Cough related to swallowing in asthma patients

BACKGROUND: Occurrence of cough during swallowing is common among asthma patients, but has not been investigated in detail. OBJECTIVE: We conducted an observational study to determine the prevalence of swallowing-related cough (SRC) and its characteristics in asthma patients. METHODS: Asthma patients attending our outpatient department between May 2005 and April 2007 were interviewed to investigate if they had ever experienced SRC, as well as postnasal drip or heartburn and cough related to these conditions. RESULTS: Among 417 patients who completed the questionnaire, 121 patients (29.0%) had experienced SRC. Spicy and sour foods were the most frequent tussigenic foods, causing cough in 76.0% and 53.7% of the 121 patients, respectively. In patients without SRC, the prevalence rates of postnasal drip and postnasal drip-induced cough were 35.8% (106 of 296) and 7.8% (23 of 296), respectively. The corresponding prevalence rates in patients with SRC were 50.4% (61 of 121) and 37.2% (45 of 121), which were both significantly higher than in patients without cough (p = 0.006 and p < 0.001 respectively). In patients without SRC, the prevalence rates of heartburn and heartburn-induced cough were 22.2% (66 of 296) and 2.4% (7 of 296), respectively. The corresponding prevalence rates in patients with SRC were 45.5% (55 of 121) and 16.5% (20 of 121), with both being significantly higher than in patients without cough (p = 0.002 and p < 0.001, respectively). CONCLUSION: SRC was frequent in asthma patients, and was closely related to postnasal drip and heartburn. Irritable larynx is one of the possible underlying mechanisms of SRC. This study was registered with the University Hospital Medical Information Network clinical trials registry (registration number: UMIN000017426).