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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Croup is usually viral, classically parainfluenza, causing barking cough, hoarseness, and inspiratory stridor
- Diagnosis is clinical; neck X-ray may show steeple sign but is not routinely needed
- All severities benefit from a single dose of dexamethasone
- Moderate to severe croup with stridor at rest needs nebulized epinephrine plus observation for recurrence
- Toxic appearance, drooling, tripod posture, muffled voice, or inability to swallow suggests epiglottitis or deep neck infection, not routine croup
Overview
Croup is inflammation of the larynx, trachea, and bronchi causing subglottic narrowing. It is usually viral and affects children from 6 months to 3 years. Symptoms are typically worse at night and may follow URI symptoms. The main clinical distinction is between mild croup that can be treated with dexamethasone and discharged, and severe upper airway obstruction requiring nebulized epinephrine and close observation.
Epidemiology
Croup is common in toddlers and preschool children, especially in autumn and early winter. Parainfluenza virus is the classic cause, but RSV, influenza, adenovirus, and other respiratory viruses can cause similar illness. Most cases are mild and self-limited. Severe airway obstruction is uncommon but can be life-threatening.
Clinical Features
Symptoms
Barking seal-like cough
Hoarse voice and inspiratory stridor
URI prodrome with rhinorrhea and low-grade fever
Symptoms worse at night and with agitation
Drooling, dysphagia, toxic appearance, or muffled voice
Rapid onset high fever or severe distress suggesting bacterial tracheitis or epiglottitis
Signs
Inspiratory stridor, especially when agitated; stridor at rest indicates more severe disease
Suprasternal/intercostal retractions or increased work of breathing
Normal oxygen saturation in many cases; hypoxemia is late and concerning
Barking cough with otherwise non-toxic appearance
Tripod positioning, drooling, or inability to lie down are red flags for epiglottitis/deep neck infection
Investigations
First-line
Clinical assessmentAssess work of breathing, stridor at rest, mental status, hydration, and oxygenation
Pulse oximetryUseful for moderate/severe cases; normal saturation does not exclude significant upper airway obstruction
No routine labs or imagingTypical croup is a clinical diagnosis
Second-line
Neck X-raySteeple sign may appear but is not required; thumbprint sign suggests epiglottitis
Viral testingUsually unnecessary unless it changes isolation or antiviral decisions during outbreaks
Airway evaluationIf atypical, recurrent, severe, or foreign body/anatomic lesion is suspected
Specialist
Emergency/ENT/anesthesiaSevere respiratory distress, impending airway obstruction, suspected epiglottitis, bacterial tracheitis, or need for intubation
PICUPersistent severe stridor, hypoxemia, exhaustion, or repeated epinephrine requirement
1
Mild croup
- Single dose dexamethasone 0.6 mg/kg orally, IM, or IV; lower doses may be used in some protocols
- Avoid upsetting the child; keep with caregiver and minimize invasive procedures
- Supportive care: fluids, antipyretics, return precautions
2
Moderate to severe croup
- Dexamethasone plus nebulized epinephrine for stridor at rest, significant retractions, or distress
- Observe after epinephrine because effects can wane and symptoms may recur
- Oxygen if hypoxemic; avoid unnecessary throat examination in severe upper airway obstruction
3
Airway emergency
- Signs include exhaustion, altered mental status, cyanosis, poor air movement, or decreasing stridor with worsening obstruction
- Call experienced airway team early; prepare for controlled intubation
- Consider alternative diagnoses: epiglottitis, bacterial tracheitis, retropharyngeal abscess, foreign body, anaphylaxis
4
Disposition
- Discharge if no stridor at rest, minimal work of breathing, normal oxygenation, good hydration, and reliable follow-up
- Admit for persistent stridor at rest, repeated epinephrine, hypoxemia, dehydration, or social concerns
Complications
- Respiratory failure: Rare but can occur with severe airway obstruction or fatigue
- Rebound symptoms: Nebulized epinephrine improves symptoms transiently; recurrence requires observation and reassessment
- Misdiagnosed epiglottitis or bacterial tracheitis: Toxic appearance and drooling require airway-focused management
- Dehydration: Poor intake and increased work of breathing can reduce hydration
- Recurrent croup: May suggest airway anomaly, GERD, allergy, or foreign body in selected cases
USMLE Step 2 CK Exam Tips
- 1Barking cough + inspiratory stridor in a toddler = croup
- 2All croup gets dexamethasone, even mild disease
- 3Stridor at rest = nebulized epinephrine plus observation
- 4Steeple sign is croup; thumbprint sign is epiglottitis
- 5Drooling, tripod posture, toxic appearance, and muffled voice are not routine croup — think epiglottitis
- 6Do not agitate a child with severe upper airway obstruction
- 7Parainfluenza is the classic cause
practicetest your knowledge on croup (laryngotracheobronchitis)Apply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — pediatrics and beyond.
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