What are the differential diagnoses and initial evaluation for a pediatric patient presenting with a brassy, harsh, metallic‑sounding cough?

Differential Diagnoses for Pediatric Brassy Cough

A brassy cough in a pediatric patient should immediately raise suspicion for tracheomalacia, as this is the primary validated association with a sensitivity of 0.57 and specificity of 0.81. 1

Primary Differential: Tracheomalacia

• Tracheomalacia is the most evidence-based diagnosis when a child presents with a characteristic brassy, harsh, metallic-sounding cough, with documented interobserver agreement of 0.79 (95% CI: 0.73-0.86) 1
• The brassy quality reflects turbulent airflow through a collapsible trachea that impedes secretion clearance 2
• Tracheomalacia often coexists with gastroesophageal reflux (GER), which can exacerbate symptoms 2
• Symptoms typically include a homophonous wheeze or "tracheal cough" that suggests central airway obstruction 2

Other Intrathoracic Airway Lesions to Consider

• Congenital vascular anomalies causing external tracheal compression present with persistent cough in 75% of cases 1
• Bronchomalacia and other structural airway abnormalities were found in 46% of children with chronic cough in tertiary centers 1
• These lesions are frequently misdiagnosed as asthma, leading to inappropriate treatment 1, 3

Additional Differential Diagnoses

• Asthma can present with wheeze and intrathoracic airway involvement, though isolated brassy cough is less typical 1
• Foreign body aspiration must be excluded, particularly in younger children, as delayed diagnosis causes permanent lung damage 1
• Pertussis presents with paroxysmal cough, post-tussive vomiting, and characteristic "whoop" sound rather than brassy quality 4
• Cystic fibrosis and primary ciliary dyskinesia cause chronic productive cough rather than isolated brassy cough 5, 3

Initial Evaluation Approach

History Red Flags

• Age of onset (newborn period suggests tracheomalacia) 2
• Associated symptoms: difficulty feeding, respiratory distress, stridor, or failure to thrive 1, 6
• Positional changes in cough severity (worse when supine suggests GER contribution) 2
• Paroxysmal episodes with post-tussive vomiting (suggests pertussis, not tracheomalacia) 4, 7

Physical Examination Specifics

• Listen for homophonous wheeze (monophonic, fixed-pitch) indicating central airway obstruction rather than peripheral bronchospasm 2
• Assess for stridor (high-pitched inspiratory noise suggests laryngomalacia or severe tracheomalacia) 6
• Evaluate respiratory effort: retractions, tachypnea, oxygen saturation 8
• Check for failure to thrive or growth retardation (suggests chronic underlying disease) 5

Diagnostic Testing Strategy

First-line investigations:

• Airway fluoroscopy can diagnose tracheomalacia in most cases and is available to primary care providers 2
• Barium esophagography to evaluate for coexistent GER 2
• Chest radiograph to exclude pneumonia, foreign body, or structural abnormalities 8

Second-line investigations (if first-line negative or symptoms severe):

• Flexible bronchoscopy is indicated for suspected airway abnormality, though it assisted diagnosis in only 5.3% of private clinic cases versus 46% in tertiary centers 1
• Chest HRCT scan is the gold standard for airway structural integrity but should be used sparingly due to radiation risk (1 in 1,000 to 2,500 lifetime cancer mortality risk in young children) 1

Critical Pitfalls to Avoid

• Do not misdiagnose as asthma based solely on cough character—tracheomalacia and bronchomalacia are commonly mislabeled as asthma 1, 3
• Do not empirically treat with asthma medications unless other features (recurrent wheeze, reversible obstruction on spirometry) are present 7, 3
• Do not delay bronchoscopy if clinical suspicion for airway lesion is high, as recurrent infections and pneumonia can develop distal to the lesion 1
• Recognize that brassy cough has only moderate sensitivity (0.57), so absence of this quality does not exclude tracheomalacia 1

Management Considerations

• Conservative management with nebulized bronchodilators and medical therapy for GER is often effective for tracheomalacia 2
• Most cases of laryngomalacia/tracheomalacia resolve by age 2 years with conservative management 6
• Supraglottoplasty is reserved for severe disease or failure to improve 6
• Avoid cough suppressants and OTC medications in children under 6 years due to lack of efficacy and potential harm 7