Subcutaneous Migration in Paragonimiasis as a Diagnostic Clue in an Unusual Presentation: A Case Report

Paragonimiasis is a foodborne parasitic infection caused by trematodes of the genus <i>Paragonimus</i>, primarily <i>P. westermani</i> and <i>P. miyazakii</i> in Japan. Though once endemic, its incidence has declined significantly in recent decades. However, globalization, changes in dietary customs, and an increase in foreign-born residents have contributed to the emergence of new cases, particularly in urban settings. We present a case of a 25-year-old man from Cambodia, living in Japan for two years as a technical intern trainee, who developed a productive cough and pleuritic chest pain. He reported consuming raw Japanese mitten crabs seven months earlier. Initially misdiagnosed with pneumonia, his symptoms persisted despite antibiotic therapy. CT imaging revealed pleural effusion, a cavitary lesion, and a linear tract consistent with worm migration. A subcutaneous abdominal mass was noted and surgically removed. Histopathological examination revealed eosinophilic infiltration and serpiginous necrosis, suggesting larval migration. Laboratory tests showed marked eosinophilia (11,011/μL), and pleural fluid analysis indicated pseudochylothorax. ELISA confirmed antibodies against <i>P. westermani</i> and <i>P. miyazakii</i>. The patient was treated with praziquantel, leading to complete clinical and radiological resolution. This case highlights the diagnostic challenges of paragonimiasis, especially with atypical presentations. Subcutaneous lesions are rare and often mimic benign tumors or other parasitic diseases, such as sparganosis or cysticercosis. The pulmonary findings may be confused with tuberculosis or eosinophilic pneumonia. Thus, thorough dietary and travel history-taking, cultural awareness, and a multidisciplinary diagnostic approach, including imaging, histology, and serology, are essential. Diagnosis of paragonimiasis should rely on a combination of clinical presentation, radiological findings, and serological testing, as ectopic manifestations are uncommon and may not be promptly recognized. This case underscores the need for heightened clinical awareness of re-emerging parasitic diseases in increasingly multicultural societies.