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The Third Stage of Recovery. The third stage of recovery is characterized by the death of the parasite, after which a fibrotic reaction ensues and the cyst disappears (Fig. 22.35). Once diagnosed, paragonimiasis can be effectively treated with oral praziquantel, with a cure rate of 70% with one day therapy, and 90 to 100% with 2 and 3-day therapies (Shim et al 1991)(Fig. 22.22). The drug's mechanism of action is not completely elucidated.

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Fig. 22.35A-C. Paragonimiasis in a Korean man showing slight progressive healing of the small cystic lesions at the right lung base on serial chest films taken over a 1 year period. (A) PA chest film and (B) coned view of the right lower lung show a few small cysts with surrounding exudative reaction and tortuous worm burrows in the adjacent parenchyma. There are also small 1-cm ring-like shadows in the right upper lobe and suprahilar area (arrows). (C) A view of the right lower lung from a chest radiograph taken 11 months later shows the chronicity of the Paragonimus lesions, with slight change in the interval. Some of the surrounding exudative reaction has disappeared and has gradually been replaced by fibrosis. Note the horizontal linear strands extending to the overlying pleura along the lower lateral chest wall. Paragonimus cysts are commonly found in a peripheral or subpleural location and often show an overlying localized pleural reaction or linear stranding to the pleura as seen here. This patient was a 38-year-old North Korean with jaundice, generalized weakness, and right chest and hypochondrial pain that increased on deep breathing. He had a productive cough and his sputum contained P. westermani eggs, but no blood.

However, it increases the permeability of the integument to the calcium ion, immediately triggers the extreme contraction of the worm, and results in paralysis of the worm followed by lysis. The clinical symptoms and signs of the disease may totally disappear and the chest radiograph may eventually show either no residual lesions or irregular fibrotic linear opacities radiating into the surrounding pulmonary parenchyma. The time required for radiological resolution depends on the chronicity of the lesions; chronic lesions last longer and leave more fibrotic lesions after successful treatment. Fibronodular opacities may eventually resorb and calcify. These calcifications range from 2 to 5 mm in diameter and may closely resemble those of healed tuberculomas on plain radiographs and CT scans (Figs. 22.36, 22.37). However, unlike in cerebral paragonimiasis and pulmonary tuberculosis, calcification is uncommon in pulmonary paragonimiasis (Im et al, 1992). Because tuberculosis is widespread in the endemic areas where paragonimiasis is found, small pulmonary calcifications may represent healed lesions of either, or both, diseases.

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Fig. 22.36 A, B. The stage of recovery in pulmonary paragonimiasis is characterized by fibrosis and small calcifications ranging from 2 to 5 mm in size, as illustrated in these coned views of the midlung fields of two Korean men. P. westermani eggs were found in the sputa of both patients. In patient (A), there is a large aggregate of small ring shadows and cysts in the right midlung, each cyst measuring 1 cm or less. The cyst walls are well defined and thin. A corona effect produced by a crescent-shaped density in the lateral wall of the most lateral cyst (arrow) identifies the characteristic ring shadow of paragonimiasis. As these second stage lesions heal, the chest radiograph may show small homogeneous densities with fibrous cords radiating into adjacent pulmonary parenchyma. These densities may resorb with deposition of calcium, as seen in this patient, who has two small calcifications lateral to the hilus. (B) Another patient with small cystic lesions in the lateral aspect of the midlung as well as multiple 5 mm calcifications in the upper lobe and hilar region. Such calcifications are also seen in healed tuberculosis, and indeed the two diseases may coexist in the same individual since they are endemic in the same countries, especially in the Orient.

Fig. 22.37. Chronic pulmonary paragonimiasis in a 61-year-old Korean man presenting with calcified nodules in the lung. High-resolution CT shows 4 to 5-mm aggregated nodules in the right upper lobe containing calcifications. Calcification in pulmonary paragonimiasis is uncommon, but can occur in cases of chronic untreated lesions, as in this patient. P.
westermani
ova were found in needle aspirates of the right lung lesion. The patient was successfully treated with oral praziquantel; however, the calcified small nodules remained unchanged.

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