Pneumothoraces and free pleural effusions may require tube or catheter drainage. However, in most patients, these are completely cured with praziquantel only. If the patient is treated early, the chest radiograph returns entirely to normal. However, in cases of chronic pleural effusion or empyema, pleural thickening with blunting of the costophrenic sulcus remains. Chronic contraction of the empyema sac may result in a small loculated collection of milky calcium ("milk of calcium of the pleura").

An unusual presentation seen in occasional patients with paragonimiasis is a hypersensitivity reaction similar to Löffler's syndrome. The peripheral blood will contain 16 to 39% eosinophils. Chest radiographs show ill-defined, mottled, fleeting densities, usually in the periphery of the lungs. These fluffy densities may disappear in one area, only to appear in another area of the same or opposite lung. The actual mechanism is a hypersensitivity reaction to the presence of P. westermani, as is the case with other allergens or parasites in Löffler's syndrome. The excysted worms are irritating to the lung tissues, either in the course of their migration through the subpleural space into the lungs or during lodgement in the pulmonary parenchyma in the vicinity of bronchioles, where they develop to mature flukes. A hyperallergic reaction ensues with fleeting pulmonary infiltrates, characteristically peripheral in location, associated with eosinophilia (Figs. 22.38, 22.39). The typical cystic nodules or ring-like lesions of paragonimiasis eventually develop at the sites of the transient pneumonic infiltrates; at this time, the eggs of P. westermani may be recovered in the sputum.

Fig. 22.38. Löffler's pneumonia in a 45-year-old woman caused by paragonimiasis. High-resolution CT scan obtained at the level of the left upper lobe bronchus shows multiple patchy "cotton wool" areas of airspace consolidation in both lungs. The patient had a mild cough and showed peripheral eosinophilia. Paragonimus-specific antibody test by micro-ELISA was positive.

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Fig.22.39A,B. Löffler's syndrome in a 29-year-old Korean recently immigrated to the United States. There was a high blood eosinophill count in the blood and there were characteristic fleeting pulmonary densities within the periphery of the lungs over a 2 week period. (A) Admission chest film shows a large homogeneous density in the lateral aspect of the right lower lung. (B) A chest radiograph taken 2 weeks later shows a similar homogeneous density in the lateral aspect of the left midlung as well as a smaller fluffy density in the right upper lobe underlying the clavicle. The findings are characteristic of Löffler's syndrome with transient mottled densities which may disappear in one area only to reappear shortly thereafter in another portion of the same or opposite lung. Löffler's syndrome represents a hyperallergic pulmonary reaction of varying etiology, but worldwide the most common cause is the larval phase of various parasites, including P. westermani, as they pass through the lungs. The etiology of Löffler's syndrome in this patient was not established. This case is presented here because it illustrates the typical radiographic findings in this syndrome, which is seen frequently in the tropics and not infrequently in temperate climates as well. (See also Chapter 10-Ascariasis, and Chapter 26-Filarial Diseases).