Abstract and Introduction
Abstract
Purpose of review Although cough is one of the defining symptoms of asthma, wheeze, chest tightness and breathlessness have generally received more attention. The impact of coughing for patients may be more important than currently appreciated and has been rated more troublesome than wheeze, chest tightness or disturbance of sleep.
Recent findings Studies objectively measuring cough in asthma reveal that cough frequencies vary from those similar to healthy volunteers to cough counts comparable to patients presenting with chronic cough, but the potential triggers for cough in asthma are poorly understood. This review discusses our current knowledge of cough in asthma, potential mechanisms that may provoke coughing, the effect of current treatments and possible future therapeutics.
Summary Cough in some asthma patients is a significant problem, deserving further attention in both clinical practice and clinical research.
Introduction
Cough is one of the defining symptoms of asthma and although as such is frequently used in the diagnosis and monitoring of asthma, the symptoms of wheeze, chest tightness and breathlessness have generally received more attention. Some patients with asthma present with cough as an isolated troublesome symptom and so-called cough-variant asthma is recognized as one of the three commonest causes of chronic cough alongside rhinosinusitis (or upper airways cough syndrome) and gastroesophageal reflux disease. Why in some individuals asthma leads to such profound coughing but not significant wheeze is unclear.
The importance of cough in patient presenting with cough-variant asthma goes without question; however, the importance of this common symptom in patients with classical asthma may have been underestimated. A study by Osman et al. performed a conjoint analysis of patients' symptom weightings in asthma and surprisingly found that cough and breathlessness were rated more troublesome than wheeze, chest tightness or disturbance of sleep. In this study, cough was the most troublesome symptom and patients were willing to trade higher levels of other symptoms for a reduction in coughing. There are a number of potential explanations for this: perhaps cough responds less well to current medications than wheeze or breathlessness; cough is a distinct, easily identified problem and may correlate closely with other symptoms; and in some patients, cough is a dominant severe symptom and, therefore, results in the significant psychosocial and physical complications described in patients presenting with chronic cough. A recent study examined cough-specific quality of life in patients attending a general respiratory outpatient clinic and did not find significant differences in this setting between patients who had presented with asthma, chronic obstructive pulmonary disease bronchiectasis or even chronic cough.
In addition to its importance to patients, some evidence from epidemiological studies suggests that chronic cough may predict poor outcomes in asthma. In a study that followed a cohort of asthma patients over a 9-year period, worsening of cough had the highest predictive weight for severe asthma.
The present review summarizes our current knowledge of the mechanisms underlying cough in asthma, the effectiveness of existing treatments and the potential targets for future treatments to interrupt the cough reflex in asthma.