Adult-onset asthma: Predictors of clinical course and severity

Adult-onset asthma is a common airway disease that starts during adulthood and is characterized by reversible airway obstruction, bronchial hyperreactivity and chronic airway inflammation. In contrast to childhood onset asthma the clinical course of adult-onset asthma over time is still largely unknown. An important pathophysiologic characteristic is eosinophilic airway inflammation, which plays a role in the severity of the disease. The purpose of this thesis is firstly to examine the diagnostic accuracy of markers of airway eosinophilia, and secondly to identify predictors of the clinical course. In part one, biomarkers for airway eosinophilia were investigated in different adult-onset asthma phenotypes at either high sensitivity or high specificity and in a systematic review and meta-analysis in the general asthma population. Despite a general moderate diagnostic accuracy, biomarkers (blood eosinophils, FeNO) are useful at either low or high biomarker cut-off levels and are not influenced by asthma phenotype. In the future, biomarkers might be useful to identify patients eligible for a specific therapy and to adjust medication dose. Part two describes the clinical course of adult-onset asthma patients during 5 years of follow-up. One in six patients reaches asthma remission, although the chance is <1% in patients with nasal polyps and moderate-severe bronchial hyperresponsiveness. An increase in asthma severity was related to smoking in a dose dependent way. Exacerbations in (ex)smokers and never smokers were related to different types of inflammatory cells. These novel insights into adult-onset asthma can be used to improve care for asthma patients and reduce asthma morbidity.