COUGH

Cough is an important physiologic mechanism that defends against respiratory pathogens and helps to clear the tracheobronchial tree of mucus, foreign particles, and noxious aerosols. Excessive cough is one of the most common symptoms for which patients seek medical care and may represent up to one-third of a pulmonologist's outpatient practice referrals. Persistent severe cough, seen in interstitial lung disease or bronchiectasis, may impair respiration as well as disrupt sleep and social functioning. Bronchospasm (brought on by repetitive forced exhalation), syncope, rib fractures, and urinary incontinence are all potential complications. A reduced or absent cough, seen in some postoperative patients or those with neuromuscular disease, will reduce clearance of secretions and may impair oxygenation.
Cough may be voluntary or involuntary. Involuntary cough is stimulated by vagal afferent receptors in the trachea, especially at the carina, and the larynx but also from others throughout the head and neck. Stimulation of cough receptors may be mechanical, as in cases of aspiration, or irritative.

Clinical Findings
It is important to distinguish acute (< 3 weeks) from chronic cough. Acute cough most commonly follows viral or bacterial upper respiratory tract infection. Within 2 days after onset of the common cold, 85% of untreated patients cough; 26% are still coughing 14 days later; in a few, cough will persist for 6–8 weeks. Many patients with persistent cough following upper respiratory tract infection have underlying asthma. Other causes of acute cough include aspiration, pneumonia, pulmonary embolism, and pulmonary edema.
The most common cause of chronic cough is a low-grade chronic bronchitis secondary to exposure to tobacco smoke, though smokers do not commonly seek medical attention for this problem. Over 90% of nonsmokers presenting for evaluation of chronic cough suffer from postnasal drip, gastroesophageal reflux disease, or asthma (even without other symptoms). Angiotensin-converting enzyme (ACE) inhibitors have become another common cause. In primary care settings, single causes predominate.
The character and timing of chronic cough and the presence or absence of sputum production do not permit an etiologic diagnosis and should not be used as the sole basis for empirical therapy. The history and physical examination should attempt to identify anatomic locations of the afferent limb of the cough reflex in light of the common causes listed above. A nasal discharge, frequent need to clear the throat, and mucoid or mucopurulent secretions in the posterior pharynx suggest postnasal drip. Sinus radiographs may be diagnostic of acute or chronic sinusitis. Wheezing on chest auscultation or airflow obstruction on pulmonary function tests suggest asthma. In cough-variant asthma, methacholine bronchoprovocation testing may be positive in the absence of clinical findings of asthma. Gastroesophageal reflux disease is an important cause of chronic cough but is associated with the fewest clinical clues. Patients may complain of heartburn or regurgitation, but cough may be the only symptom. Barium swallow is specific but insensitive, and esophageal pH monitoring may be necessary. Chest radiographs are best reserved for cough in smokers and patients with hemoptysis or constitutional symptoms such as fever and weight loss.

Treatment
The first step is to eliminate irritant exposures such as tobacco smoke (primary or secondary) and occupational agents and to discontinue medications such as ACE inhibitors or beta-blockers, including eyedrops. Cough due to ACE inhibitors should subside within 1–4 days after discontinuing the medication, though it may take weeks to months. Postnasal drip syndrome due to allergic rhinitis that does not respond to antihistamines should be treated with intranasal steroids. Chronic sinusitis may require prolonged antibiotics directed against Haemophilus influenzae. Cough caused by asthma that does not respond after 2 weeks of bronchodilators and corticosteroids suggests another contributing condition. Cough due to gastroesophageal reflux disease is difficult to treat, since H2 blockers may not be adequate. Most practitioners now initiate antitussive therapy for gastroesophageal reflux disease with proton pump inhibitors. Patients whose cough began after an upper respiratory tract infection usually respond to treatment with an antihistamine-decongestant combination or treatment for asthma.