What is the most likely mechanism of wheezing in a 5-month-old infant with persistent wheezing since birth, who shows improvement with neck extension?

From the Guidelines

The most likely mechanism of wheezing in a 5-month-old infant with persistent wheezing since birth who improves with neck extension is laryngomalacia. This condition is characterized by the collapse of supraglottic structures during inspiration due to immature laryngeal cartilage. Laryngomalacia is the most common congenital anomaly of the larynx, typically presenting with inspiratory stridor rather than wheezing, but the symptoms can be confused. The improvement with neck extension is particularly telling, as this position helps open the airway by reducing the collapse of the floppy laryngeal structures. Most cases of laryngomalacia are mild and self-limiting, resolving by 12-18 months of age as the laryngeal cartilage matures and strengthens. No specific medication is typically required for mild cases, but positioning the infant with slight neck extension during feeding and sleep may help. For severe cases causing feeding difficulties, failure to thrive, or respiratory distress, surgical intervention such as supraglottoplasty might be necessary. Other conditions to consider in the differential diagnosis include tracheomalacia, vascular rings, or subglottic stenosis, but the improvement with neck extension strongly suggests laryngomalacia as the primary mechanism.

Key Points

• Laryngomalacia is a common cause of wheezing in infants, especially those with persistent symptoms since birth.
• The condition is characterized by the collapse of supraglottic structures during inspiration.
• Improvement with neck extension is a key diagnostic clue, as it helps reduce the collapse of the floppy laryngeal structures.
• Most cases are mild and self-limiting, but severe cases may require surgical intervention.
• Other conditions, such as tracheomalacia, vascular rings, or subglottic stenosis, should be considered in the differential diagnosis, but laryngomalacia is the most likely cause given the improvement with neck extension, as suggested by the American Thoracic Society clinical practice guidelines 1.

Management

• Positioning the infant with slight neck extension during feeding and sleep may help alleviate symptoms.
• No specific medication is typically required for mild cases.
• Surgical intervention, such as supraglottoplasty, may be necessary for severe cases causing feeding difficulties, failure to thrive, or respiratory distress.

From the Research

Mechanism of Wheezing in Infants

The mechanism of wheezing in a 5-month-old infant with persistent wheezing since birth, who shows improvement with neck extension, can be attributed to several factors.

• The improvement with neck extension suggests that the wheezing may be related to a condition that affects the airways, particularly in the trachea or bronchi.
• Studies have shown that tracheomalacia, a condition characterized by a deficiency in the cartilaginous support of the trachea, can cause wheezing in infants 2, 3, 4.
• Tracheomalacia can lead to upper or central airway obstruction, which can cause wheezing, especially when the infant is in a certain position 2.
• The fact that the infant's wheezing improves with neck extension suggests that the trachea may be compressed or narrowed when the neck is in a neutral position, leading to wheezing 2.
• Other conditions, such as bronchomalacia, can also cause wheezing in infants, but the improvement with neck extension is more suggestive of tracheomalacia 3, 4.
• It is also important to consider other factors that may contribute to wheezing in infants, such as airway inflammation and remodelling, as well as developmental differences in airway mechanics 5.

Diagnostic Approach

A diagnostic approach to determine the underlying cause of the infant's wheezing should include:

• A careful medical history to document risk factors for persistent wheezing, including maternal smoking, feeding practices, environmental history, and family history of asthma or cystic fibrosis 6.
• A physical examination to assess for signs of airway obstruction, such as stridor or wheezing 6.
• Diagnostic tests, such as a chest radiograph or infant pulmonary function testing (IPFT), to evaluate the anatomy and function of the airways 6.
• Flexible fiberoptic bronchoscopy to visualize the airways and diagnose conditions such as tracheomalacia or bronchomalacia 2, 3, 4.