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Overview – Acute Laryngotracheobronchitis (Croup)
Croup, medically termed acute laryngotracheobronchitis, is a common paediatric viral infection primarily affecting the upper airway. It leads to inflammation of the subglottic region of the larynx, often extending to the trachea and bronchi. The hallmark presentation includes a characteristic “barking” cough, inspiratory stridor, and respiratory distress. While often self-limiting, moderate to severe cases require prompt supportive management. This article reviews the pathophysiology, clinical signs, and treatment essentials relevant to medical students and junior doctors.
Definition
Croup (acute laryngotracheobronchitis) is a viral illness characterised by inflammation and oedema of the subglottic larynx, trachea, and bronchial tree, leading to upper airway obstruction. It primarily affects children under five years of age.
Aetiology
Viral Causes
- Parainfluenza virus types I, II, III (most common)
- Respiratory syncytial virus (RSV)
- Influenza A and B
Pathogenesis of Croup
- Initial upper respiratory tract infection (URTI).
- Viral invasion of the subglottic space triggers inflammation and mucosal oedema.
- Accumulation of thick, mucopurulent exudate narrows the airway, especially during inspiration.
- Results in classic stridor and barking cough.
Morphology
- Inflammation of the larynx, subglottic region, trachea, and upper bronchi
- Mucosal oedema and vascular congestion
- Subglottic narrowing visible on imaging (steeple sign on AP neck X-ray in some cases)
Clinical Features
Typical Presentation
- Age group: 6 months to 5 years
- Sudden onset following a prodromal viral illness
Classic Triad – “The 3 S’s”
- Stridor (inspiratory)
- Subglottic swelling
- Seal-like barking cough
Additional Features
- Hoarseness
- Low-grade fever
- Respiratory distress, with nasal flaring, intercostal recessions
- Cyanosis in severe cases
- Worse at night
Investigations
Usually a clinical diagnosis.
Imaging (only if atypical presentation or concern for alternative diagnosis)
- Neck X-ray (AP view): may show the “steeple sign” — tapering of the upper trachea due to subglottic narrowing
Management of Croup
Mild Cases (No Stridor at Rest)
- Supportive care
- Oral corticosteroids: Dexamethasone (single dose)
Moderate to Severe Cases
- Nebulised adrenaline (epinephrine) for acute airway oedema
- IM/IV corticosteroids if oral route not tolerated
- Humidified oxygen
- Close monitoring for progression
- Hospital admission if respiratory distress persists
Indications for Intubation
- Marked respiratory distress
- Persistent cyanosis
- Fatigue or reduced consciousness
Note: Antibiotics are not indicated due to viral aetiology.
Complications
- Respiratory failure due to airway obstruction
- Secondary bacterial tracheitis
- Dehydration from poor oral intake
- Rarely, pneumothorax or pneumomediastinum
Differential Diagnosis
- Epiglottitis
- Bacterial tracheitis
- Foreign body aspiration
- Retropharyngeal abscess
- Allergic reaction/anaphylaxis
Summary – Acute Laryngotracheobronchitis (Croup)
Croup is a self-limiting viral illness of young children that presents with inspiratory stridor, a barking cough, and subglottic oedema. Management is typically supportive, with corticosteroids and nebulised adrenaline for moderate to severe cases. Recognising the signs of respiratory compromise is essential for timely escalation of care. For broader context, visit our Respiratory Overview page.