What are the primary differential diagnoses to consider in a pediatric patient presenting with a wet cough?

Differential Diagnoses for Pediatric Wet Cough

When a child presents with a wet cough, the primary differential diagnoses depend critically on duration: acute wet cough (<4 weeks) is most commonly viral upper respiratory infection or community-acquired pneumonia, while chronic wet cough (>4 weeks) is most commonly protracted bacterial bronchitis (PBB), with bronchiectasis, aspiration syndromes, and retained foreign body as important alternative diagnoses. 1

Duration-Based Classification

Acute Wet Cough (<4 weeks)

• Viral upper respiratory infection - the most common cause, typically self-limiting and requiring no specific treatment 2
• Community-acquired pneumonia - requires identification through clinical features (fever, tachypnea, respiratory distress) and chest radiograph 2
• Inhaled foreign body - critical to identify early, presents with sudden onset cough, unilateral wheeze, or asymmetric breath sounds 2

Chronic Wet Cough (>4 weeks)

Most Common:

• Protracted bacterial bronchitis (PBB) - the most frequent cause in specialty settings, characterized by isolated chronic wet cough without specific cough pointers, responsive to 2 weeks of antibiotics targeting Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis 1, 3

Serious Underlying Conditions to Exclude:

• Bronchiectasis - suggested by digital clubbing, chest deformity, failure to thrive, or recurrent PBB episodes 1
• Aspiration lung disease - indicated by coughing with feeding, recurrent pneumonia, or neurodevelopmental concerns 1
• Retained foreign body - consider with sudden onset, unilateral findings, or lack of response to antibiotics 1
• Cardiac anomalies - suggested by exercise intolerance, cyanosis, or heart murmur 1
• Interstitial lung disease - rare, but consider with digital clubbing, hypoxemia, or diffuse radiographic changes 1
• Immunodeficiency - suggested by recurrent infections, failure to thrive, or family history 1

Specific Cough Pointers That Narrow the Differential

The presence of these features indicates "specific cough" requiring targeted investigation rather than empirical antibiotic treatment 1:

• Digital clubbing - suggests bronchiectasis, interstitial lung disease, or cardiac disease 1
• Coughing with feeding - indicates aspiration or swallowing dysfunction 1
• Chest deformity - suggests chronic lung disease or severe asthma 1
• Failure to thrive/growth failure - indicates chronic disease including bronchiectasis, cystic fibrosis, or immunodeficiency 1, 4
• Paroxysmal cough with post-tussive vomiting or inspiratory "whoop" - classic for pertussis, even in vaccinated children due to waning immunity 4

Upper Airway Causes

While controversial, upper airway conditions may present with wet cough 5:

• Upper Airway Cough Syndrome (UACS) - underlying conditions include allergic rhinitis, adenoiditis, and rhinosinusitis, though the diagnosis relies on relatively non-specific clinical criteria 5
• Important caveat: Chronic wet cough should not be assumed to be upper airway disease without careful evaluation, as lower airway bacterial infection (PBB) is more common and requires different treatment 5

Age-Specific Considerations

• Neonates and premature infants - respiratory illness typically manifests as tachypnea, dyspnea, or hypoxemia rather than chronic cough; wet cough in this age group warrants immediate comprehensive evaluation 1
• Young children (<6 years) - cannot reliably expectorate, so "wet cough" describes the loose, self-propagating sound rather than visible sputum production 1

Critical Pitfall to Avoid

Do not dismiss chronic wet cough as "just a viral infection" or "normal childhood cough." Persistent wet cough beyond 4 weeks is never normal and requires systematic evaluation, as early recognition and treatment of PBB prevents progression to irreversible bronchiectasis 1, 6, 7. The relationship between PBB and bronchiectasis represents a clinical continuum where early features are indistinguishable, making prompt diagnosis essential 2.

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