Published Online: July 24, 2015
Asthma exacerbations are a leading cause of Emergency Department (ED) visits and hospitalizations, yet little is known regarding their pathophysiology. Questions yet to be elucidated include whether the mechanisms involved in viral-induced asthma exacerbations differ from non-viral-mediated exacerbations, and whether corticosteroids are effective in viral-induced asthma exacerbations which are associated with neutrophilic inflammation.
Malka et al., address these issues in an upcoming issue of The Journal of Allergy and Clinical Immunology: In Practice. Children presenting to the ED with an acute asthma exacerbation requiring a course of oral corticosteroids underwent Polymerase Chain Reaction testing for respiratory viruses, and underwent spirometry and FeNO measurements. After a course of prednisone, FeNO and spirometry was repeated. Fifty-six percent of the children had a viral respiratory tract infection with rhinovirus most often identified. At the time of the exacerbation, the subjects’ FEV1 (Forced Expiratory Volume in one second) fell 24% in both groups, while FeNO increased significantly more in the non-viral induced exacerbation group. Patients with rhinovirus infections had the largest increase in FeNO. Following a short course of prednisone, lung function in both groups improved to baseline levels. FeNO levels fell in both groups, with greatest decline in those with viral-induced exacerbations.
This study provides insight into the mechanisms involved in childhood asthma exacerbations. First, there was no difference in the severity of the exacerbation between the groups based on symptoms or lung function, yet the rise in FeNO was greater in those without a viral infection. Second, prednisone was equally effective in improving lung function, and symptoms between the two groups, while the largest reduction FeNO was noted in those with a viral-induced exacerbation. The data suggest that non-viral-mediated asthma exacerbations are more likely to be TH2 driven, as IL-4 and Il-13 are involved in the up-regulation of iNOS (inducible nitric oxide synthase) and increased FeNO levels. Surprisingly, the FeNO levels fall to a greater level in those with viral-induced exacerbations, which are mediated by steroid-unresponsive, neutrophilic inflammation. This suggests that corticosteroid responsive pathways are involved in the pathogenesis of viral-induced asthma exacerbations. It is hoped that larger studies will further our understanding of the mechanisms involved in exacerbations in children with asthma.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.