How should one investigate a chronic cough?

A chronic cough (ie, a cough lasting more than 8 weeks¹) has many possible causes. Physicians should use a structured diagnostic approach based on observing the clinical picture, trying therapy for the likely cause, obtaining targeted investigations, and referring to a specialist when needed (Figure 1).

To begin, obtain a clinical history, perform a physical examination, and order a chest radiograph.

In the history, look for exposure to environmental irritants such as tobacco smoke, allergens, or dust, or medications such as angiotensin-converting enzyme (ACE) inhibitors or oxymetazoline (Afrin). If a potential irritant is present, it should be avoided or stopped immediately.^1–3 If the cough improves partially or fully when exposure to the irritant is stopped, this supports a diagnosis of chronic bronchitis or, in the case of ACE inhibitors, ACE-inhibitor-induced cough. The character of the cough (eg, paroxysmal, loose, dry, or productive¹) has not been shown to be diagnostically useful or specific.

If the chest radiograph is abnormal, then the diagnostic inquiry should be guided by the abnormality. Abnormalities that cause cough include bronchogenic carcinoma, sarcoidosis, and bronchiectasis. If the radiograph is normal, then upper airway cough syndrome, asthma, gastroesophageal reflux disease (GERD), chronic bronchitis, or nonasthmatic eosinophilic bronchitis is more likely.

COMMON CAUSES OF CHRONIC COUGH

The most common causes of chronic cough, accounting for 95% of cases, are chronic bronchitis due to environmental irritants, upper airway cough syndrome, GERD, asthma, nonasthmatic eosinophilic bronchitis, and bronchiectasis (Table 1).^1–8

Chronic bronchitis

As noted above, a history of exposure to an irritant suggests this diagnosis.

Upper airway cough syndrome

Upper airway cough syndrome (formerly known as postnasal drip) is due to chronic upper respiratory tract irritation and hypersensitivity of cough receptors.^3,4 Sources of irritation vary and include sinusitis and any form of rhinitis: allergic and nonallergic, postinfectious, environmental irritant-induced, vasomotor, and drug-induced.

Patients complain of postnasal drip or frequent clearing of the throat. On physical examination one can see mucus in the oropharnyx or a cobblestone appearance. However, these symptoms and signs are not specific and may be absent.

A therapeutic trial is warranted, but be aware that different rhinitides respond to specific treatments:

• Histamine-mediated or allergic rhinitis will respond to allergen avoidance, new-generation antihistamines such as loratadine (Claritin), mast cell stabilizers such as cromolyn (Intal), and intranasal glucocorticoids such as fluticasone (Flovent).^4,5
• Nonhistamine-mediated rhinitides (the common cold and perennial nonallergic rhinitis) respond to older-generation antihistamines such as diphenhydramine (Benadryl) and decongestant combinations. If these cannot be used, intranasal glucocorticoids and ipratropium (Atrovent) are alternatives.
• Vasomotor rhinitis will respond to intranasal ipratropium 0.3% for 3 weeks and then as required.
• Postinfective rhinitis, ie, a cough that began as severe bronchitis, would warrant an antihistamine-decongestant combination.

With adequate treatment, the cough should improve after 1 to 2 weeks; if rhinosinus symptoms persist, consider bacterial sinusitis and obtain radiographs of the sinuses. If imaging shows mucosal thickening (> 5 mm) or an air-fluid level, treat with decongestants and antibiotics for 3 weeks.^1,4,5