Croup, also known as laryngo-tracheo-bronchitis, is a common respiratory condition predominantly affecting young children between 6 months and three years old. It affects approximately 3% of children annually and is most commonly seen between September and December.

It is characterised by upper airway inflammation, leading to symptoms such as a barking cough, hoarseness, and inspiratory stridor. It tends to be a mild, self-limiting illness but causes distressing symptoms, and severe cases that compromise the upper airway can occur. As medical professionals, understanding croup’s pathophysiology, clinical presentation, diagnosis, and management is crucial for effective care to affected patients.

Aetiology

Croup is usually caused by the parainfluenza virus (it is responsible for around 75% of cases). Other causative agents include rhinovirus, influenza and respiratory syncytial viruses. Bacterial croup is much less common, but it can also be caused by Mycoplasma pneumoniae and Corynebacterium diphtheriae.

Clinical features

The typical symptoms of croup are the characteristic barking cough, hoarseness, and stridor. The stridor is typically a harsh, low-pitched noise that is heard during inspiration. It can be heard at rest but is often only apparent when the child is agitated or active.

There is often a prodromal coryzal illness for 1-2 days before stridor begins. Symptoms usually peak at 1-3 days, with the cough often being worse at night. A milder cough may last for another 7-10 days.

Chest examination may reveal tachypnoea and intercostal recession. Breath sounds are usually normal but can be decreased in volume where there is severe airflow limitation. Drowsiness, lethargy, and cyanosis are ominous signs and should be considered red flags for impending respiratory failure.

Assessment of severity

There are several scoring systems used in the assessment of croup. One such system that is both commonly used in clinical practice and validated is the Westley croup score, which is scored as follows:

On the basis of this scoring system, children with croup can be divided into four levels of severity:

• Mild (score 0-2)
• Moderate (score 3-5)
• Severe (score 6-11)
• Impending respiratory failure (score 12-17)

Approximately 85% of children have mild croup, and only around 5% of children with croup will require hospital admission. Many children with mild croup (score 0-2) can be safely discharged from the Emergency Department.

Management

Dexamethasone and prednisolone are often used and reduce airway swelling. Oral dexamethasone has been shown to be superior to oral prednisolone. Steroids, however, do not shorten the duration of the illness. No definite standard dose for the use of dexamethasone has currently been agreed in the UK. The APLS guidelines, however, recommend a dose of 150 mcg/kg, with a suggested maximum single dose of 12 mg.

Nebulised budesonide can be used as an alternative if the child is vomiting. The dose of nebulised budesonide for children aged 1 month to 18 years is 2 mg. This dose may be repeated 12-hourly until clinical improvement is seen.

Nebulised adrenaline can be used in severe and life-threatening cases. The current APLS guidelines recommend a dose of 400 mcg/kg or 0.4 ml/kg of 1:1000 adrenaline (maximum 5 ml) with oxygen through a face mask. This produces a transient improvement beginning within 10-30 minutes and lasting for up to two hours. Adrenaline reduces the clinical severity of obstruction, and although the effects are short-lived, it will buy time for the corticosteroids to take effect and enable an experienced team to be assembled in case more invasive management is required.

Children with mild croup can usually be discharged home following a single dose of dexamethasone. Children with moderate croup, however, should be observed for a minimum of four hours following a dose of dexamethasone and then re-assessed. Children with severe croup should be admitted to hospital.

Prognosis

 The prognosis for croup is excellent, with mild cases tending to be self-limiting even without treatment. Symptoms usually resolve within 48 hours, and this is shortened if steroids are used. In the majority of moderate cases, the prognosis is also very good, and symptoms usually resolve without any significant complications.

Approximately 1-3% of children who require hospital admission require intubation. The overall mortality rate is estimated at 1 in 30,000 cases.

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