Chronic cough persisting for two months or more that remains unexplained after extensive investigations is a common clinical problem. The purpose of this study was to determine whether such cough is associated with otherwise asymptomatic gastro-oesophageal reflux. Thirteen patients with chronic persistent cough that was unexplained after a standard diagnostic assessment were identified. All were non-smokers. The mean (SE) duration of cough was 17.8 (8.0) months. Ten had never had reflux symptoms and three had had mild symptoms only after the onset of the cough. All the patients completed standardised cough diary cards for eight weeks and underwent 24 hour ambulatory oesophageal pH monitoring. A reflux episode was defined as a fall in oesophageal pH to below 4.0. Nine control subjects were matched for age, lung function, and body mass index. The patients experienced significantly more episodes of reflux per 24 hours than the controls (115.8 (SE 31.7) versus 4.7 (1.4) and longer reflux episodes (15.5 (5.8) versus 1.7 (0.5) minutes), and the oesophageal pH was below 4.0 considerably longer (84.5 (20.2) versus 3.8 (1.3) minutes). Cough occurred simultaneously with 13% (2.2%) of reflux episodes and within five minutes in another 35% (5.8%) of episodes, whereas gastro-oesophageal reflux occurred simultaneously with 78% (5.5%) of cough episodes and within five minutes in another 12% (2.3%) of episodes. It is concluded that chronic persistent cough that remains unexplained after a standard diagnostic assessment is associated with otherwise asymptomatic gastro-oesophageal reflux. It is suggested that a self perpetuating mechanism may exist whereby acid reflux causes cough via a local neuronal oesophageal-tracheo-bronchial reflex, and the cough in turn amplifies reflux via increased transdiaphragmatic pressure or by inducing transient lower oesophageal sphincter relaxation. Further study of this mechanism and the role of specific antireflux treatment in chronic persistent cough is warranted.
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