Laboratory Studies
- A CBC count with differential usually reveals eosinophilia in 10-30% of patients with paragonimiasis. The degree of eosinophilia is significantly higher in patients who have pleurisy. Leukocytosis with eosinophilia occurs early in the course of disease but then resolves over time.[2] Despite remarkable eosinophilia, total WBC count remains in the normal range or slightly elevated.
- Obtain clinical samples for ova and parasites.
- Definitive diagnosis of paragonimiasis requires detection of eggs in sputum, feces, pleural fluid, cerebrospinal fluid (CSF), or pus.[8, 9] However, eggs may not be present in feces and sputum for 2-3 months.[1]
- Worms or eggs may be found in biopsies of pulmonary, cerebral, subcutaneous, or intra-abdominal nodules or cystic lesions. The specific species causing paragonimiasis can be identified from adult or immature flukes found in surgical specimens (rarely in the sputum).
- Egg detection rates for paragonimiasis average 25-35% for a single sputum specimen but may reach 50% with multiple examinations. (As many as 7 examinations have been recommended.) The yield for specimens obtained via bronchoscopy is 53-67%.
- Stool examinations are very useful to diagnose paragonimiasis in children because children tend to swallow sputum.
Imaging Studies
- Chest radiography reveals abnormalities in approximately 80-90% of patients; however, chest films are normal in 13-20% of confirmed cases.[2] Radiographic abnormalities may include ring shadows, which represent cavitating lesions, fibrosis, nodules or linear infiltrates with calcified foci, loculated pleural effusions, and pleural thickening.
- Three radiographic stages of pulmonary infection have been described.[8]
- Migration of larvae can result in pneumothorax with consolidation or exudative pleural effusions.
- During fluke maturation nodular or cystic lesions predominantly develop in the periphery of the middle and lower lobes. Bronchiectasis can also occur.
- Following treatment lesions gradually disappear over 3-26 months.
- CT scanning or MRI of the head may reveal cerebral calcification, cystic lesions, or hydrocephalus. Chronic cerebral paragonimiasis may be suspected by the presence of a "soap bubble lesion," with scattered calcifications.
Other Tests
- Serology for paragonimiasis is useful because of the relatively low percentage of egg detection. Serologic tests aid in diagnosing extrapulmonary disease where eggs are not shed in the sputum or stool.
- The complement fixation test is sensitive and is most useful following therapy because antibody levels fall 6-12 months after effective treatment.
- The technical difficulties inherent in the complement fixation test make enzyme-linked immunosorbent assay (ELISA) the serological test of choice. ELISA has 92% sensitivity and is specific; however, antibody levels often take longer (ie, < 24 mo) to return to the reference range after successful treatment. Low-level positive results may occur with other trematode infections.
- A rapid immunoblot test developed by the Centers for Disease Control and Prevention is 96% sensitive and 99% specific but cannot be used to differentiate active from past infection.
- Skin testing
- Intradermal skin testing with an extract of adult Paragonimus is reasonably sensitive, although rare false-negative results could occur. Results may remain positive for as long as 20 years after cure.
- Skin testing is useful as an epidemiologic tool to detect prevalence of infection and is the most commonly used test for screening. Because this test can cross react with Clonorchis sinensis and Schistosoma japonicum, it should only be used for purposes of screening.[1]
Procedures
- Lumbar puncture: Examination of infected CSF reveals bloody or turbid fluid containing numerous eosinophils.
- Thoracentesis: Infected pleural fluid is usually serosanguineous and has more than 1000 red cells with accompanying eosinophilia. The fluid is usually an exudate with a low glucose level. Parasitic eggs are rarely detected in the sediment of pleural effusions.
- Biopsy: Lung biopsy specimens usually reveal adult worms or eggs.
Histologic Findings
- Pathological findings in the lung vary and depend on the worm burden and disease chronicity.
- Adult flukes are typically encapsulated in cysts, which tend to occur in the right lung. Patients usually have fewer than 20 cysts, each of which contains 2-4 flukes. The cyst wall is thick, sclerotic, and sometimes calcified.
- Microscopically, the cyst wall contains granulation tissue with fibroblasts, mononuclear cells, plasma cells, lymphoid cells, and eosinophils.
- Numerous Charcot-Leyden crystals and eggs are formed in the cavity, and egg-containing granuloma frequently develop near the cyst.
- Bronchial arteries may show hypertrophy or may rupture from damage.
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