Pulmonary Dirofilaria immitis Infection and Concurrent Pleural Lymphangiomatosis in a Young Woman from Costa Rica: A Diagnostic Challenge after 20 Years of Silence.

Human dirofilariasis is an underreported, vector-borne disease caused by the filarioid Dirofilaria immitis. A case of pulmonary dirofilariasis is reported in a woman from Costa Rica, manifesting respiratory distress, marked eosinophilia of 47%, and severe chylothorax. Pleural biopsies revealed a lymphoplasmacytic reaction with eosinophils, and bronchoalveolar fluid analysis revealed 28S and internal transcribed spacer 1 fragments that were 100% and 99.3% similar to D. immitis, respectively, and a coxA sequence identical to Wolbachia from D. immitis. Other infectious, autoimmune, and malignant causes were excluded through an extensive diagnostic workup. Initial treatment included methylprednisolone, albendazole, and a subsequent course of albendazole plus doxycycline; however, the chylothorax recurred. A biopsy of the left upper lobe confirmed a pleural lymphangiomatosis. The patient was discharged with continued treatment but was clinically stable. This case reveals the diagnostic complexity of filariasis and underlying lymphadenopathies coexisting in endemic regions and highlights the value of an integrated clinical, molecular, and histopathological approach.