Long-term prognosis of chronic cough: a prospective, observational cohort study

Abstract

Background: The long-term prognosis of chronic cough and its determinants need to be clarified.

Methods: This is a prospective, observational cohort study. Eighty-nine unselected subjects with chronic (> 8 weeks' duration) cough were carefully investigated: Clinical examination, symptom questionnaire, Leicester Cough Questionnaire (LCQ), skin prick tests, ambulatory peak expiratory flow monitoring, spirometry before and after 0.4 mgs of salbutamol, exhaled nitric oxide concentration measurement, hypertonic saline cough provocation test, and histamine bronchial provocation test. After five years, a letter was sent to the subjects containing questions about continuation of cough, smoking, indoor exposures, presence of co-morbidities, and current medication. It also contained LCQ and Cough Clinic diagnostic questionnaire. Sixty-eight subjects (76%) responded.

Results: At five years, continuing regular cough was present in 31 (46%) of the subjects and continuing impairment in cough-related quality of life (less than 1.3 points' improvement in LCQ) in 32 (47%). Continuing regular cough was associated with presence of chronic rhinitis or esophageal reflux disease, baseline mild airway responsiveness to histamine, and baseline strong cough responsiveness to hypertonic saline. Continuing impairment in cough-related quality of life was associated with high body mass index, absence of atopy, absence of pets, and high number of background disorders (esophageal reflux disease, asthma, or chronic rhinitis).

Conclusions: Almost half of subjects with chronic cough suffered of the disorder at five years from initial assessment. Several possible determinants of poor prognosis could be identified.

Keywords: Asthma; Chronic cough; Cough; Esophageal reflux disease; Rhinitis.

Fig. 1

The flow chart of the study. Study A, see reference [8]. Study B, see reference [9]

Fig. 2

A Venn diagram showing the co-existence of chronic cough background disorders in the 68 subjects who responded to the follow-up letter

Fig. 3

The proportion of subjects who suffered from continuing regular cough at five years’ follow-up related to the number of self-reported background disorders (esophageal reflux disease, asthma, or chronic rhinitis). Eighteen subjects reported no background disorders, 25 reported one disorder, 17 reported two disorders, and 8 reported three disorders. P = 0.03 between the groups (Chi-square test), p = 0.007 for the trend between the number of background disorders and continuing cough (univariate logistic regression analysis)

Fig. 4

The change in Leicester cough questionnaire (LCQ) total score at follow-up in relation to the subjects’ body mass index (BMI) at initial assessment. An increase in LCQ total score indicates an improvement in the cough-related quality of life. The lower boundary of the box indicates the 25th percentile, a line within the box marks the median, and the higher boundary indicates the 75th percentile. The error bars above and below the box indicate the 90th and 10th percentiles. P < 0.001 between the groups (unpaired T-test)