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Tropical Pulmonary Eosinophilia

Tropical pulmonary eosinophilia (TPE) was first described in 1939 in a group of seven Javanese men. Over the next few years, other cases were reported, with lymph node biopsies showing eosinophilic granulomata surrounding microfilariae. The term "pseudo-tuberculous condition" was used to describe these patients with dyspnea (often severe), eosinophilia, and extensive mottling of the lungs on chest radiographs. Adult filariae were never recovered, nor was there evidence of lymphatic obstruction. Splenomegaly and fever were also described and, in contrast to Löffler's syndrome, this illness persisted for months and was responsive to treatment with certain anthelmintic drugs or arsenicals.

Synonyms

Occult filariasis. Weingartner's syndrome. Meyer's-Kouwenaar syndrome. Pseudo-tuberculosis of the lung. Eosinophilic pseudo-leukemia. Tropical eosinophilic asthma. Frimödt-Möller and Barton syndrome.

Definition

Tropical eosinophilia is an immune hyperresponse to filarial infection. The syndrome includes a high eosinophil count, pulmonary symptoms and radiological changes, fever, dyspnea, and loss of weight.

Geographic Distribution

Tropical pulmonary eosinophilia is reported from southern India, Sri Lanka, Malaysia, and Southeast Asia, but also occurs in the Caribbean, South America, Africa, and Polynesia. It is most common in India and Southeast Asia.

Epidemiology and Pathology

There are some findings in the epidemiology of TPE which have not been explained. These include predominance of disease in males (4:1 male: female predominance) and an age group of 20-40 years. The geographic distribution suggests that Brugia spp. are a causative filarial parasite; however, W. bancrofti has been implicated and the etiology is still not completely clear. Indeed, Toxocara canis, Ankylostoma, and Strongyloides have also produced similar clinical syndromes.

The etiology was unknown for two decades, but (as indicated above) it is now agreed that it is an immune hyperresponse to microfilariae. Patients present with breathlessness, which can be severe, and a paroxysmal cough, which is often nocturnal but is accompanied by little sputum production. There is often weight loss, wheezing, and a low-grade fever with occasional hemoptysis. Extrapulmonary manifestations occur in about 15% of patients and include splenomegaly, hepatomegaly, and lymphadenopathy. Blood samples show a hypereosinophilia of 3000 to 50,000 cells/mm³, but no microfilariae. The other characteristic features are a high IgE level, seropositivity to filarial antibody, and rapid clinical improvement with administration of diethylcarbamazine.

Lung biopsy specimens show an eosinophilic bronchitis and bronchopneumonia, with multiple small granulomata and areas of necrosis (microabscesses). Foreign body giant cells are common, forming tubercle-like nodules. While intact microfilariae are not generally seen, there may be fragments in the granulomata. The eosinophilic debris, in the form of Splendore-Hoeppli material, implicates helminthic infection. If other organs are biopsied, microfilariae may then be identified (Fig.26.35). Liver biopsy shows eosinophilic infiltration along the portal tracts and sinusoids, with associated focal necrosis. Many patients show impaired lung function with reduction of vital capacity, total lung function, and residual volume. A constant and characteristic feature of TPE is peripheral blood hypereosinophilia (3,000-50,000 cells/mm³) in the presence of circulating filarial antibodies. The term "occult filariasis" has been applied to this condition, as these patients do not demonstrate a microfilaremia on blood smear. A filarial origin can be diagnosed histopathologically when lymph node and other biopsies show trapped microfilariae. A rapid response to diethylcarbamazine or positive serology will be diagnostic. If TPE goes untreated, there may be progression to chronic pulmonary fibrosis.

Fig. 26.35. The histopathology of tropical pulmonary eosinophilia. A section from a lung biopsy showing a pulmonary granuloma. Microfilariae are not identified, but there is an intense eosinophilic inflammatory reaction.

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Copyright: Palmer and Reeder