Croup (Viral Laryngotracheobronchitis)

Why is this topic important?

Croup is one of the most common causes of acute upper airway obstruction in childhood and a classic MRCPCH examination topic.

Candidates are expected to:

Recognise the typical presentation
Distinguish croup from epiglottitis and bacterial tracheitis
Understand the significance of stridor
Know the role of dexamethasone and nebulised adrenaline
Identify children requiring hospital admission

Croup is frequently tested through clinical scenarios involving a child with a barking cough and inspiratory stridor.

Definition

Croup is an acute viral infection causing inflammation and oedema of the:

Larynx
Trachea
Bronchi

The resulting narrowing of the upper airway causes:

Barking cough
Hoarse voice
Inspiratory stridor

Key MRCPCH Facts

Most commonly caused by Parainfluenza virus.
Usually affects children aged 6 months to 3 years.
More common during autumn and winter.
Barking cough is the classic symptom.
Inspiratory stridor indicates upper airway obstruction.
Dexamethasone is recommended for all severities of croup.
Nebulised adrenaline is used for severe croup.
Most cases are mild and self-limiting.

Anatomy and Pathophysiology

Why Children Are Vulnerable

Young children have:

Narrow upper airways
Relatively large tongues
Smaller subglottic diameter

Therefore, even minor swelling can cause significant airway obstruction.

What Happens in Croup?

Viral infection causes:

Inflammation
Mucosal oedema
Increased secretions

Most swelling occurs in the:

Subglottic Region

This is the narrowest part of the paediatric upper airway.

As swelling increases:

Airflow becomes turbulent
Stridor develops
Work of breathing increases

Causes

Viral Causes

Most common:

Parainfluenza virus type 1

Other causes:

Parainfluenza type 2 and 3
RSV
Influenza
Adenovirus
Human metapneumovirus
Coronavirus

Risk Factors

Age

Highest incidence:

6 months to 3 years

Environmental Factors

Exposure to respiratory viruses
Attendance at nursery
Siblings attending school

Seasonal Factors

Autumn
Winter

Clinical Features

Typical Presentation

Usually begins with:

Coryza
Low-grade fever

Followed by:

Barking cough
Hoarse voice
Inspiratory stridor

Mild Croup

Barking cough
No stridor at rest
Minimal respiratory distress

Moderate Croup

Stridor at rest
Mild to moderate recession
Increased work of breathing

Severe Croup

Marked stridor
Significant recession
Agitation
Respiratory distress

Impending Respiratory Failure

Reduced stridor
Exhaustion
Drowsiness
Cyanosis
Poor respiratory effort

This is a medical emergency.

Severity Assessment

Mild

Barking cough
No stridor at rest

Moderate

Stridor at rest
Mild respiratory distress

Severe

Significant stridor
Marked recession
Distress and agitation

Life-Threatening

Exhaustion
Cyanosis
Reduced consciousness
Silent airway

Differential Diagnosis

Epiglottitis

Features suggesting epiglottitis:

Drooling
Toxic appearance
High fever
Child sitting forward
Difficulty swallowing

Bacterial Tracheitis

High fever
Toxic child
Poor response to adrenaline

Foreign Body Aspiration

Sudden onset
Choking history
Asymmetrical examination

Retropharyngeal Abscess

Neck stiffness
Fever
Dysphagia

Anaphylaxis

Rapid onset
Urticaria
Facial swelling

Investigations

Usually Not Required

Croup is primarily a clinical diagnosis.

Important MRCPCH Point

Do not perform unnecessary investigations in a child with significant upper airway obstruction.

Agitation may worsen airway compromise.

Imaging

Usually not required.

A classical "steeple sign" may be seen on neck X-ray but is rarely necessary.

Management

General Measures

Keep child calm
Avoid unnecessary procedures
Encourage parental presence

Agitation increases airway obstruction.

Corticosteroids

Dexamethasone

Recommended for all severities of croup.

Benefits:

Reduces airway oedema
Improves symptoms
Reduces admission rates
Reduces need for further treatment

Nebulised Adrenaline

Used in:

Moderate to severe croup
Significant stridor at rest

Benefits:

Rapid reduction in airway swelling

Important:

Effect is temporary
Observation is required after administration

Oxygen

Administer if hypoxic.

Intensive Care

May be required if:

Severe airway obstruction
Respiratory failure
Need for intubation

Complications

Short-Term

Severe airway obstruction
Respiratory failure
Hospital admission

Rare

Need for intubation
Cardiorespiratory arrest

Prognosis

Excellent in the vast majority of children.

Common Exam Traps

Trap 1

Barking cough + stridor = croup until proven otherwise.

Trap 2

Inspiratory stridor indicates upper airway obstruction.

Trap 3

Dexamethasone should be given even in mild croup.

Trap 4

Nebulised adrenaline is for moderate or severe disease.

Trap 5

Drooling suggests epiglottitis rather than croup.

Trap 6

A quieter stridor in a deteriorating child may indicate worsening airway obstruction rather than improvement.

One Minute Revision

Common age: 6 months–3 years.
Most common cause: Parainfluenza virus.
Barking cough + hoarse voice + inspiratory stridor.
Stridor = upper airway obstruction.
Dexamethasone for all severities.
Nebulised adrenaline for moderate/severe disease.
Drooling and toxic appearance suggest epiglottitis.

Suggested References

NICE Clinical Knowledge Summary: Croup
RCPCH Guidance
BNF for Children
Nelson Textbook of Pediatrics
Illustrated Textbook of Paediatrics
Kendig's Disorders of the Respiratory Tract in Children
Advanced Paediatric Life Support (APLS)

Disclaimer

These notes are intended for MRCPCH revision and educational purposes only. They do not replace local, national or institutional guidelines. Clinical decisions should always be based on current guidance, senior advice and individual patient circumstances.

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