Croup

Definition/diagnostic criteria
Croup, or laryngotracheobronchitis, is an acute respiratory illness in children, characterised by inflammation of the upper airway, leading to airway narrowing and obstruction. It typically affects the larynx, trachea, and bronchi. The hallmark features are a barking cough, inspiratory stridor, hoarseness, and varying degrees of respiratory distress. Diagnosis is primarily clinical, based on the characteristic presentation of the barking cough and stridor, often following an upper respiratory tract infection (URTI).

Epidemiology
Croup is a common paediatric condition, primarily affecting children aged 6 months to 3 years, with peak incidence occurring in the second year of life. It is more prevalent in boys than girls and tends to occur more frequently in the autumn and early winter months. Croup is usually caused by viral infections, with the most common pathogen being parainfluenza virus (types 1, 2, and 3). Other viral agents include respiratory syncytial virus (RSV), adenovirus, and rhinovirus. In the UK, croup accounts for around 5% of respiratory illness in children, with most cases being mild and self-limiting.

Diagnosis

Clinical features
The characteristic clinical features of croup include a sudden onset of a barking cough, inspiratory stridor, and hoarseness. Symptoms typically begin at night and follow the prodromal phase of a URTI, which may include rhinorrhoea, fever, and mild cough. Stridor indicates narrowing of the upper airway, and its severity can be used to gauge the level of airway obstruction. Mild croup presents with stridor only during activity, while severe cases exhibit stridor at rest, increased work of breathing, and signs of hypoxia (e.g., cyanosis, fatigue).

Investigations
Croup is diagnosed clinically, and investigations are generally not required. Routine chest X-rays or other imaging are not necessary unless an alternative diagnosis is suspected (e.g., foreign body inhalation, bacterial tracheitis, or epiglottitis). In rare cases of severe or atypical presentations, a lateral neck X-ray may show the characteristic ‘steeple sign’ (subglottic narrowing) but is not routinely performed. Pulse oximetry may be useful in moderate-to-severe cases to assess oxygen saturation and guide the need for supplemental oxygen.

Treatment
Most cases of croup are mild and can be managed at home with reassurance and supportive care, such as ensuring adequate hydration. The mainstay of treatment for croup is corticosteroids, which reduce airway inflammation and improve symptoms. UK guidelines recommend oral dexamethasone at a dose of 0.15 mg/kg as first-line treatment. In the absence of dexamethasone, oral prednisolone (1-2 mg/kg) is an alternative, though dexamethasone is preferred due to its longer half-life and greater efficacy.

Hospital admission is warranted for children with severe respiratory distress, stridor at rest, or those who do not respond to initial medical treatment. Oxygen should be administered if oxygen saturations are below 92%. In rare cases of life-threatening croup, endotracheal intubation may be required, but this is an emergency intervention performed in secondary care.

Prognosis
The prognosis of croup is generally excellent. Most children improve within 48 hours, with symptoms peaking in the first 1-2 days and resolving within a week. The use of corticosteroids has significantly reduced the need for hospitalisation and the risk of serious complications. Rarely, children may develop secondary bacterial infections, such as bacterial tracheitis, which can lead to severe airway obstruction and require aggressive treatment. Recurrent episodes of croup, especially in older children, may suggest underlying conditions like asthma or airway anomalies, warranting further investigation.