Description

• Croup is a subacute viral illness characterized by upper-airway symptoms such as barking cough, stridor, and fever. “Croup” is used to refer to viral laryngotracheitis or laryngotracheobronchitis (LTB), although it is sometimes used for LTB with pneumonitis, bacterial tracheitis, or spasmodic croup.
• Most common cause of upper-airway obstruction or stridor in children
• Spasmodic croup: Noninfectious form with sudden resolution:
  • No fever or radiographic changes
  • Initially treated as croup
  • Usually self-limiting and resolves with mist therapy at home
  • Often recurs on same night or in 2–3 nights
• System(s) affected: Pulmonary and respiratory
• Synonym(s): Croup; Infectious croup; Viral croup; LTB

Epidemiology

• Predominant age (1):
  • Common among children 7 months–3 years
  • Most common during the 2nd year of life
  • Rare among those >6 years
• Predominant sex: Male > Female (1.5:1) (1)
• Timing:
  • Possible during any time of year but is most common in autumn and winter (with parainfluenza 1 and respiratory syncytial virus [RSV])

• 6 cases of croup per year per 100 children <6 years old
• 1.5–6% of cases require hospitalization.
• 2–6% of those require intubation.
• Decreasing incidence in the US and Canada

Risk Factors

• History of croup
• Recurrent upper respiratory infections
• Atopic disease increases the risk of spasmodic croup.

Pathophysiology

• Subglottic region/larynx is entirely encircled by the cricoid cartilage.
• Inflammatory edema and subglottic mucus production decrease airway radius.
• Small children have small airways with more compliant walls.
• Negative-pressure inspiration pulls airway walls closer together.
• Small decrease in airway radius causes significant increase in resistance (Poiseuille law: Resistance proportional to 1/radius⁴).

Etiology

• Usually viruses that initially infect oropharyngeal mucosa and then migrate inferiorly
• Parainfluenza virus:
  • Most common pathogen: 75% of cases
  • Type 1 is most common, causing 18% of all cases of croup.
  • Types 2, 3, and 4 are also common.
  • Type 3 may cause a particularly severe illness.
• Other viruses: RSV, paramyxovirus, influenza virus type A or B, adenovirus, rhinovirus, enteroviruses (coxsackie and echo), reovirus, measles virus where vaccination not common, and meta-pneumovirus
• Haemophilus influenzae type B now rare with routine immunization (2)
• May have bacterial cause: Mycoplasma pneumoniae has been reported.

Commonly Associated Conditions

If recurrent (>2 episodes in a year) or during first 90 days of life, consider host factors:

• Underlying anatomic abnormality (e.g., subglottic stenosis):
  • In 1 study, found to be present in 59% children with recurrent croup (3)
• Paradoxical vocal cord dysfunction
• Gastroesophageal reflux disease
• Neonatal intubation