Background: Persistent cough is a common clinical problem. Despite thorough investigation and empirical management, a considerable proportion of those people with subacute and chronic cough have unexplained cough, for which treatment options are limited. While current guidelines recommend inhaled corticosteroids (ICS), the research evidence for this intervention is conflicting.
Objectives: To assess the effects of ICS for subacute and chronic cough in adults.
Search methods: We searched the Cochrane Airways Group Register of Trials, Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE and ClinicalTrials.gov in December 2012 and conducted handsearches.
Selection criteria: Two authors independently assessed all potentially relevant trials. All published and unpublished randomised comparisons of ICS versus placebo in adults with subacute or chronic cough were included. Participants with known chronic respiratory disease and asthma were excluded. Studies of cough-variant asthma and eosinophilic bronchitis were eligible.
Data collection and analysis: Two authors independently extracted data pertaining to pre-defined outcomes. The primary outcome was the proportion of participants with clinical cure or significant improvement (over 70% reduction in cough severity measure) at follow up (clinical success). The secondary outcomes included proportion of participants with clinical cure or over 50% reduction in cough severity measure at follow up, mean change in cough severity measures, complications of cough, biomarkers of inflammation and adverse effects. We requested additional data from study authors.
Main results: Eight primary studies, including 570 participants, were included. The overall methodological quality of studies was good. Significant clinical heterogeneity resulting from differences in participants and interventions, as well as variation in outcome measures, limited the validity of comparisons between studies for most outcomes. Data for the primary outcome of clinical cure or significant (> 70%) improvement were available for only three studies, which were too heterogeneous to pool. Similarly, heterogeneity in study characteristics limited the validity of meta-analysis for the secondary outcomes of proportion of participants with clinical cure or over 50% reduction in cough severity measure and clinical cure. One parallel group trial of predominantly chronic cough with 'cough-variant asthma' identified a significant treatment effect and contributed to the majority of statistical heterogeneity for these outcomes. While ICS treatment resulted in a mean decrease in cough score of 0.34 standard deviations (SMD -0.34; 95% CI -0.56 to -0.13; 346 participants), the quality of evidence was low. Heterogeneity also prevented meta-analysis for the outcome of mean change in visual analogue scale score. Meta-analysis was not possible for the outcomes of pulmonary function, complications of cough or biomarkers of inflammation due to insufficient data. There was moderate quality evidence that treatment with ICS did not significantly increase the odds of experiencing an adverse event (OR 1.67; 95% CI 0.92 to 3.04).
Authors' conclusions: The studies were highly heterogeneous and results were inconsistent. Heterogeneity in study design needs to be addressed in future research in order to test the efficacy of this intervention. International cough guidelines recommend that a trial of ICS should only be considered in patients after thorough evaluation including chest X-ray and consideration of spirometry and other appropriate investigations.