Croup (Laryngotracheobronchitis)

Croup is the commonest cause of acute upper-airway obstruction with stridor in young children. It is a viral inflammation of the larynx, subglottis and trachea that produces the classic triad of a barking ("seal-like") cough, hoarseness and inspiratory stridor. For NEET PG, the bankable facts are the parainfluenza aetiology, the radiological steeple sign, the Westley score, and dexamethasone + nebulised adrenaline as the therapeutic backbone.

Definition & terminology

The word croup derives from an old Scots verb meaning "to cry hoarsely." It denotes an acute, usually viral, inflammatory narrowing of the subglottic larynx and trachea, hence the formal name laryngotracheobronchitis (LTB). The subglottis is the narrowest part of a child's airway and is encircled by the rigid, non-distensible cricoid cartilage — the only complete cartilaginous ring in the airway. Even 1 mm of mucosal oedema here dramatically raises airway resistance (Poiseuille: resistance ∝ 1/radius⁴), explaining why small children decompensate fast.

Several entities are grouped under the croup umbrella, and distinguishing them is a classic exam point:

Entity	Nature	Onset	Fever / prodrome	Recurrence
Viral croup (LTB)	Infective, parainfluenza	Gradual over 1–2 days	Coryza + low-grade fever present	Sporadic
Spasmodic (recurrent) croup	Allergic / hyperreactive, often viral-triggered	Sudden, at night, no prodrome	Afebrile, child looks well between attacks	Recurrent, family/atopy history
Laryngotracheobronchopneumonitis	LTB + lower-airway/parenchymal spread	Progressive, toxic	High fever, often bacterial superinfection	—
Bacterial tracheitis	S. aureus exotoxic membranous tracheitis	Croup that worsens, toxic	High fever, poor response to adrenaline	—

High-yield: Spasmodic croup occurs suddenly at night in an afebrile, well-looking child with no preceding coryza and tends to recur — distinguish it from viral croup, which has a clear viral prodrome and fever. This viral-vs-spasmodic distinction is a repeatedly tested NEET PG point.

Epidemiology

• Peak age 6 months to 3 years (commonest at ~2 years). Rare beyond 6 years because the airway has widened.
• Boys > girls (~1.5:1).
• Autumn–early winter seasonality, mirroring parainfluenza circulation.
• Most cases are mild; only ~1–5% need hospitalisation and <1% need intubation.

Aetiology

High-yield: Parainfluenza virus type 1 is the single most common cause of croup (overall and of epidemic croup). Type 3 tends to cause more severe sporadic disease.

Pathogen	Notes
Parainfluenza 1	Most common cause overall; biennial autumn epidemics
Parainfluenza 2, 3	Type 3 → more severe sporadic cases
Influenza A and B	Tend to cause severe croup
RSV, adenovirus, rhinovirus	Less common
Measles	Croup in unvaccinated children; "membranous croup" historically
Mycoplasma pneumoniae	Occasional, older children

Note the contrast with diphtheria ("membranous croup" by Corynebacterium diphtheriae) and epiglottitis (classically Haemophilus influenzae type b) — both important differentials below.

Pathophysiology

Viral infection of the nasopharynx spreads caudally to the larynx and trachea. The hallmark is subglottic inflammation, mucosal oedema and fibrinous exudate. Because the cricoid ring cannot expand outward, swelling encroaches inward on the lumen.

The mechanistic flow:

Viral inoculation of nasopharynx → caudal spread to subglottis/trachea → mucosal oedema + ↑ secretions within the rigid cricoid ring → ↓ effective airway radius → turbulent airflow → inspiratory (and later biphasic) stridor + barking cough → if progressive → ↑ work of breathing → fatigue → hypoxia/hypercapnia → respiratory failure.

Stridor is inspiratory when obstruction is purely extrathoracic (negative intraluminal pressure on inspiration collapses the airway). As subglottic/tracheal narrowing becomes fixed and severe, stridor becomes biphasic (inspiratory + expiratory) — a sign of more significant obstruction.

Clinical features

Typical course: 1–3 days of coryza and low-grade fever, then abrupt onset (often at night) of the croup triad.

• Barking / brassy ("seal-bark") cough — the signature.
• Inspiratory stridor, progressing to biphasic stridor with severity.
• Hoarseness (laryngeal/vocal-cord involvement).
• Low-grade fever; symptoms classically worse at night and with agitation/crying.
• Tachypnoea, suprasternal/intercostal recession in moderate–severe disease.
• Restlessness, cyanosis, decreased air entry and altered consciousness signal impending respiratory failure.

Crucially, the child with simple croup looks non-toxic, can swallow, has no drooling, and prefers no particular posture — the opposite of epiglottitis.

High-yield: A child who is drooling, dysphagic, toxic, sitting in the tripod/sniffing position and prefers NOT to cough has epiglottitis, not croup. Do not examine the throat or lie the child down — risk of total airway obstruction.

Westley croup score

The Westley croup score grades severity (max 17) and is the most cited croup scoring system.

Parameter	0	1	2	3	4	5
Level of consciousness	Normal	—	—	—	—	Disoriented
Cyanosis	None	—	—	—	With agitation	At rest
Stridor	None	With agitation	At rest	—	—	—
Air entry	Normal	Decreased	Markedly decreased	—	—	—
Retractions	None	Mild	Moderate	Severe	—	—

Interpretation:

Score	Severity	Approach
≤ 2	Mild	Oral/IM dexamethasone, discharge, supportive care
3–7	Moderate	Dexamethasone ± nebulised adrenaline, observe
8–11	Severe	Dexamethasone + nebulised adrenaline, O₂, admit, close monitoring
≥ 12	Impending respiratory failure	Above + prepare for intubation/PICU

High-yield: Westley score ≥ 8 = severe; ≥ 12 = impending respiratory failure. Memorise the five parameters: consciousness, cyanosis, stridor, air entry, retractions.

Diagnosis & investigation of choice

Croup is a clinical diagnosis. Investigations are not routinely needed and should never delay treatment of a distressed child.

• Radiograph — AP neck (frontal): the classic steeple sign / pencil-point / wine-bottle sign = symmetrical subglottic narrowing tapering upward. This is the high-yield imaging answer.
• Lateral neck X-ray: helps exclude epiglottitis — look for the thumbprint sign (swollen epiglottis). In croup the epiglottis is normal; ballooning of the hypopharynx may be seen.
• Pulse oximetry: monitors hypoxia; SpO₂ falls late.
• Flexible laryngoscopy: reserved for atypical, recurrent or non-resolving cases to exclude foreign body, subglottic stenosis, haemangioma.
• Viral PCR/cultures: epidemiological use only.

High-yield: Steeple sign on AP (frontal) neck X-ray = croup; thumbprint sign on lateral neck X-ray = epiglottitis. Investigation of choice for diagnosis remains clinical, but the named radiological sign is the steeple/pencil-point sign.

Management & drug of choice

Stepwise approach

1. Keep the child calm with the parent — crying worsens obstruction. Minimal handling.
2. Assess severity (Westley score, SpO₂, work of breathing).
3. Corticosteroid for ALL severities — single dose dexamethasone 0.6 mg/kg PO/IM/IV (effective even in mild croup; reduces oedema, return visits and admissions). Oral and IM are equally effective. Nebulised budesonide (2 mg) is an alternative if vomiting.
4. Moderate–severe / stridor at rest: add nebulised (racemic or L-) adrenaline 0.5 mL/kg of 1:1000 (max 5 mL). Onset within 10–30 min; effect wanes by ~2 hours — observe ≥ 3–4 hours for rebound before discharge.
5. Humidified oxygen / blow-by for hypoxia; Heliox may reduce turbulent flow in severe cases.
6. Severe / impending failure: PICU; intubation with a tube 0.5–1 mm smaller than predicted for age (subglottis is narrowed and oedematous).
7. Antibiotics are NOT indicated in viral croup; reserve for bacterial tracheitis or proven superinfection.

High-yield: Dexamethasone (0.6 mg/kg single dose) is given to every croup patient regardless of severity. Nebulised adrenaline is added when there is stridor at rest / moderate–severe disease; always observe for the rebound phenomenon before discharge.

High-yield: Mist/humidified-air tents have NO proven benefit in croup — an old practice now abandoned. Do not select "humidified mist therapy" as the evidence-based treatment.

Drug	Dose	Indication	Key point
Dexamethasone	0.6 mg/kg PO/IM/IV single dose	All severities	Long t½, single dose suffices
Budesonide (neb)	2 mg	If vomiting / cannot take oral	Equivalent to dexamethasone
Adrenaline (neb)	0.5 mL/kg of 1:1000 (max 5 mL)	Stridor at rest, moderate–severe	Watch for rebound — observe ≥3–4 h
Oxygen / Heliox	Titrate to SpO₂	Hypoxia / severe	Heliox lowers turbulence

Complications

• Respiratory failure requiring intubation (uncommon, <1%).
• Bacterial tracheitis (secondary S. aureus, also S. pyogenes, S. pneumoniae) — toxic child, poor response to adrenaline, thick purulent tracheal membranes; this is now the commonest cause of life-threatening airway obstruction in children (since Hib vaccination reduced epiglottitis).
• Post-obstructive pulmonary oedema after relief of severe obstruction.
• Pneumonia / pneumothorax / pneumomediastinum from severe coughing/positive pressure.
• Dehydration from poor intake.
• Rebound obstruction after adrenaline if discharged too early.

Key differentials

Feature	Croup (LTB)	Epiglottitis	Bacterial tracheitis	Foreign body	Retropharyngeal abscess
Organism	Parainfluenza	H. influenzae b	S. aureus	—	Polymicrobial
Age	6 mo–3 yr	2–6 yr	Any childhood	Toddler	< 6 yr
Onset	Gradual (1–2 d)	Sudden (hours)	Croup that worsens	Sudden, choking	Sub-acute
Fever / toxicity	Low / non-toxic	High / toxic	High / toxic	Absent	Present
Cough	Barking	Absent/minimal	Barking + purulent	Variable	Absent
Drooling / dysphagia	No	Yes	Variable	No	Yes, neck stiffness
Posture	Any	Tripod / sniffing	Any	Any	Hyperextended neck
X-ray sign	Steeple (AP)	Thumbprint (lateral)	Ragged tracheal membrane	Hyperinflation/atelectasis	Widened prevertebral space
Response to adrenaline	Good	None	Poor	None	None

High-yield: A "croup" that fails to respond to nebulised adrenaline and dexamethasone, with high fever and a toxic child, is bacterial tracheitis — needs IV antistaphylococcal antibiotics and often intubation.

Mnemonics & eponyms

• "Croup = Cough that's barking, Cricoid (subglottic), Children small, Calm them, Corticosteroids."
• Westley parameters — "Children Cry Severely After Running" → Consciousness, Cyanosis, Stridor, Air entry, Retractions.
• Steeple / pencil-point / wine-bottle / church-spire sign = AP neck X-ray of croup.
• Thumbprint sign = lateral neck X-ray of epiglottitis (eponymous descriptor worth knowing for the contrast MCQ).

Recently asked / exam angle

• Most common cause of croup → Parainfluenza virus type 1.
• Radiological sign of croup → Steeple / pencil-point sign on AP (frontal) neck radiograph (lateral shows the thumbprint of epiglottitis — a classic distractor swap).
• Single most important drug given to all croup patients → Dexamethasone 0.6 mg/kg.
• Indication for nebulised adrenaline → moderate–severe croup / stridor at rest; remember the rebound and mandatory observation.
• Viral vs spasmodic croup → spasmodic is sudden, nocturnal, afebrile, recurrent, atopic, well between episodes.
• Croup not responding to treatment + toxic child → bacterial tracheitis (S. aureus).
• Narrowest part of the paediatric airway → subglottis (cricoid ring).
• Westley score ≥ 8 = severe; ≥ 12 = impending respiratory failure.
• No proven benefit → humidified mist / cool-mist tents.
• Why a smaller ET tube → subglottic oedema narrows the lumen; choose a tube 0.5–1 mm smaller.

Rapid revision

• Croup = viral subglottic/laryngotracheal inflammation; peak age 6 months–3 years, boys > girls.
• Parainfluenza type 1 is the commonest cause; influenza causes the most severe disease.
• Triad: barking cough + inspiratory (→ biphasic) stridor + hoarseness, worse at night.
• The subglottis within the rigid cricoid ring is the narrowest, least distensible airway segment — explains rapid decompensation.
• Diagnosis is clinical; the named radiograph sign is the steeple sign on AP neck X-ray.
• Thumbprint sign (lateral) = epiglottitis, the great mimic — drooling, dysphagia, toxic, tripod posture, H. influenzae b.
• Westley score: 5 parameters; ≥ 8 severe, ≥ 12 impending failure.
• Dexamethasone 0.6 mg/kg single dose is given to all severities, even mild.
• Nebulised adrenaline for stridor at rest/moderate–severe — beware rebound; observe ≥ 3–4 h before discharge.
• Mist therapy and antibiotics are NOT routinely indicated; antibiotics only for bacterial tracheitis/superinfection.
• Spasmodic croup = sudden nocturnal, afebrile, recurrent, atopic child, well between attacks.
• Treatment failure + toxic child + high fever = bacterial tracheitis (S. aureus); the leading cause of severe paediatric airway obstruction post-Hib era.