Croup

Synonyms: Acute laryngotracheitis, acute laryngotracheobronchitis

• Viral upper respiratory tract infection causes nasopharyngeal inflammation that may spread to the larynx and trachea causing sub-glottal inflammation, oedema and compromise of the airway at its narrowest portion.
• The movement of the vocal cords is impaired leading to the characteristic cough. Occasionally fibrinous exudation with pseudomembrane formation may occur, causing further airway compromise.
• It is thought that some children that suffer recurrent bouts of spasmodic croup have a primarily allergic rather than infective aetiology for sub-glottal oedema.¹

• Parainfluenza virus types I, II, III and IV (thought to be responsible for about 80% of cases - type I causing 50–70% of severe cases)¹
• Respiratory syncytial virus
• Adenoviridae
• Rhinoviridae
• Enteroviridae
• Measles
• Metapneumovirus
• Influenza A & B (type A associated with severe disease)
• Mycoplasma pneumoniae (causes the condition very rarely)

• The annual incidence is variable depending on the cyclical prevalence of viral infection (particularly parainfluenza virus) in children.²
• Peak incidence occurs in children aged 1–2 years and is around 60 per 1,000 child years.³
• Long-term studies show an annual prevalence averaging at about 3% in those aged <6 years.⁴

Risk factors

• M:F preponderance is about 1.5–2:1¹
• Commonest in those aged 6 months to 3 years
• Rare in those older than 6 years of age, but can affect some children up to the early teenage years
• Most prevalent in autumn and spring

Symptoms

Croup normally starts with non-specific symptoms of viral URTI such as runny nose, sore throat, fever and cough:

• This progresses over the course of a couple of days to include the characteristic barking cough (some describe it as akin to the noise of a seal) and hoarseness. These symptoms tend to be worse at night.
• Stridor develops, sometimes suddenly, as the narrowing of the sub-glottal airways crosses a threshold at which airflow compromise begins.
• Parents may notice that their child is struggling to breathe and this, understandably, may prompt them to bring their child to their local out-of-hours GP service or emergency department.
• The illness tends to last for about 3–7 days but can persist for up to 2 weeks.

Signs

• There is a high degree of variability in clinical findings.
• It is unusual for the child to appear 'septic' or 'toxic'.
• Check vital signs (T,P,BP) and put on pulse oximeter – tachycardia is often present, hypotension is a sign of severe illness.
• There may be a mild-to-moderate fever.
• A barking cough and hoarse cry are nearly always present.
• Stridor (defined as a harsh, low-pitched noise heard during inspiration) may be heard at rest or only when the child is agitated or active.
• Respiratory distress with marked tachypnoea and intercostal recession may be noted.
• Be wary of the child with respiratory distress, but only quiet stridor, as this may indicate a severe case where the degree of airway-narrowing is so bad as to limit air movement and hence decrease the volume of the noise.
• Chest sounds are usually normal but can be decreased in volume where there is severe airflow limitation.
• Drowsiness, lethargy, cyanosis and intercostal recession that disappears despite increasing respiratory distress should be considered as red flags for impending respiratory failure.
• A low SaO₂ on pulse oximetry (<95%) indicates significant respiratory impairment.

• Epiglottitis
• Inhaled foreign body
• Inhaled noxious substance
• Acute anaphylaxis
• Bacterial tracheitis
• Diphtheria
• Laryngomalacia or other congenital cause of upper airway stenosis (e.g. aortic arch abnormality causing external airway compression)
• Peritonsillar abscess (quinsy)
• Retropharyngeal abscess
• Angioneurotic oedema
• Laryngeal mucosal lesions such as laryngeal web, papillomata and haemangioma
• Vocal cord paralysis

• The diagnosis is usually made on clinical grounds and blood tests add little.
• FBC may reveal a viral pattern differential white cell count, but is rather non-specific.
• Viral titres are used on occasion to decide whether patients should be treated in isolation, or to indicate a need for anti-viral therapy in the case of influenza A.
• Plain CXR can exclude other causes such as inhaled foreign body, epiglottitis, bacterial tracheitis or retro-pharyngeal abscess.
• Postero-anterior CXR, including the neck area, may reveal the 'steeple sign':
  • This is the presence of a steeple-shaped narrowing of the darker area caused by air in the upper trachea, revealing the sub-glottal narrowing of the airway.
  • Follow the link to the next reference for an image of this sign.¹
  • Lateral neck radiographs may also be employed to demonstrate a distended hypopharynx during inspiration.⁵
• These radiological tests are not very specific or sensitive, with a significant false-positive rate and up to 50% of croup sufferers do not have these findings.
• Direct or indirect laryngoscopy are not usually required but may be employed where the course of the illness is atypical or there is reason to suspect a congenital or other alternative cause for upper airway stenosis.

There are many clinical scoring systems for croup. The most commonly cited is the Westley clinical scoring system that classifies cases into mild, moderate or severe.⁶It appears to be useful as a research tool to assess the efficacy of interventions, but there is little proof of its clinical usefulness.¹ The classification of symptoms it uses can be subjective and open to inter- and intra-observer variation.
An overall assessment of the patient's condition, taking into account the red flags listed above, SaO₂ readings and the degree of respiratory distress may be an equivalent and simpler guide to deciding what therapy is required.

The modified Westley clinical scoring system for croup

• Inspiratory stridor:
  • Not present – 0 points
  • When agitated/active – 1 point
  • At rest – 2 points
• Intercostal recession:
  • Mild – 1 point
  • Moderate – 2 points
  • Severe – 3 points
• Air entry:
  • Normal – 0 points
  • Mildly decreased – 1 point
  • Severely decreased – 2 points
• Cyanosis:
  • None – 0 points
  • With agitation/activity – 4 points
  • At rest – 5 points
• Level of consciousness:
  • Normal – 0 points
  • Altered – 5 points

• Do not give antibiotics unless there are sound clinical reasons to suspect secondary bacterial infection.
• If the child is well enough, allow them to remain in the arms of their parent(s) during examination and management as this has a calming effect and is thought to reduce the effect of stress on respiratory impairment.

• Treated patients have fewer re-attendances or hospital admissions, and those that are admitted require shorter inpatient stays.
• Dexamethasone appears to be effective in mild cases as well as in those that have moderate or severe croup.⁸

On the whole complications are rare and case series show that <5% of children require hospitalisation and <2% of those admitted need intubation and ventilatory support.
Rarely, secondary bacterial infection can lead to pneumonia or tracheitis. Pulmonary oedema and pneumothorax are seen extremely rarely as sequelae.

• Mortality rates in intubated children are around 0.5%.¹
• Overall mortality is low at about 1 in 10,000.⁹