Multicenter questionnaire study investigating characteristics of adults with unexplained chronic cough versus explained chronic cough

Abstract

Objective: Previously, we reported that older women taking increased numbers of cough medications with increased number and frequency of medical encounters and normal or near-normal lung function more likely had unexplained chronic cough (UCC) versus asthma and/or chronic obstructive pulmonary disease. This study sought to identify clinical risk factors that could differentiate UCC from explained chronic cough (ECC). Methods: A validated electronic questionnaire was distributed to patients with chronic cough (CC) at seven cough centers throughout the United States. The mean ± standard error, frequencies of continuous variables (one-way analysis), and cross-tabulation frequencies for categorical variables (two-way analysis) were calculated. Univariate comparisons between UCC and ECC were performed by using the t-test and nonparametric one-way analysis. Significant determinants of UCC and cough severity were assessed by using multiple logistic regression. Results: A total of 150 patients were enrolled, of whom 29 of 150 were classified as having UCC, and 121 of 150 were classified as having ECC. No significant differences for family history, age, gender, and race, or seasonality differentiated UCC from ECC. Multiple logistic regression revealed the absence of postnasal drip significantly differentiated UCC from ECC (odds ratio 4.8 [95% Confidence Level, 1.6-15.3]). The severity of CC was worse for patients with UCC, patients with chronic bronchitis and/or emphysema, hypertension, ex-smoking history, high body mass index, female gender, education level, and reactivity to more environmental irritants (perfume, p = 0.006; household cleaners, p = 0.01; air fresheners, p = 0.03; cold air, p = 0.007; cigarette smoke, p = 0.05). Conclusion: Patients with UCC more frequently presented with specific demographic features, comorbid characteristics, and more severe cough induced by environmental irritants compared with ECC. These clinical characteristics may be useful for identifying risk factors that can accelerate the diagnosis of UCC.

Figure 1.

A significantly higher BMI (overweight, obese, and extremely obese) was found in 23.3% of the men (n = 35) and 36.7% of the women (n = 55) with UCC, which was statistically significant when compared with a normal BMI in men (*p < 0.05, ****p < 0.0001) and women (####p < 0.0001). Calculated BMI was made by using reported pounds and inches by gender (underweight, <18.5 kg/m²; normal, 18.5–24.9 kg/m²; overweight, 25–29.9 kg/m²; obese, 30–39.9 kg/m²; extremely obese, >40 kg/m²). BMI = Body mass index; UCC = unexplained chronic cough.

Figure 2.

ROC curve for logistic regression model for determinants of CC severity symptoms greater in UCC versus ECC, including being female, having a higher BMI and comorbid chronic bronchitis and/or asthma, hypertension or previous cigarette smoking any time before the last 1 year. ROC = Receiver operator characteristic; CC = chronic cough; UCC = unexplained chronic cough; ECC = explained chronic cough; BMI = body mass index.