Usefulness of Exhaled Nitric Oxide and Sputum Eosinophils in the long-term control of Eosinophilic Asthma

Background: The aim of the present study was to treat unstable asthma according to exhaled nitric oxide (eNO) and induced-sputum eosinophils (sEos) levels to assess if this strategy is better than the conventional approach based on symptoms and function to achieve asthma control. Methods: Fourteen patients with mild-to-moderate persistent asthma (6 men, 8 women) were recruited. During the recruitment visit, the patients, previously treated for asthma following Global Initiative for Asthma recommendations, underwent clinical evaluation and pulmonary function tests (PFTs). Then, after 4 weeks of washout from inhaled antiinflammatory treatment, the patients underwent a basal visit performing PFTs, challenge test to methacholine, and determination of eNO and sEos counts. These procedures were repeated after 3, 6, and 12 months while the patients were treated with inhaled steroids in a stepwise fashion according to eNO and sEos values. Results: At the end of the study, a significant decrease in eNO and sEos was observed (57.2 32.8 parts per billion [ppb] vs 22.1 10.8 ppb, p < 0.01; and 27.1 27.1% vs 3.7 3.5%, p < 0.01, respectively). A close correlation (r2 0.41, p < 0.01) between the percentage change of eNO and sEos was observed only after 6 months. Patients treated according to the levels of these inflammatory markers had fewer symptoms and fewer exacerbations compared to those the year before when they were conventionally treated. Conclusions: Our results show the usefulness of eNO and sEos for titrating treatment in asthmatic patients in order to achieve better long-term control of the disease. The eNO decrease reflects adequately the reduction of sEos only after 6 months.