EXACERBATIONS OF ASTHMA WITHOUT SPUTUM EOSINOPHILIA

Background - Sputum analysis provides a non-invasive method of examini ng the airway secretions of subjects with asthma in order to better un derstand the inflammatory process. Increased proportions of eosinophil s are generally seen in the sputum of subjects with asthma, especially when there is an exacerbation. An unexpected observation in the sputu m of subjects with mild exacerbations of asthma is reported. Methods - Thirty four consecutive subjects with symptoms consistent with a mild exacerbation of asthma were recruited for a treatment study. Inclusio n criteria required persistent symptoms of chest tightness, dyspnoea, or wheezing for two weeks (without spontaneous improvement or alterati on in dose of inhaled corticosteroid) and a forced expiratory volume i n one second (FEV(1)) that was reversible to more than 75% predicted o r known best to ensure the exacerbation was mild. Sputum (spontaneous or induced with hypertonic saline) from all subjects was examined for differential cell counts. Eosinophilic sputum was defined as greater t han or equal to 4% eosinophils on two occasions or >10% eosinophils on ce. Clinical characteristics, sputum differential counts, and measurem ents of airways obstruction were compared between the subjects with an d without sputum eosinophilia. Results - Almost half of the subjects ( 16 of 34) considered to have mildly uncontrolled asthma had no sputum eosinophilia. In comparison with the subjects who had sputum eosinophi lia the non-eosinophilic group had less airways obstruction (FEV(1)% p redicted 88% v 70%) and less severe airways hyperresponsiveness (PC20 methacholine 0.45 mg/ml v 0.13 mg/ml). There was no difference between the groups in the type or prevalence of symptoms, history of recent i nfections, smoking, relevant allergen exposure, or use of inhaled cort icosteroid. Conclusions - Symptoms of mildly uncontrolled asthma are n ot always associated with eosinophilic airways inflammation as measure d by sputum analysis. The causes and treatment of the non-eosinophilic condition require further investigation.