Human pulmonary dirofilariasis in a patient whose clinical condition altered during follow-up.

Pulmonary dirofilariasis is a rare disease. We have experienced a case which developed pleural effusion while being followed, rendering it difficult to establish the diagnosis. The patient, a 53-year-old woman, had previously undergone two operations; one for uterine cancer and another for breast cancer. She developed a cough in February 2002, and chest computed tomography (CT) scans disclosed a nodular mass in the right lung. A biopsy revealed a fibrous nodule with macrophage aggregation. Pleural effusion was demonstrated on chest CT scans performed in May. As the possibility of malignant tumor could not be ruled out, an operation was undertaken. The nodular lesion showed marked coagulation necrosis, and dead parasites were noted in the vascular lumen. The parasites had the characteristic morphological features of Dirofilaria immitis. Immunological studies produced a positive test result for the anti-dirofilaria immitis antibody; hence a diagnosis of pulmonary dirofilariasis was made.