Relationship between exhaled nitric oxide and mucosal eosinophilic inflammation in children with difficult asthma, after treatment with oral prednisolone

Exhaled nitric oxide (FEN,) has been proposed as a noninvasive marker of ai rway inflammation in asthma, and may reflect airway eosinophilia. We examin ed the relationship between FEN, and eosinophilic inflammation in endobronc hial biopsies from 31 children with difficult asthma (mean age [range] 11.9 [6-17] yr), following 2 wk of prednisolone (40 mg/d). Endobronchial biopsy was also performed in seven children without asthma. Biopsy eosinophils we re detected using antibody to major basic protein, and point-counting used to derive an "eosinophit score." FEN. readings and suitable biopsies for an alysis were both obtained in 21 of 31 children with asthma. Adherence to pr ednisolone was demonstrated in 17 of these 21. Within this group, there was a correlation between FEN, and eosinophil score (r = 0.54, p = 0.03). The relationship was strongest in patients with persistent symptoms after predn isolone, in whom FENO > 7 ppb was associated with a raised eosinophil score . For all patients, FENQ < 7 ppb was associated with an eosinophil score wi thin the nonasthmatic range, regardless of symptoms. We propose that FENO i s associated with eosinophilic inflammation in children with difficult asth ma, following prednisolone, and may help in identifying patients in whom pe rsistent symptoms are associated with airway eosinophilia.