Chronic cough as a novel phenotype of chronic obstructive pulmonary disease
The chronic bronchitis phenotype of chronic obstructive pulmonary disease (COPD) is characterised by persistent cough and sputum production, and is associated with worse respiratory symptoms, high rates of acute exacerbation and greater disease impact than other phenotypes. However, chronic cough can occur without sputum, and the clinical characteristics of this are not well studied.
Of the enrolled 1,613 COPD patients, over a quarter of whom were current smokers, 23.4% reported chronic cough and 32.4% chronic sputum, while 18.2% had both symptoms. Those with chronic cough were more likely to be younger patients and current smokers; they also exhibited more frequent exacerbations and severe dyspnoea, and poorer quality of life than those without chronic cough. Compared with patients having sputum only, those with cough had only more severe airflow limitation. Chronic cough was an independent risk factor in lower forced expiratory volume in 1 second (FEV1) and diffusing capacity of the lungs for carbon monoxide, but sputum production was not found to be associated with these measurements.
Although the study had several limitations, its findings suggest chronic cough could be more significantly associated with disease severity and poor outcomes than sputum production, warranting further studies.