Elevated serum IgG4 levels in two cases of paragonimiasis

Paragonimiasis is a parasitic pleuropulmonary infection caused by eating raw crustaceans and wild boar meat and this infection is endemic in Asia. We herein report two cases of pulmonary Paragonimus westermani infection associated with elevated levels of serum immunoglobulin (Ig) G4 and dense infiltration of IgG4-positive plasma cells in the lung lesions. Treatment with praziquantel resolved the pulmonary lesions and decreased the serum levels of IgG4. IgG4-related disease is a systemic disease occasionally involving the lungs and leads to increased serum levels of IgG4. Our findings suggest that P. westermani infection requires a differential diagnosis from IgG4-related diseases and the serum IgG4 level may be a potentially useful marker of P. westermani infection.