Croup

Croup (acute laryngotracheobronchitis) is one of the most common infectious pediatric emergencies seen in winter. Commonly caused by the parainfluenza virus, croup is characterized by inflammation of the larynx and trachea. The clinical presentation varies depending on the severity of airway obstruction, but typically includes a barking cough, hoarse voice, and inspiratory stridor, all of which tend to occur at night. In moderate to severe cases, respiratory distress with subcostal and intercostal retractions occurs. Croup is primarily a clinical diagnosis, although a chest x-ray may be used to support diagnosis; laboratory tests and pulse oximetry help assess the severity of disease. In mild cases, treatment aims at alleviating symptoms and involves cold, moist air, calming the child, and corticosteroids. Moderate to severe cases require racemic epinephrine. Complications are rare: in cases of respiratory insufficiency, supplemental oxygen is necessary or even sedation and intubation. The prognosis of uncomplicated croup is good, with complete recovery occurring within seven days of onset.

• Peak incidence: 6 months to 3 years
• Most common in fall and winter

References:^[1][2]

Epidemiological data refers to the US, unless otherwise specified.

• Most common pathogen: parainfluenza viruses (75% of cases)
• Second most common pathogen: respiratory syncytial virus (RSV)
• Other pathogens: adenovirus, influenza virus

References:^[1]

• Important membrane-bound virulence factors of parainfluenza virus include:
  • Hemagglutinin: binds sialic acid → viral entry
  • Neuraminidase: release and spread of virions
• Viral infection → inflammation of the upper airway with edema formation and infiltration of inflammatory cells → narrowing of subglottic airway (inspiratory stridor) and increased work of breathing

Prodromal phase

• Duration: 1–2 days
• Presentation
  • Rhinitis with nasal discharge and congestion
  • Low-grade fever
  • Possible erythematous pharynx

Laryngotracheal inflammation phase

• Duration: 2–7 days
• Presentation
  • Symptoms of croup primarily occur during the late evening/night.
  • Mild: seal-like barking cough, hoarseness, and mild inspiratory stridor due to subglottic narrowing
  • Moderate: dyspnea at rest, pronounced thoracic retractions, pallor, tachycardia > 160/min
  • Severe
    • Upper airway obstruction can cause pulsus parodoxus.
    • Severe tachydyspnea at rest with increasing respiratory failure, cyanosis, hypoxemia, bradycardia, and altered mental status.
  • Infants may become agitated as a result of breathing difficulties → worsens agitation and obstruction → in severe cases, exhaustion leads to the infant being unable to breathe on his or her own.

References:^[1][3][4]

Croup is primarily a clinical diagnosis, but imaging may be considered in mild cases of suspected croup. Other tests (e.g., pulse oximetry, blood gas analysis) help to assess the severity of disease. Identification of the viral pathogen is rarely necessary.

• Based on clinical findings (see “Symptoms/clinical findings” above)
• Pulse oximetry
• X-ray of chest and neck: helps to verify subglottic narrowing, usually called steeple sign
• In suspected cases of respiratory insufficiency: blood gas analysis (BGA)
• If pneumonia or bacterial tracheitis is suspected: CBC
• PCR: To identify the viral pathogen in tissue (e.g., nasopharyngeal washing)

References:^[1][3][5]

Others

• Asthma/obstructive bronchitis: asthma is characterized by intrathoracic narrowing, which leads to expiratory stridor. Croup, on the other hand, is characterized by extrathoracic narrowing, which leads to inspiratory stridor!
• Pneumonia: : No inspiratory stridor; mainly a productive cough, high fever, rales (bubbling sounds)

Laryngomalacia

• Epidemiology
  • Most common cause of congenital stridor
  • Symptoms begin within the first 2 months of life and peak at 6–8 months
• Pathophysiology: congenital abnormality of laryngeal cartilage; → increased laxity and collapse of supraglottic structures during inspiration → airway obstruction
• Clinical features
  • Usually happy and thriving infants
  • Inspiratory stridor: worsens in supine position, during crying, upper respiratory tract infections, agitation, and feeding
  • Reflux may be present
  • Failure to thrive and sleep-disordered breathing in severe cases
• Diagnosis: flexible laryngoscopy: collapse of supraglottic structures during inspiration and omega-shaped epiglottis
• Treatment
  • Reassurance (resolves by age 2 years in 90% of cases)
  • Supraglottoplasty in severe cases (e.g., severe hypoxemia, apnea, pulmonary hypertension, failure to thrive)

References:^{[5][6][7][8][9][10][11]}

The differential diagnoses listed here are not exhaustive.

Intubation in severe croup is difficult due to subglottic narrowing → anesthesiologist required!

References:^[3][6][12]

• Respiratory failure may occur in cases of advanced subglottic narrowing (very rare)
• Risk of asphyxiation
• Secondary bacterial infection
• Pulmonary edema
• Pneumothorax
• Pneumomediastinum
• Cardiac arrest and death

References:^[3]

We list the most important complications. The selection is not exhaustive.

• The prognosis in uncomplicated cases is good, with full recovery.
• Parents should be aware that croup tends to recur.
  • Most often within a week after recovery
  • If croup recurs within the peak incidence age (six months to three years), airway abnormalities should be suspected.
  • If croup recurs outside the peak incidence age, atopic conditions, airway lesions or gastroesophageal reflux should be suspected.

References:^[3]

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8. Steeple Sign (Trachea). https://radiopaedia.org/articles/steeple-sign-trachea. . Accessed: March 18, 2017.
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12. Epiglottitis. https://radiopaedia.org/articles/epiglottitis. . Accessed: March 18, 2017.
13. Lovinsky-Desir S. Laryngomalacia. In: Windle ML, Laryngomalacia. New York, NY: WebMD. https://emedicine.medscape.com/article/1002527. Updated: April 21, 2017. Accessed: December 12, 2017.
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