Diagnosing Croup
Croup is diagnosed clinically based on the characteristic barking cough, inspiratory stridor, hoarse voice, and respiratory distress from upper airway obstruction, typically following upper respiratory symptoms. 1, 2
Clinical Presentation
The diagnosis of croup is primarily clinical and does not require laboratory testing in most cases:
- Classic triad: Barking (seal-like) cough, inspiratory stridor, and hoarse voice 1, 2, 3
- Prodrome: Low-grade fever and coryza (runny nose) typically precede the barking cough by 12-48 hours 1
- Age: Most commonly affects children 6 months to 3 years old 1
- Timing: Symptoms often worsen at night 2
- Respiratory distress: Variable degrees ranging from mild stridor only with agitation to severe distress with intercostal retractions and paradoxical abdominal breathing 2, 3
Severity Assessment
Assess severity by presence of stridor at rest and work of breathing 3:
- Mild croup: Stridor only when agitated or crying, no intercostal retractions at rest 3
- Moderate-to-severe croup: Stridor at rest with increased work of breathing (intercostal retractions, nasal flaring, tachypnea) 2, 3
- Life-threatening croup: Severe respiratory distress, paradoxical breathing, decreased air entry, altered mental status 2
Diagnostic Imaging
Radiographic imaging is not routinely necessary but may show the classic "steeple sign" (subglottic narrowing on anteroposterior neck/chest X-ray) when performed 4:
- Chest radiograph can reveal subglottic narrowing but should not delay treatment 4
- Imaging is primarily useful to exclude alternative diagnoses when the clinical picture is atypical 1
Etiology
Parainfluenza viruses (types 1-3) are the most common causative agents 5, 1:
- Parainfluenza types 1 and 2 most commonly cause croup syndrome 5
- Other viruses include respiratory syncytial virus, influenza, adenovirus, and human metapneumovirus 5, 4
- Viral testing is not routinely indicated for management but may be obtained for epidemiological purposes 5
Critical Differential Diagnoses to Exclude
Always consider and rule out life-threatening mimics before confirming croup 1:
- Bacterial tracheitis: Toxic appearance, high fever, purulent secretions 1
- Epiglottitis: Drooling, tripod positioning, toxic appearance, dysphagia (now rare due to Hib vaccination) 1
- Foreign body aspiration: Sudden onset without prodrome, unilateral findings, history of choking 1
- Retropharyngeal or peritonsillar abscess: Severe dysphagia, neck stiffness, asymmetric findings 1
- Angioedema: Rapid onset, urticaria, exposure history 1
- Pertussis: Cough lasting ≥2 weeks with paroxysms, post-tussive vomiting, inspiratory whooping sound (though whooping may be absent in vaccinated individuals) 6
Common Pitfalls
Do not agitate the child during examination, as this can precipitate complete airway obstruction in severe cases 2:
- Avoid unnecessary procedures (throat examination, IV placement) until airway is secured if severe distress present 2
- Croup in adults is rare; consider alternative diagnoses first 4
- Most croup is mild and self-limited, resolving within 48 hours 1
- Only 1-8% of croup cases require hospitalization, and less than 3% of hospitalized patients require intubation 1