Tropical pulmonary eosinophilia is a rare but well recognised syndrome which results from immunologic hyper responsiveness to human filarial parasites, Wuchereria bancrofti and Brugia malayi, is characterized by cough, dyspnea and nocturnal wheezing, diffuse reticulonodular infiltrates in chest radiographs, and marked peripheral blood eosinophilia
This condition is more widely recognised and promptly diagnosed in filariasis-endemic regions, such as the Indian subcontinent, Africa, Asia and South America. In non-endemic countries, patients are commonly thought to have bronchial asthma.The most common misdiagnosis is asthma, with overlapping symptoms of chronic cough, paroxysmal dyspnoea and wheeze.
Early recognition and treatment with the antifilarial drug, diethylcarbamazine, is important, as delay before treatment may lead to progressive interstitial fibrosis and irreversible impairment.
The condition of marked eosinophilia with pulmonary involvement was first termed tropical pulmonary eosinophilia
However, only a small percentage (< 0.5%)of the 130 million people globally who are infected with filariasis apparently develop this reaction.
The clearance of rapidly opsonised microfilariae from the bloodstream results in a hypersensitive immunological process and abnormal recruitment of eosinophils, as reflected by extremely high IgE levels of over 1000 kU/L. The typical patient is a young adult man from the Indian subcontinent
The diagnostic criteria for tropical pulmonary eosinophilia include:
- history supportive of exposure to lymphatic filariasis;
- peripheral blood eosinophils more than 3000 cells/mm3
- a history of paroxysmal nocturnal cough and breathlessness,
- chest radiographic evidence of pulmonary infiltrations,
- leucocytosis in blood,
- elevated serum IgE levels (> 1000 kU/L);
- increased titres of antifilarial antibodies;
- peripheral blood negative for microfilariae;
- and clinical response to diethylcarbamazine.
The antifilarial diethylcarbamazine (6 mg/kg/day for 21 days) remains the main therapeutic agent and is generally well tolerated.