Elsevier

The Lancet

Volume 371, Issue 9621, 19–25 April 2008, Pages 1364-1374
The Lancet

Series
Prevalence, pathogenesis, and causes of chronic cough

https://doi.org/10.1016/S0140-6736(08)60595-4Get rights and content

Summary

Cough is a reflex action of the respiratory tract that is used to clear the upper airways. Chronic cough lasting for more than 8 weeks is common in the community. The causes include cigarette smoking, exposure to cigarette smoke, and exposure to environmental pollution, especially particulates. Diseases causing chronic cough include asthma, eosinophilic bronchitis, gastro-oesophageal reflux disease, postnasal drip syndrome or rhinosinusitis, chronic obstructive pulmonary disease, pulmonary fibrosis, and bronchiectasis. Doctors should always work towards a clear diagnosis, considering common and rare illnesses. In some patients, no cause is identified, leading to the diagnosis of idiopathic cough. Chronic cough is often associated with an increased response to tussive agents such as capsaicin. Plastic changes in intrinsic and synaptic excitability in the brainstem, spine, or airway nerves can enhance the cough reflex, and can persist in the absence of the initiating cough event. Structural and inflammatory airway mucosal changes in non-asthmatic chronic cough could represent the cause or the traumatic response to repetitive coughing. Effective control of cough requires not only controlling the disease causing the cough but also desensitisation of cough pathways.

Introduction

Cough is recognised as a defence reflex mechanism, with three phases: (1) an inspiratory phase; (2) a forced expiratory effort against a closed glottis; (3) opening of the glottis, with subsequent rapid expiration, that generates a characteristic cough sound. Physiologists make the important distinction between cough and the closely related defence expiratory reflex, which does not result in a cough.1 A cough sound allows the clinician to distinguish cough from other symptoms, such as throat-clearing and sneezing; cough usually presents with a series of coughs known as a cough bout. Cough clears the larynx, trachea, and large bronchi of secretions such as mucus, noxious substances, foreign particles, and infectious organisms. Almost everybody has had cough after a common cold, which typically lasts 1–3 weeks. The protective nature of cough is well illustrated by the complications of cough suppression after general anaesthesia, which include retention of airway secretions, and infections. Cough can also be a warning sign of disease, and can cause the patient to seek medical attention, leading to diagnosis. When cough is excessive and chronic, it can be detrimental to the patient with complications such as vomiting, rib fractures, urinary incontinence, syncope, muscle pain, tiredness, and depression.

This Series will focus on chronic cough in adults, which is defined as cough that has lasted for at least 8 weeks, since such cough can present difficulties in diagnosis and management. The second part of this Series will cover management aspects of chronic cough. Previous reviews and guidelines were aimed mainly at the specialist;2, 3, 4 however, this Series provides an up-to-date review not only for the specialist, but also for the non-specialist.

Section snippets

Pathogenesis

Figure 1 shows the anatomy of cough pathways, and figure 2 the regulation and physiology of the enhanced cough reflex. A cough reflex can be triggered by several inflammatory or mechanical changes in the airways, and by inhalation of chemical and mechanical irritants, usually from upper airway sites, especially the larynx, the carina, and other points where the proximal airways branch.5, 6 Sensory nerve receptors responding to these stimuli are defined by their conductive properties as rapidly

Prevalence

The prevalence of cough in many communities in Europe and the USA reported through questionnaire surveys is 9–33% of the population, including young children (table 1).34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 Chronic cough is often related to cigarette smoking.34, 36, 39, 40 Chronic smokers have a prevalence of chronic cough three times as high as people who have never smoked, or as ex-smokers.44 Investigators have also noted associations with asthma, respiratory wheezing, and symptoms of

Conditions associated with chronic cough

Chronic cough can arise in asthma in various clinical settings, and is not always associated with airflow obstruction, wheezing or dyspnoea. Asthma can predominantly present with cough, which is often nocturnal; the diagnosis is supported by the presence of bronchial hyper-responsiveness.75 Elderly people with asthma can also present with a history of chronic cough, with little or no wheezing. Cough is often the symptom most reported by patients with chronic asthma, despite achieving good

Search strategy and selection criteria

We did a detailed appraisal of peer-reviewed publications over the past 10 years with the NCBI PubMed website for English language publications with the keywords: “Cough”, in combination with “treatment”, “asthma”, “postnasal drip”, “eosinophilic bronchitis”, “gastro-oesophageal reflux”, “cigarette smoking”, “guidelines”, “prevalence”, and “infections”. We also had source publications that we have accumulated because of our association with cough treatment and research in the past 15

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