A 26-year-old man from coastal Kerala presents with 5 weeks of severe paroxysmal nocturnal cough, wheeze, and low-grade fever. Peripheral blood shows an absolute eosinophil count of 4,800/μL and markedly elevated anti-filarial IgG and IgE titers. Chest radiograph shows fine reticulonodular opacities with mid and lower zone predominance. Spirometry is performed. The structure marked **A** (FEV1/FVC 0.62) indicates which of the following as the dominant spirometric abnormality in this patient?
A. Restrictive pattern from interstitial eosinophilic infiltration alone
B. Emphysematous destruction of elastic recoil
C. Pure diffusion impairment without airway involvement
D. Airflow obstruction due to bronchospasm and eosinophilic airway infiltration in tropical pulmonary eosinophilia
Explanation
Why "Airflow obstruction due to bronchospasm and eosinophilic airway infiltration in tropical pulmonary eosinophilia" is right
The FEV1/FVC ratio of 0.62 (marked as A) is pathognomonic for airflow obstruction, defined as FEV1/FVC <0.70. In tropical pulmonary eosinophilia (TPE), the dominant spirometric phenotype is a mixed obstructive-restrictive defect, but the obstructive component—reflected in the reduced FEV1/FVC ratio—is the primary abnormality that drives the bronchospastic symptoms (paroxysmal nocturnal cough and wheeze) and is the target of diethylcarbamazine (DEC) therapy. The obstruction results from both acute bronchospasm triggered by the Th2 hypersensitivity response to occult filarial infection and eosinophilic infiltration of the airway wall. This is the defining spirometric feature of TPE in this patient (Vijayan VK. Tropical pulmonary eosinophilia. Curr Opin Pulm Med. 2022).
Why each distractor is wrong
Restrictive pattern from interstitial eosinophilic infiltration alone: While TPE does have a restrictive component (TLC 80% predicted, DLCO 70% predicted), the FEV1/FVC ratio of 0.62 specifically indicates obstruction, not restriction. A restrictive pattern would show a normal or elevated FEV1/FVC ratio (>0.70) with reduced FVC and TLC.
Pure diffusion impairment without airway involvement: The DLCO is mildly reduced at 70% predicted, but this is not the dominant abnormality. The FEV1/FVC ratio directly reflects airway obstruction, not diffusion impairment alone. Diffusion impairment would not explain the reduced peak expiratory flow and concave flow-volume loop.
Emphysematous destruction of elastic recoil: TPE is not associated with emphysema or destruction of elastic tissue. The obstruction is functional and reversible (14% improvement post-bronchodilator), not structural. Emphysema would show a fixed obstructive pattern unresponsive to bronchodilators.
High-YieldNEET PG
In tropical pulmonary eosinophilia, the FEV1/FVC ratio <0.70 defines the obstructive phenotype; this reversible obstruction is the primary target of diethylcarbamazine therapy and normalizes within 3 weeks of treatment.
