Question
Tropical pulmonary eosinophilia.
Answer
Tropical Pulmonary Eosinophilia (TPE): an immunologically hyper-reactive (occult filarial) syndrome, occurring in a small proportion of individuals infected with lymphatic filarial parasites — Wuchereria bancrofti or Brugia malayi — representing an exaggerated host immune response to microfilariae, rather than a direct effect of the adult worms or overt lymphatic filarial disease.
Pathogenesis: microfilariae are rapidly cleared from peripheral blood by a hyper-immune (allergic-type) response, trapped and destroyed predominantly within the pulmonary vasculature, triggering marked local eosinophilic inflammation.
Clinical features: paroxysmal nocturnal cough, wheezing/asthma-like symptoms, dyspnoea, low-grade fever, and weight loss, typically in a young adult from an endemic (filarial) region.
Laboratory findings:
- Marked peripheral blood eosinophilia (often >3000 cells/μL, sometimes much higher).
- Elevated total serum IgE.
- High titres of anti-filarial antibody.
- Microfilariae characteristically ABSENT from peripheral blood (a key diagnostic feature, since they are sequestered/destroyed in the lungs rather than circulating) — distinguishing TPE from straightforward microfilaraemic filarial infection.
- Chest X-ray: diffuse miliary mottling or reticulonodular infiltrates.
- Dramatic clinical and eosinophil-count response to Diethylcarbamazine (DEC) therapy is both therapeutic and supportive of the diagnosis.
Treatment: Diethylcarbamazine (DEC), the drug of choice, typically producing marked clinical improvement.