Croup (acute laryngotracheobronchitis) is one of the most common infectious pediatric emergencies seen in winter. Commonly caused by the parainfluenza virus, croup is characterized by inflammation of the larynx and trachea. The clinical presentation varies depending on the severity of airway obstruction, but typically includes a barking cough, hoarse voice, and inspiratory stridor, all of which tend to occur at night. In moderate to severe cases, respiratory distress with subcostal and intercostal retractions occurs. Croup is primarily a clinical diagnosis, although a chest x-ray may be used to support diagnosis; laboratory tests and pulse oximetry help assess the severity of disease. In mild cases, treatment aims at alleviating symptoms and involves cold, moist air, calming the child, and corticosteroids. Moderate to severe cases require racemic epinephrine. Complications are rare: in cases of respiratory insufficiency, supplemental oxygen is necessary or even sedation and intubation. The prognosis of uncomplicated croup is good, with complete recovery occurring within seven days of onset.
- Peak incidence: 6 months to 3 years
- Most common in fall and winter
Epidemiological data refers to the US, unless otherwise specified.
- Important membrane-bound virulence factors of parainfluenza virus include:
- 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
- Duration: 1–2 days
Laryngotracheal inflammation phase
- Duration: 2–7 days
- Symptoms of croup primarily occur during the late evening/night.
- Mild: seal-like barking cough, hoarseness, and mild inspiratory stridor due to subglottic narrowing
- Moderate: stridor and dyspnea at rest, pronounced thoracic retractions, pallor, tachycardia > 160/min
- Infants may become agitated as a result of breathing difficulties → worsens agitation and obstruction → in severe cases, exhaustion leads to the infant being unable to breathe on his or her own.
Croup is primarily a clinical diagnosis, but imaging may be considered in mild cases of suspected croup. Other tests (e.g., pulse oximetry, blood gas analysis) help to assess the severity of disease. Identification of the viral pathogen is rarely necessary.
- Based on clinical findings (see “Symptoms/clinical findings” above)
- Pulse oximetry
- X-ray of chest and neck: helps to verify subglottic narrowing, usually called steeple sign
- In suspected cases of respiratory insufficiency: blood gas analysis (BGA)
- If pneumonia or bacterial tracheitis is suspected: CBC
- PCR: To identify the viral pathogen in tissue (e.g., nasopharyngeal washing)
|Moderate to severe croup|| |
|Characteristics||Croup (subglottic laryngitis; laryngotracheitis)|| |
|Epiglottitis (supraglottic laryngitis)||Foreign body (FB) aspiration|
|Cause|| || || || |
|Onset|| || || || |
|General condition|| || || |
|Cough|| || || || || |
|Voice|| || || || || |
|Difficulty swallowing/drooling|| || || || || |
|X-ray findings|| |
|Response to inhalators|| || || || || |
|Additional|| || || || |
- Asthma/obstructive bronchitis: asthma is characterized by intrathoracic narrowing, which leads to expiratory stridor. Croup, on the other hand, is characterized by extrathoracic narrowing, which leads to inspiratory stridor!
- Pneumonia: No inspiratory stridor; mainly a productive cough, high fever, rales (bubbling sounds)
- Most common cause of congenital stridor
- Symptoms begin within the first 2 months of life and peak at 6–8 months
- Pathophysiology: congenital abnormality of laryngeal cartilage → increased laxity and collapse of supraglottic structures during inspiration → airway obstruction
- Clinical features
- Diagnosis: flexible laryngoscopy: collapse of supraglottic structures during inspiration and omega-shaped epiglottis 
The differential diagnoses listed here are not exhaustive.
Bacterial tracheitis 
- Definition: bacterial infection of the trachea, commonly following a viral infection of the respiratory tract
- More common in children < 6 years of age 
- More common during the fall and winter
- Clinical features
- Laboratory studies: leukopenia or leukocytosis, ↑ CRP and ESR
- Bronchoscopy: allows for a definitive diagnosis and relief of airway obstruction
- Respiratory failure may occur in patients with advanced subglottic narrowing (very rare).
- Risk of asphyxiation
- Pulmonary edema
- Cardiac arrest and death
We list the most important complications. The selection is not exhaustive.
- The prognosis in uncomplicated cases is good, with full recovery.
- Parents should be aware that croup tends to recur.