Epidemiology
- Peak incidence: 6 months to 3 years
- Most common in fall and winter
- Viral infections are more likely to be acquired and transmitted in cold temperatures and dry air
Etiology
- Most common pathogen: parainfluenza viruses (75% of cases)
- Other pathogens: respiratory syncytial virus (RSV), adenovirus, influenza virus
Pathophysiology
Viral infection → inflammation of the upper airway with edema formation and infiltration of inflammatory cells → narrowing of subglottic airway (inspiratory stridor) and increased work of breathing
Clinical features
- Prodromal phase: 1–2 days of upper respiratory tract infection symptoms (rhinitis, low-grade fever, sore throat)
- Symptoms of croup last 2–7 days and typically manifest in the late evening/night.
- Characteristic features include seal-like barking cough, hoarseness, and inspiratory stridor due to subglottic narrowing.
Diagnostics
Imaging
- X-ray chest and neck (anteroposterior and lateral)
- May identify subglottic narrowing on anteroposterior view (steeple sign)
- May identify subglottic narrowing on anteroposterior view (steeple sign)
Differential diagnostics
| Croup (subglottic laryngitis; laryngotracheitis) | Epiglottitis (supraglottic laryngitis) | Foreign body (FB) aspiration | |
|---|---|---|---|
| Cause | Viral: primarily human parainfluenza viruses | H. influenza type B | foreign body |
| Cough | Barking | Absent | Chocking |
| Voice | Hoarse | Muffled | Hoarseness or inability to speak indicate a laryngotracheal FB. |
| Difficulty swallowing/drooling | Absent | Present | Depends |
| X-ray neck and chest findings | Steeple sign (subglottic narrowing on chest x-ray) | Thumbprint sign (thickening of epiglottis on lateral neck x-ray) | Most FB are radiolucent |