Tropical pulmonary eosinophilia is a pulmonary condition caused by an overreactive immune response to microfilaria trapped in the lungs. Tropical pulmonary eosinophilia is a distinct entity with specific symptoms and diagnostic criteria that differentiate it from other types of eosinophilia in tropical regions.
This article discusses tropical pulmonary eosinophilia, a general view of the theme is available in the main article, eosinophilic lung disease.
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Epidemiology
Tropical pulmonary eosinophilia is a disease predominantly limited to tropical regions, with a distribution that overlaps Bancroft's filariasis 1-6. The condition is endemic in large areas of Africa, southern Asia, the Indian subcontinent, the Pacific Islands, and South America 1-6. Sporadic cases may occur in non-endemic countries due to travel or immigration 1-6.
Tropical pulmonary eosinophilia is more common in males than females, particularly in ages 15 to 40 years 1-6.
Diagnosis
Accurate diagnosis is crucial for the effective management and treatment of tropical pulmonary eosinophilia. Several factors support the filarial etiology of this disease, including 1-6:
residence in an endemic area for filariasis
nocturnal cough and dyspnea
demonstration of microfilariae fragments in lung biopsy material
strongly positive complement fixation test for filaria
elevated titers of anti-filarial antibodies
high serum levels of IgE and filarial-specific IgE and IgG
peripheral blood eosinophilia with levels greater than 3000 cells/mm3 or 20%
bilateral lung involvement on chest x-ray or CT
good therapeutic response to diethylcarbamazine
Clinical presentation
The clinical presentation of Tropical pulmonary eosinophilia is characterized by the association of hypereosinophilia with bronchitic-asthmatic symptoms, and misdiagnosis as asthma is frequent 1-6.
Patients with tropical pulmonary eosinophilia usually present with the following symptoms 1-6:
dyspnea, which can be severe and prolonged
chronic, paroxysmal cough, more frequent and intense at night
wheeze
chest pain due to rib fractures caused by vigorous coughing
low fever
weight loss
fatigue
malaise
Pathology
Tropical pulmonary eosinophilia occurs from a hypersensitivity response to microfilariae antigens, primarily those of Wuchereria bancrofti and Brugia malayi, present in the pulmonary microcirculation, which causes subsequent inflammation with eosinophils playing an essential role 1-6.
Microscopic appearance
The pathology of tropical pulmonary eosinophilia can range from acute eosinophilic alveolitis to histiocytic infiltration and may vary depending on disease severity 1,2,4,6.
Radiographic features
Plain radiograph
The chest radiograph usually shows bilateral and symmetrical pulmonary involvement 1-4. Radiographic findings typically improve with diethylcarbamazine treatment, but residual changes may persist in some patients 1-6. The commonly observed radiological pattern includes 1-6:
normal chest radiograph
bilateral diffuse reticulonodular opacities
bilateral miliary nodules
global reduction in lung transparency, better demonstrated when compared to normal radiographs obtained after treatment
rib fractures, with lower ribs being more commonly affected
CT
The CT is more sensitive and can demonstrate in more detail the radiological abnormalities 1,3-5:
interstitial pulmonary fibrosis in untreated cases
Treatment and prognosis
To effectively manage tropical pulmonary eosinophilia and prevent long-term respiratory complications, a timely and accurate diagnosis followed by treatment is crucial 1-6. Diethylcarbamazine is used to treat filariasis, including tropical pulmonary eosinophilia 1-6. Without treatment, patients may develop interstitial lung disease 1-6.
History and etymology
Tropical pulmonary eosinophilia was first reported in India in 1940 by Frimodt-Moller and Barton, who described the association of hypereosinophilia, bronchitic-asthmatic-like symptoms, and pulmonary infiltrates on chest x-rays 2,4,5. In 1943, Weingarten named the disease and described its clinical and radiological features 2,4,5.
Differential diagnosis
bronchial asthma
acute and chronic eosinophilic pneumonia
Loeffler syndrome secondary to drug reactions or parasitic helminth infections (ascariasis, ankylostomiasis, strongyloidiasis, schistosomiasis, toxocariasis, paragonimiasis)