Methacholine inhalational challenge in the evaluation of chronic cough in children.

The medical records of 58 children (age range, 7 to 16 years) who presented with chronic cough were retrospectively analyzed to determine the value of methacholine (MCH) bronchial challenge in reaching a specific diagnosis. Baseline lung function tests were normal in all subjects, apart from an elevated residual volume/total lung capacity ratio (RV/TLC) in 11 patients, and a reduced midexpiratory flow rate (FEF25-75) in five of these patients. Thirty-one patients had a positive response to MCH, but these patients could not be identified on the basis of clinical criteria or spirometric parameters. MCH-positive patients did have a significantly higher RV/TLC than did MCH-negative patients. Twenty-seven of the 31 MCH-positive patients responded to a trial of bronchodilator therapy (albuterol/theophylline), confirming the diagnosis of cough variant asthma in these patients. We conclude that children with chronic cough should be considered for methacholine challenge in order to identify patients who are likely to benefit from specific bronchodilator therapy.