A 6-month-old girl from Mumbai is brought to the emergency department with a 3-day history of progressive respiratory distress, stridor, and a barking cough. Chest X-ray (frontal view) shows a narrowing of the subglottic trachea with a characteristic "pencil sign" or "steeple sign." The child is afebrile. What is the most likely diagnosis?

Explanation

## Diagnosis: Laryngotracheobronchitis (Croup) ### Clinical Presentation Croup is a viral infection of the larynx and trachea, most common in children aged 6 months to 3 years. **Classic Clinical Triad:** 1. **Barking cough** ("seal-like" or "croupy" cough) 2. **Inspiratory stridor** (worse at night) 3. **Hoarseness** (due to vocal cord inflammation) **Associated Features:** - Prodrome of upper respiratory tract infection (URI) symptoms - Low-grade fever or afebrile - Symptoms worse at night, often improving during the day - Self-limited course (3–7 days) ### Imaging Findings **Chest X-ray (Frontal/AP View):** - **Steeple sign** (or **pencil sign**): subglottic narrowing of the trachea due to subglottic oedema - The narrowed subglottic trachea resembles a church steeple or pencil point (rather than the normal shouldered appearance) - Narrowing is typically symmetric and extends below the glottis - Normal supraglottic structures **Lateral Neck X-ray:** - Subglottic narrowing best appreciated on frontal view - Lateral view may show subglottic narrowing and normal epiglottis ### Key Points **Key Point:** The steeple sign is the radiological hallmark of croup and results from subglottic oedema caused by viral inflammation (most commonly parainfluenza virus type 1). **Key Point:** Croup is typically afebrile or low-grade fever, whereas epiglottitis presents with high fever, toxic appearance, and drooling. This clinical distinction is crucial. **Mnemonic: CROUP** — **C**ough (barking), **R**espiratory distress (mild to moderate), **O**edema (subglottic), **U**pper airway (viral), **P**arainfluenza (most common virus) **Clinical Pearl:** The diagnosis of croup is primarily clinical. Chest X-ray is not routinely required unless the diagnosis is uncertain or to exclude other conditions (epiglottitis, foreign body, bacterial tracheitis). **High-Yield:** Viral causes of croup (in order of frequency): 1. Parainfluenza virus type 1 (most common, 75% of cases) 2. Parainfluenza virus types 2 and 3 3. Respiratory syncytial virus (RSV) 4. Influenza A and B 5. Adenovirus 6. Measles (in unvaccinated populations) ### Differential Imaging Features | Feature | Croup (Laryngotracheobronchitis) | Epiglottitis | Foreign Body Aspiration | Laryngeal Papillomatosis | |---------|----------------------------------|--------------|------------------------|-------------------------| | **Age** | 6 mo–3 yr | 2–6 yr | 1–4 yr | 2–5 yr | | **Fever** | Low-grade/afebrile | High fever, toxic | Variable | Afebrile | | **Cough** | Barking, seal-like | Absent/minimal | Acute onset | Chronic, progressive | | **Stridor** | Inspiratory | Inspiratory (severe) | Biphasic | Inspiratory/biphasic | | **CXR finding** | Steeple sign (subglottic) | Thumb sign (enlarged epiglottis) | Radiopaque FB or air trapping | Narrowed glottis, irregular margins | | **Epiglottis** | Normal | Enlarged, "thumb sign" | Normal | Normal | | **Onset** | Gradual (viral prodrome) | Acute, rapid deterioration | Acute (witnessed aspiration) | Insidious, chronic | ### Management ```mermaid flowchart TD A[Child with barking cough + stridor]:::outcome --> B{Clinical severity?}:::decision B -->|Mild| C[Supportive care + observation]:::action B -->|Moderate| D[Dexamethasone 0.6 mg/kg IM/IV]:::action B -->|Severe| E[Dexamethasone + nebulized epinephrine]:::action E --> F[Consider hospitalization]:::action C --> G[Reassess in 2-4 hours]:::decision D --> H[Most improve within 24-48 hours]:::outcome F --> H ``` **First-line Treatment:** - **Dexamethasone** 0.6 mg/kg (single dose, IM/IV/oral) - **Nebulized epinephrine** (1:1000, 0.5 mL/kg, max 5 mL) for moderate-to-severe cases - Supportive care: humidified air, fluids, antipyretics **Prognosis:** - Self-limited; most children improve within 3–7 days - Complications are rare (< 1%): subglottic stenosis (chronic croup), bacterial superinfection [cite:Grosfeld Pediatric Surgery 7e Ch 39; Caffey's Pediatric Diagnostic Imaging 13e Ch 54] ### Why Imaging? Chest X-ray is obtained to: - Confirm the diagnosis (steeple sign) - Exclude other diagnoses (epiglottitis, foreign body, bacterial tracheitis) - Provide reassurance to parents - Not routinely needed if clinical diagnosis is clear