A patient presents with fever, nocturnal cough, breathlessness, and wheezing for 4 weeks. Absolute eosinophil count >5000/µL. chest x- ray shows a miliary pattern. What is the likely diagnosis?

Explanation

## Correct Answer: C. Tropical pulmonary eosinophilia Tropical pulmonary eosinophilia (TPE) is a hypersensitivity reaction to filarial antigens, endemic in India, Southeast Asia, and the Pacific. The clinical triad of **nocturnal cough, breathlessness, and wheezing** lasting weeks to months, combined with **absolute eosinophil count >5000/µL** and **miliary pattern on CXR**, is pathognomonic for TPE. The nocturnal cough is a hallmark feature—patients often report severe coughing fits at night due to microfilaremia peaking in peripheral blood during sleep. The miliary pattern reflects diffuse granulomatous inflammation from immune complex deposition in alveoli and interstitium. Unlike asthma (which lacks eosinophilia and miliary infiltrates) or miliary TB (which shows normal or low eosinophils), TPE presents with marked peripheral eosinophilia (often >5000/µL, sometimes >10,000/µL). Diagnosis is confirmed by elevated IgE levels, positive filarial serology (IHA/ELISA), and response to diethylcarbamazine (DEC) therapy. In India, TPE remains a common cause of chronic respiratory symptoms in endemic areas, particularly in coastal and tropical regions. ## Why the other options are wrong **A. Miliary tuberculosis** — Miliary TB does present with fever, cough, and miliary CXR pattern, but it does NOT cause marked peripheral eosinophilia (eosinophil count typically normal or low). TB-induced eosinophilia is rare and mild. The combination of miliary pattern + high eosinophil count >5000/µL strongly excludes TB. Additionally, miliary TB is acute/subacute (days to weeks), whereas TPE is more indolent (weeks to months). **B. Bronchial asthma** — Asthma presents with wheezing and breathlessness but does NOT produce miliary infiltrates on CXR or marked peripheral eosinophilia (eosinophils may be mildly elevated in eosinophilic asthma, but rarely >5000/µL). The miliary pattern is a key discriminator—asthma causes bronchial wall thickening and hyperinflation, not diffuse granulomatous infiltrates. Nocturnal cough in asthma is due to airway hyperresponsiveness, not filarial antigen-driven inflammation. **D. Hypersensitivity pneumonitis** — Hypersensitivity pneumonitis (HP) can present with cough, breathlessness, and miliary/nodular infiltrates, but it requires a clear history of antigen exposure (organic dusts, bird proteins, etc.). HP does NOT typically cause marked peripheral eosinophilia >5000/µL; lymphocytosis is more common. The nocturnal cough pattern and high eosinophil count are not features of HP. In India, TPE is far more common than HP in this clinical context. ## High-Yield Facts - **Nocturnal cough** is the hallmark symptom of TPE—microfilariae peak in peripheral blood during sleep, triggering immune-mediated inflammation. - **Absolute eosinophil count >5000/µL** (often >10,000/µL) is a cardinal feature; other causes of miliary pattern (TB, HP, asthma) do not produce this degree of eosinophilia. - **Miliary pattern on CXR** reflects diffuse alveolar and interstitial granulomatous inflammation from filarial antigen–antibody complexes. - **Elevated serum IgE** (often >1000 IU/mL) and **positive filarial serology** (IHA, ELISA) confirm diagnosis; microfilariae are rarely found in sputum or blood. - **Diethylcarbamazine (DEC) 6 mg/kg/day for 12 days** is the DOC in India; response within 2–4 weeks (symptom resolution, eosinophil normalization) confirms diagnosis. - **Endemic in coastal and tropical India** (Kerala, Tamil Nadu, Andhra Pradesh, Odisha); Wuchereria bancrofti is the causative agent in most Indian cases. ## Mnemonics **TPE Triad** **N**octurnal cough + **E**osinophilia (>5000) + **M**iliary pattern = TPE. Use when you see nocturnal cough + high eosinophils—think filarial disease first in endemic areas. **DEC Response Test** If diagnosis is uncertain, empirical DEC 6 mg/kg for 12 days with symptom/eosinophil resolution = TPE confirmed. This is a practical bedside diagnostic tool in India. ## NBE Trap NBE may pair miliary pattern with TB to lure students into reflexive TB diagnosis, overlooking the critical discriminator: marked peripheral eosinophilia (>5000/µL) is incompatible with TB and points to TPE. The nocturnal cough pattern is also a red herring if students conflate it with TB cough. ## Clinical Pearl In an Indian patient from endemic coastal regions presenting with chronic nocturnal cough and high eosinophils, always ask about filarial exposure and consider TPE before pursuing TB workup. A therapeutic trial of DEC often clinches the diagnosis faster than serology in resource-limited settings. _Reference: Harrison Ch. 397 (Filarial Infections); Robbins Ch. 8 (Infectious Diseases); KD Tripathi Ch. 48 (Anthelmintics)_