Pathophysiology and therapy of chronic cough.

Cough is an essential protective mechanism for the airways and lungs. Cough receptors are situated in the larynx and tracheobronchial tree, and are mediated by rapidly-adapting (irritant) Adelta fibers, although other receptors such as C-fiber receptors may contribute. Cough plasticity and interactions of cough pathways may occur centrally to enhance the cough reflex. The presence of an increased cough reflex as measured by a tussive response to capsaicin or citric acid in patients with a chronic cough indicate that there is sensitisation of the cough reflex. The most common cause of acute cough is that after a common cold, which usually lasts for less than 2 weeks. Cough that persists longer may be due to asthma and its variant forms (cough variant asthma and eosinophilic bronchitis), rhinosinusitis (postnasal drip), gastro-esophageal reflux, bronchiectasis, chronic bronchitis, and angiotensin-converting enzyme (ACE) inhibitor therapy. Chronic persistent cough can contribute to a significant worsening of quality of life measures. Bronchial tumors must be excluded with a chest radiograph. The management of chronic cough includes investigation and treatment of any associated causes, which sometimes leads to control of cough. In a proportion of patients, cough may be idiopathic and remain uncontrolled. Currently-available antitussives such as dextromethorphan or codeine are modestly successful in controlling cough. New antitussives may be developed that act on the sensory receptors or prevent their sensitisation.