Utility of tests used to diagnose asthma, gastroesophageal reflux and upper airway cough syndrome in patients with chronic cough and normal chest radiography

BackgroundDespite the clinical significance of cough, research efforts aimed at improving diagnostic capabilities and developing more effective therapeutic agents have been, to date, disappointing in their limited scope and outcomes. Asthma, gastro-oesophageal reflux disease (GERD) and upper airway cough syndrome (UACS) are common causes for chronic cough with a normal chest X-ray (CXR).AimTo describe the frequency of these three causes in a cohort of outpatients with chronic cough and normal CXR and to identify the diagnostic tests best able to identify the aetiology in the vast majority of cases using the response to specific therapy as a gold standard.MethodsNonsmoking outpatients of both genders who complained of cough for more than 8 weeks and had normal findings on CXR were studied prospectively. All patients were subjected to spirometery (including postbronchodilator reversibility), sinuses CT scan, rhinoscopy, and 24-h esophageal pH monitoring to get “an initial diagnosis”. The assumed causes were confirmed by treating them sequentially. “The final diagnosis” depended on a successful response to therapy.ResultsHundred patients were studied: the laboratory tests established initial diagnoses of asthma, UACS, GERD, or various combinations of these in 78 patients, of those; 35 patients (44.9%) had a single cause, 39 patients (50%) had two causes, and 4 patients (5.1%) had all three causes. After treatment of those 78 patients, the final diagnoses were established as follow: 47 patients (60.3%) has a single cause, 28 patients (35.9%) had two causes and 3 patients (3.8%) had all three causes. There was a good agreement between the laboratory tests and the definite causes (agreement in 65 patients [83%] and discrepancy in 13 patients [17%], k > 0.75). Twelve patients had their diagnoses changed for two causes to a single cause and one patients had the diagnosis changed from three causes to two causes.ConclusionAsthma, UACS, GERD, or some combination of these represent 78% of the causes of chronic cough in our sample. Therefore, these conditions should be considered first during diagnostic evaluation of patients with chronic cough and normal CXR. Inspite of some discrepancy between initial and final diagnoses, the study identifies the group of diagnostic methods best able to identify the cause in the vast majority of cases of chronic cough including sinuses CT scan, rhinoscopy, pulmonary function tests, and esophageal pH monitoring.