A 74-year-old man was referred to our hospital because of dyspnea on exertion and a large left-sided pleural effusion. The eosinophil count increased in the pleural effusion. Parasite-specific serum antibodies were examined, but no significant results were obtained. He was diagnosed with hypereosinophilic syndrome. Prednisolone was prescribed, and the pleural effusion symptoms improved. Prednisolone was accordingly tapered, then the treatment was terminated.
However, he was referred to our department again 2 years later because of the same symptoms. The parasite-specific serum antibodies were re-examined, and the Paragonimiasis westermani antibody titer had by then increased. We discovered that he had eaten wild boar meat prior to the appearance of the symptoms. He was diagnosed with Paragonimiasis westermani infection, and he responded to praziquantel administration. If it is difficult to diagnose the cause of eosinophilic pleural effusion, careful history-taking and re-examination of the parasite infection should be considered.