Induced sputum: Comparison of postinfectious cough with allergic asthma inchildren

Background: Cough persisting after a respiratory infection Is common in chi ldren and is often managed as asthma, However, little is known about the pa thophysiologic: mechanisms of such cough and how it compares with asthma, Objective: We used the technique of induced sputum to examine the inflammat ory index values associated with persistent cough or allergic asthma in chi ldren. We hypothesized that the sputum from children with persistent postin fectious cough would differ from that of children with allergic asthma in t hat the former would lack eosinophils compared with the latter. Study desig n: Sputum production was induced with hypertonic saline solution in 34 chil dren: 12 with cough persisting for 1 month or more after an apparent respir atory tract infection, not treated with corticosteroid; 11 with untreated a topic asthma, not using inhaled corticosteroid; and 11 with treated atopic asthma using inhaled corticosteroid, Results: The percentage of eosinophils in the sputum of children with cough was significantly lower than in the sputum of children with untreated alle rgic asthma (median 0.5% vs 14.5%, F < .0001), Similarly, the percentage of eosinophils in the sputum of children with asthma treated with inhaled ste roids was significantly lower compared with untreated asthmatic children (1 .5% vs 14.5%, P < .0001). The peripheral blood eosinophils, serum eosinophi l cationic protein, and nasal percent eosinophils of the patients with coug h were also significantly lower than those from patients with untreated ast hma, Methacholine challenge in 6 of the 11 cough patients tested showed mil d-to-moderate hyperresponsiveness, whereas the other 5 had a negative metha choline challenge, Conclusions: Children with persistent postinfectious cough do not have airw ay eosinophilia typical of untreated asthma, Despite the absence of eosinop hilic inflammation, some of the patients with chronic cough had reactive ai rways. These results suggest that postinfectious cough in children has diff erent pathophysiologic features than allergic asthma and probably represent s a different disease.