| Definition |
- Self-limited inflammation of the large airways (bronchi) of the lower respiratory tract
- Characterized primarily by cough lasting 1 to 3 weeks
- Distinguished clinically by the absence of pneumonia (no consolidation)
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| Cause (Etiology) |
- Viral (>90%): Influenza A/B, Parainfluenza, RSV, Coronavirus, Rhinovirus, Adenovirus
- Bacterial (<10%): Mycoplasma pneumoniae, Chlamydia pneumoniae, Bordetella pertussis (Whooping cough)
- Non-Infectious: Inhalation of irritants (smoke, dust, chemical fumes)
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| Result (Functional Effect) |
- Hypersensitivity of the cough reflex
- Transient bronchial hyperresponsiveness (reversible airflow obstruction)
- Impaired mucociliary clearance
- V/Q mismatch (mild) due to mucus plugging
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| Structural Result (Morphologic Effect) |
- Hyperemia and edema of the mucous membranes
- Desquamation (shedding) of the superficial ciliated epithelium
- Infiltration of the bronchial wall by inflammatory cells (lymphocytes, neutrophils)
- Hypersecretion of mucus
- Note: Unlike chronic bronchitis, changes are reversible and do not lead to permanent remodeling
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| Pathophysiology |
- Inoculation of respiratory epithelium by the pathogen
- Release of inflammatory cytokines (IL-6, IL-8, TNF-alpha)
- Up-regulation of mucin genes leading to increased phlegm production
- Direct epithelial damage exposes sub-epithelial vagal receptors → persistent cough
- Smooth muscle contraction (bronchospasm) in susceptible individuals
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| Diagnosis |
- Clinical Diagnosis: Based on history (cough >5 days) and physical exam
- Rule out Pneumonia: Absence of tachycardia (>100 bpm), tachypnea (>24), fever (>38°C), and focal rales/egophony
- Chest X-ray: Only indicated if vital signs are abnormal or physical exam suggests consolidation (to rule out pneumonia)
- Procalcitonin: Sometimes used to distinguish viral vs. bacterial etiology
- Microbiology: Viral or bacterial cultures/PCR generally not indicated for uncomplicated cases
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| Clinical |
- Cough: The hallmark symptom; dry or productive. Can persist for 1–3 weeks
- Sputum: Clear, white, yellow, or green (Note: color does not reliably predict bacterial infection)
- Systemic: Mild fever (rarely high), malaise, headache
- Chest: Retrosternal burning pain on inspiration; wheezing may be present
|
| Imaging |
Chest X-ray
- Usually Normal: The primary role is to verify the absence of parenchymal consolidation (pneumonia)
- Bronchial Cuffing: May see subtle thickening of bronchial walls
CT Chest (Not routinely indicated)
- Would show diffuse bronchial wall thickening
- No focal consolidation or ground-glass opacity
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| Treatment (Rx) |
- Supportive Care: Mainstay of treatment (rest, hydration)
- Antibiotics: Generally NOT indicated (most cases are viral); risks usually outweigh benefits
- Antitussives: Dextromethorphan or guaifenesin for symptom relief
- Bronchodilators: Beta-agonists (Albuterol) only if wheezing/airflow obstruction is present
- Analgesics: NSAIDs or Acetaminophen for chest pain/malaise
- Education: Reassure patient that cough may persist for up to 3 weeks (“post-viral cough”)
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