Non-invasive monitoring of bronchial inflammation in asthma

The present consensus on the diagnosis and treatment of asthma relies on symptoms and lung function measurements for the monitoring of disease severity. Even though this probably remains the cornerstone of asthma management, the rapidly increasing insight into the pathogenesis and pathophysiology of the disease is presently leading to the development of more direct measurements of airway inflammation, which may provide potentially relevant information on its clinical course and prognosis. However, at present none of these has sufficiently been validated for current use in monitoring patients with asthma. First, there are new ways of looking at symptoms and lung function. Careful measurements of symptoms by visual analogue scale (VAS) are suggesting that inflammatory activity within the airways can be subjectively perceived, a sensitivity which may be blunted in patients with brittle asthma. In addition, modern physiological parameters, such as the degree of bronchodilatation following a deep breath (M/P-ratio), are strongly associated with airway inflammation. Second, there are multiple cellular and/or soluble markers of inflammation in peripheral blood (using PCR, in situ hybridization, flow cytometry, or circulating mediators and cytokines) and in urine (LTE4, EPX). Recently this has been extended by similar measurements in hypertonic saline-induced sputum (cell differentials and specific stainings on cytospins, flow cytometry, and levels of e.g. ECP, IL-5, IL-8). Finally, mediators and cytokines in the condensate of exhaled air (H2O2, leukotrienes, IL-5?) as well as exhaled NO are currently under evaluation. Adding such markers of airway inflammation as guides in asthma therapy is potentially useful. As a first step towards such a new approach we have recently shown that adding the reduction of airway hyperresponsiveness to the aims of asthma therapy leads to a better clinical as well as histological outcome after two years of treatment. In conclusion, there are new and exciting perspectives in the monitoring of disease severity in asthma in the future. Longitudinal studies presently ongoing will elucidate which parameter is potentially most useful in guiding asthma management.