Cough is the
most frequent symptom of respiratory disease. It is caused by
stimulation of sensory nerves in the mucosa of the
pharynx, larynx, trachea and bronchi. Acute
sensitisation of the normal cough reflex occurs in a number of
conditions, and it is typically induced by changes in air
temperature or exposure to irritants such as cigarette
smoke or perfumes. The characteristics of cough originating at various levels of the respiratory tract are
detailed in The explosive
quality of a normal cough is lost in patients with
respiratory muscle paralysis or vocal cord palsy.
Paralysis of a single vocal cord gives rise to a prolonged, low-pitched,
inefficient ‘bovine’ cough accompanied by hoarseness.
Coexistence of an inspiratory noise (stridor)
indicates partial obstruction of a major airway (e.g.
laryngeal oedema, tracheal tumour, scarring, compression or
inhaled foreign body) and requires urgent
investigation and treatment. Sputum production is common in
patients with acute or chronic cough, and its nature
and appearance can provide clues to the aetiology
Causes of cough
Acute transient
cough is most commonly caused by viral lower
respiratory tract infection, post-nasal drip resulting from rhinitis
or sinusitis, aspiration of a foreign body or
throat-clearing secondary to laryngitis or pharyngitis. When it occurs
in the context of more serious diseases such as
pneumonia, aspiration, congestive heart failure or pulmonary
embolism, it is usually easy to diagnose from other
clinical features. Patients with
chronic cough present more of a diagnostic challenge,
especially when physical examination, chest X-ray and
lung function studies are normal. In this context,
it is most often explained by cough-variant asthma (where
cough may be the principal or exclusive clinical
manifestation), post-nasal drip secondary to nasal or sinus
disease, or gastro-oesophageal reflux with aspiration. Diagnosis of the latter may require ambulatory pH
monitoring or a prolonged trial of antireflux therapy . Between 10 and 15% of patients (particularly
women) taking angiotensin-converting enzyme (ACE)
inhibitors develop a drug-induced chronic cough. Bordetella pertussis infection in
adults can also result in protracted cough and should be suspected in
those in close contact with children. While most
patients with a bronchogenic carcinoma have an
abnormal chest X-ray on presentation, fibreoptic bronchoscopy or
thoracic CT is advisable in most adults (especially
smokers) with otherwise unexplained cough of recent
onset, as this may reveal a small endobronchial tumour or
unexpected foreign body .In a small percentage of
patients, dry cough may be the presenting feature of interstitial lung disease.