2), Thailand (n = 1), and France (n = 1), and all reports were published in 2012 or later. The 12 cases included pulmonary, pleural/intrathoracic, pericardial, central nervous system, and adrenal presentations. Among the 11 cases reported in mass concentration units, serum IgG4 values ranged from 94.1 to 3,350 mg/dL, and 10 values were elevated. The remaining case was reported as elevated (1,990 IU/mL) but was not converted to mass concentration units. Tissue pathology was described in 8 cases, and IgG4-positive plasma cell infiltration, IgG4-positive inflammation, or an increased tissue IgG4/IgG ratio was reported in 4 cases. None of the pathology reports described storiform fibrosis or obliterative phlebitis, which are hallmarks of IgG4-RD. Based on the information available in the original publications, none of the 12 cases were mapped as probable or definite IgG4-RD. CONCLUSION: Quantitative serum IgG4 values are rarely reported in paragonimiasis case literature, and selective testing and reporting precluded estimation of the prevalence of serum IgG4 elevation. Serum IgG4 elevation and IgG4-positive plasma cells should be interpreted together with exposure history, parasite-directed evidence, and histopathology. Early consideration of paragonimiasis may prevent delayed diagnosis and inappropriate immunosuppression owing to misdiagnosis.