Stridor, an abnormal, high-pitched breathing sound, is a common presenting symptom in pediatric primary care. It indicates turbulent airflow through a narrowed airway, and while often benign, it can be a sign of serious and potentially life-threatening conditions in children. Accurate differential diagnosis is crucial for timely intervention and optimal patient outcomes. This article aims to provide a comprehensive guide to the differential diagnosis of stridor in children for pediatric primary care physicians.
Understanding Stridor: Inspiratory, Expiratory, and Biphasic
Characterizing stridor based on its timing within the respiratory cycle is a critical first step in narrowing the differential diagnosis.
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Inspiratory Stridor: This is typically caused by lesions above the vocal cords, in the larynx or extrathoracic airway. The negative pressure during inspiration causes the floppy supraglottic tissues to collapse inward, leading to airway obstruction and the characteristic inspiratory stridor. Common causes include laryngomalacia, vocal cord paralysis, subglottic stenosis, and foreign body aspiration in the larynx.
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Expiratory Stridor: This type of stridor is usually associated with lesions below the vocal cords, in the intrathoracic airway, primarily the trachea and bronchi. Positive pressure during expiration exacerbates airway narrowing in these regions. Conditions such as tracheomalacia, bronchomalacia, and intrathoracic tumors or masses can present with expiratory stridor.
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Biphasic Stridor: Stridor that is present during both inspiration and expiration often suggests a fixed or relatively fixed lesion at the level of the glottis or subglottis. Subglottic stenosis, vocal cord paralysis (bilateral), and some cases of croup can manifest as biphasic stridor.
Key Components of the Differential Diagnosis
When evaluating a child with stridor, a thorough history and physical examination are paramount. Key aspects to consider include:
Age of Onset
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Neonatal Stridor: Stridor present from birth or shortly after is often indicative of congenital conditions like laryngomalacia, vocal cord paralysis, subglottic stenosis, or vascular rings. Laryngomalacia is the most common cause of congenital stridor, often worsening in the first few weeks of life and typically resolving by 12-18 months.
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Infancy and Early Childhood Stridor: In this age group, infectious causes such as croup (laryngotracheobronchitis) become more prevalent. Foreign body aspiration should also be high on the differential, especially in toddlers. Acquired subglottic stenosis, often post-intubation, can also present in infants.
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Stridor in Older Children: While infections like viral croup are still possible, consider less common etiologies like papillomatosis, tumors, or exercise-induced laryngomalacia (EIL).
Characteristics of Stridor
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Severity: Mild, intermittent stridor may suggest laryngomalacia or a resolving viral illness. Severe, constant stridor with respiratory distress necessitates immediate evaluation and intervention to secure the airway.
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Pitch and Quality: A high-pitched, musical stridor is typical of laryngomalacia. A harsh, barking cough and stridor are classic signs of croup. A muffled cry and stridor might suggest epiglottitis (though less common now due to Haemophilus influenzae type b (Hib) vaccination).
Associated Symptoms
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Fever: Fever is common in infectious causes of stridor like croup, epiglottitis, and bacterial tracheitis.
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Cough: A barking cough is characteristic of croup. A brassy cough may be seen in tracheitis.
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Feeding Difficulties: Dysphagia or feeding intolerance, especially in infants, may point towards conditions like vascular rings or vocal cord paralysis.
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Cyanosis: Cyanosis indicates significant respiratory compromise and requires immediate attention.
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Change in Voice/Cry: Hoarseness or a weak cry can be seen in vocal cord paralysis or laryngeal lesions.
A Practical Differential Diagnosis Checklist for Pediatric Stridor
To streamline the diagnostic process in pediatric primary care, consider this differential diagnosis checklist:
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Laryngomalacia: Most common cause of congenital stridor. Inspiratory stridor, often worsening when supine or agitated, improving in prone position. Consider flexible laryngoscopy for confirmation if persistent or severe.
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Croup (Laryngotracheobronchitis): Most common infectious cause of stridor. Usually viral, often parainfluenza virus. Barking cough, inspiratory stridor, fever. Steeple sign on AP neck X-ray (though not always necessary for diagnosis).
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Epiglottitis: Medical emergency. Less common due to Hib vaccine. Sudden onset of high fever, sore throat, drooling, muffled voice, inspiratory stridor, tripod positioning. “Thumbprint sign” on lateral neck X-ray. Do not examine the throat in primary care setting if epiglottitis is suspected – may precipitate complete airway obstruction. Immediate transport to hospital is critical.
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Bacterial Tracheitis: Can mimic croup initially, but progresses to toxic appearance, high fever, thick purulent secretions, stridor. May require bronchoscopy for diagnosis and airway management.
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Foreign Body Aspiration: Sudden onset of cough, choking, and stridor. May be inspiratory, expiratory, or biphasic depending on location. Chest and neck X-rays (inspiratory and expiratory) can be helpful, but foreign bodies may be radiolucent. Bronchoscopy is often diagnostic and therapeutic.
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Subglottic Stenosis: Can be congenital or acquired (post-intubation). Biphasic stridor is common. May present with recurrent croup-like symptoms. Laryngoscopy or bronchoscopy for diagnosis.
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Vocal Cord Paralysis: Can be unilateral or bilateral, congenital or acquired (e.g., birth trauma, surgery). Hoarse cry, feeding difficulties, inspiratory or biphasic stridor. Laryngoscopy for diagnosis.
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Vascular Ring: Congenital anomaly compressing the trachea and/or esophagus. Biphasic stridor, feeding difficulties, dysphagia. May require imaging studies like CT angiography or MRI for diagnosis.
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Peritonsillar or Retropharyngeal Abscess: While less typical for stridor, large abscesses can cause airway compromise, particularly in younger children. Fever, sore throat, neck pain, muffled voice, trismus. CT scan or ultrasound for diagnosis.
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Laryngeal Tumors/Papillomatosis: Rare in children, but should be considered in persistent or progressive stridor without other clear etiology. Laryngeal papillomatosis (recurrent respiratory papillomatosis – RRP) caused by HPV is the most common benign laryngeal tumor in children, often presenting with hoarseness and stridor.
Initial Management in Primary Care
The immediate management of stridor in pediatric primary care depends on the severity of symptoms and suspected underlying cause.
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Mild Stridor without Respiratory Distress: For suspected viral croup or mild laryngomalacia, conservative management at home may be appropriate, including cool mist humidification, oral hydration, and close observation. Consider a single dose of oral dexamethasone for croup. Educate parents on warning signs for worsening respiratory distress and need for urgent care.
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Moderate to Severe Stridor or Respiratory Distress: Administer supplemental oxygen if SpO2 is below 92%. Nebulized racemic epinephrine can be effective for croup and other causes of upper airway obstruction, providing temporary relief. Corticosteroids (oral or intravenous) are indicated for croup and may be beneficial in other inflammatory conditions.
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Impending Respiratory Failure: Recognize signs of impending respiratory failure: altered mental status, cyanosis, severe retractions, decreased air entry, and fatigue. Immediate activation of emergency medical services (EMS) is crucial. Avoid agitating the child, especially if epiglottitis is suspected. Position the child comfortably and provide blow-by oxygen if tolerated while awaiting transport.
When to Refer to a Specialist
Prompt referral to a pediatric otolaryngologist or pulmonologist is warranted in the following situations:
- Persistent or worsening stridor despite initial management.
- Uncertain diagnosis after initial evaluation.
- Recurrent episodes of stridor.
- Stridor associated with feeding difficulties or failure to thrive.
- Suspected structural airway abnormalities (subglottic stenosis, vascular ring, etc.).
- Need for flexible laryngoscopy or bronchoscopy for diagnosis or management.
Conclusion
The differential diagnosis of stridor in children is broad, ranging from benign, self-limited conditions to life-threatening emergencies. A systematic approach, considering the timing of stridor, age of onset, associated symptoms, and careful physical examination, is essential in pediatric primary care. Understanding the key differentiating features of common causes of stridor and knowing when to escalate care or refer to a specialist are critical for ensuring optimal outcomes for children presenting with this concerning symptom. Early recognition and appropriate management can significantly reduce morbidity and mortality associated with pediatric stridor.
