A 52-year-old woman presents to the respiratory clinic with a 4-month history of chronic dry cough. She denies wheeze, dyspnea, or nocturnal symptoms. Physical examination is unremarkable. Spirometry shows FEV1 92% predicted, FVC 95% predicted, and FEV1/FVC ratio 0.78. Methacholine challenge test is negative (PC20 > 16 mg/mL). Induced sputum analysis reveals eosinophils 8% of nonsquamous cells. The clinical and functional profile shown by the pattern marked **A** in the diagram is most consistent with which diagnosis?
A. Atopic cough with lymphocytic airway inflammation
B. Cough-variant asthma
C. Occupational asthma with fixed airflow obstruction
D. Non-asthmatic eosinophilic bronchitis (NAEB)
Explanation
Why Non-asthmatic eosinophilic bronchitis (NAEB) is right
The clinical presentation and diagnostic triad shown in pattern A — normal spirometry (FEV1/FVC 0.78, no obstruction), negative methacholine challenge (PC20 > 16 mg/mL, no bronchial hyperresponsiveness), and sputum eosinophilia (8% > 3%) — are the pathognomonic diagnostic pillars of NAEB as first described by Gibson et al. (Lancet 1989). This syndrome accounts for 10–30% of chronic cough cases in cough clinics. The absence of variable airflow obstruction and bronchial hyperresponsiveness distinguishes NAEB from asthma, despite the presence of eosinophilic airway inflammation. Inhaled corticosteroids produce dramatic cough suppression within 1–4 weeks.
Why each distractor is wrong
Cough-variant asthma: While it also presents with chronic cough and sputum eosinophilia, cough-variant asthma is defined by a POSITIVE methacholine challenge (PC20 < 8 mg/mL) and often reversible airflow obstruction. This patient's negative methacholine challenge excludes this diagnosis.
Atopic cough with lymphocytic airway inflammation: Atopic cough is characterized by sputum lymphocytosis and absence of eosinophilia. This patient has sputum eosinophilia (8%), making this diagnosis incompatible.
Occupational asthma with fixed airflow obstruction: Fixed airflow obstruction would show a reduced FEV1/FVC ratio (< 0.70) and abnormal flow-volume loop. This patient has normal spirometry with FEV1/FVC 0.78, ruling out fixed obstruction.
High-YieldNEET PG
NAEB = chronic cough + sputum eosinophilia (>3%) + normal spirometry + negative methacholine challenge; responds dramatically to inhaled corticosteroids.
Gibson PG et al., Lancet 1989; Brightling CE, Chest 2006
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