40 Cough¶

Chapter 40 | Cough: Pathophysiology, Evaluation, and Management

KEY CLINICAL POINTS¶

Cough is a protective reflex but can cause complications like rib fractures, urinary incontinence, and respiratory compromise.
Chronic cough (>8 weeks) is often due to asthma, GERD, postnasal drip, or eosinophilic bronchitis.
Impaired cough is caused by respiratory muscle weakness, chest wall pain, or structural airway abnormalities.
Diagnostic evaluation includes chest radiography, sputum analysis, and esophageal pH monitoring.
Treatment depends on etiology: inhaled corticosteroids for asthma, PPIs for GERD, and antihistamines for rhinosinusitis.

1. DEFINITION & OVERVIEW¶

Cough is a protective reflex that clears airway secretions but can become pathological. It may be acute (<3 weeks), subacute (3–8 weeks), or chronic (>8 weeks). Chronic cough is often due to asthma, GERD, postnasal drip, or eosinophilic bronchitis. Impaired cough (Table 40-1) is a critical factor in respiratory infections and atelectasis.

Table 40-1 Causes of Impaired Cough and Airway Clearance¶

Respirat ory Muscle Weakne ss	Chest W all/Abdo minal Pain	Chest Wall Def ormity	Impaire d Glottic Closure	Central Respirat ory Dep ression	Abnorm al Secre tions	Ciliary Dysfunc tion	Tracheo broncho malacia	Bronchi ectasis	Trachea l/Bronc hial Ste noses
	Chest wall pain	Severe k yphoscol iosis	Tracheo stomy	Anesthe sia/sedat ion	Viscous secretio ns (CF)	Primary ciliary dy skinesia	Tracheo malacia	Bronchie ctasis	Stenose s

1.1 Protective Function and Complications¶

Cough generates intrathoracic pressures up to 300 mmHg to expel secretions. Excessive coughing can cause emesis, syncope, rib fractures, and worsen hernias or back pain. It may also lead to urinary incontinence and social impairment.

1.2 Clinical Significance¶

Cough is a common reason for medical consultation. Persistent cough without other symptoms may indicate serious conditions like lung cancer, sarcoidosis, or tuberculosis. It is often a clue to underlying respiratory, cardiovascular, or gastrointestinal disease.

2. EPIDEMIOLOGY¶

Chronic cough is common, with 10–20% of adults experiencing it. Risk factors include smoking, GERD, asthma, and ACE inhibitor use. It is more prevalent in women and often occurs in winter months. Postviral tussive syndrome is a common subacute cause.

2.1 Demographics¶

Chronic cough is more common in women and long-term smokers. Postnasal drip and ACE inhibitor-induced cough are prevalent in adults, while cough-variant asthma is more common in children.

2.2 Risk Factors¶

Smoking, GERD, asthma, rhinosinusitis, and ACE inhibitor use are major risk factors. Postnasal drainage and airway hyperresponsiveness increase susceptibility to chronic cough.

3. ETIOLOGY & PATHOPHYSIOLOGY¶

Cough is initiated by chemical or mechanical stimuli via TRP channels and P2X3 receptors. The reflex involves coordinated muscle contractions and neural pathways. Chronic cough may result from hypersensitivity, neurogenic inflammation, or abnormal sensory signaling.

3.1 Mechanisms of Cough¶

Cough is triggered by sensory receptors in the airways, pharynx, and esophagus. Afferent signals are transmitted via A δ and C fibers to the nucleus tractus solitarius. Efferent pathways involve expiratory muscles and vocal cord adduction. Chronic cough may result from hypersensitivity of sensory nerves, neurogenic inflammation, or abnormal airway secretions. Eosinophilic bronchitis and cough hypersensitivity syndrome are characterized by exaggerated reflex responses.

4. CLINICAL FEATURES¶

Acute cough is often due to infections or irritants. Chronic cough is associated with asthma, GERD, or postnasal drip. Dry, irritating cough may persist after infections. Productive cough is common in bronchitis or COPD. Cough may worsen with lying down or talking.

4.1 Symptom Patterns¶

Acute cough (<3 weeks) is typically infectious. Subacute cough (3–8 weeks) follows viral infections. Chronic cough (>8 weeks) is often due to asthma, GERD, or eosinophilic bronchitis. Dry cough is common in postviral syndromes.

4.2 Physical Findings¶

Physical exam may reveal wheezing, crackles, rhinitis, or nasal polyps. Postnasal drainage is suggested by throat clearing or mucoid secretions. GERD may present with retrosternal burning or hoarseness.

5. DIFFERENTIAL DIAGNOSIS¶

Differential diagnosis includes asthma, GERD, postnasal drip, bronchiectasis, and lung cancer. Cough-variant asthma is diagnosed by response to bronchodilators. Eosinophilic bronchitis is characterized by sputum eosinophilia without airflow obstruction.

5.1 Common Causes¶

Asthma (cough-variant), GERD, rhinosinusitis, postnasal drip, bronchiectasis, and ACE inhibitor-induced cough are leading causes. Chronic bronchitis presents with early-morning productive cough.

5.2 Red Flags¶

Persistent cough with hemoptysis, weight loss, or night sweats may indicate malignancy or tuberculosis. Unexplained chronic cough requires evaluation for sarcoidosis or vasculitis.

6. INVESTIGATIONS & DIAGNOSIS¶

Chest radiography is essential for chronic cough. Sputum analysis, esophageal pH monitoring, and pulmonary function tests help identify asthma or GERD. Flow-volume curves show cough-induced expiratory spikes.

6.1 Diagnostic Tests¶

Chest X-ray, sputum culture, esophageal pH monitoring, and spirometry are key. Bronchoscopy may be needed for suspected malignancy or bronchiectasis. Cough-induced flow-volume curves demonstrate high expiratory flows.

6.2 Criteria for Diagnosis¶

Cough-variant asthma is diagnosed by variable airflow obstruction on spirometry or bronchoprovocation. Eosinophilic bronchitis is confirmed by sputum eosinophilia >3% without bronchial hyperresponsiveness.

7. MANAGEMENT & TREATMENT¶

Treatment is etiology-driven: inhaled corticosteroids for asthma, PPIs for GERD, and antihistamines for rhinosinusitis. Cough hypersensitivity syndrome may require antitussives. ACE inhibitors should be discontinued if cough is suspected.

7.1 Pharmacologic Therapy¶

Inhaled corticosteroids (ICS) for asthma, PPIs for GERD, antihistamines for rhinitis, and antitussives (dextromethorphan) for non-productive cough. ICS may also treat eosinophilic bronchitis.

7.2 Non-Pharmacologic Approaches¶

Nasal saline irrigation, positional therapy (elevated sleep), and dietary modifications for GERD. Cough-assist devices may improve secretion clearance in patients with impaired cough.

8. PROGNOSIS & COMPLICATIONS¶

Chronic cough is often self-limiting but may persist for months. Complications include sleep disturbance, social isolation, and respiratory muscle fatigue. Untreated GERD or asthma may lead to progressive lung disease.

8.1 Long-Term Outcomes¶

Most cases resolve with targeted therapy. Cough hypersensitivity syndrome may require prolonged management. Persistent cough without identifiable cause may indicate underlying systemic disease.

8.2 Complications¶

Excessive coughing can cause rib fractures, urinary incontinence, and muscle strain. Chronic cough in GERD or asthma may lead to progressive airway damage.

9. SPECIAL CONSIDERATIONS¶

Pregnancy: Avoid NSAIDs and antitussives. Pediatrics: Cough-variant asthma is common in children. Elderly: Consider aspiration risk and drug interactions. ACE inhibitors should be discontinued in patients with suspected cough-related etiology.

9.1 Pregnancy¶

Avoid NSAIDs and antitussives. Use antihistamines cautiously. Monitor for aspiration risk in patients with GERD.

9.2 Pediatrics¶

Cough-variant asthma is common in children. Postviral tussive syndrome is a frequent cause of subacute cough. Avoid ACE inhibitors in children due to risk of angioedema.

10. KEY POINTS & CLINICAL PEARLS¶

Chronic cough >8 weeks is often due to asthma, GERD, or postnasal drip.
Impaired cough is a critical factor in respiratory infections and atelectasis.
ACE inhibitor-induced cough is dose-independent and requires medication discontinuation.
Cough-variant asthma responds to inhaled corticosteroids and bronchodilators.
Esophageal pH monitoring is essential for diagnosing reflux-related cough.