Discussion:
Stridor is one of the common respiratory finding observed in pediatric age group which is caused mostly by some obstruction in the upper airway. Stridor is not exclusively present in respiratory distress but could also have some central nervous system etiology. In the first year of life, Laryngomalacia is the most common cause of stridor (1). It presents typically in the first few weeks after birth, may worsen in the first 4 - 8 months and usually resolves by 18 – 20 months of age (4). It is usually managed conservatively; but surgical management is necessary in cases with worsening respiratory distress (5). However, secondary airway lesions other than laryngomalacia may also be observed to cause stridor in pediatric age group. FB plays an important role in determining these causes of airway anomalies.
Various studies were performed worldwide to evaluate the cause of stridor in this age group by bronchoscopic evaluation (6,7,8). Most of the studies had laryngomalacia as the most common cause of stridor with an associated secondary lower airway anomaly. Laryngomalacia may be caused by multiple reasons. One of the most common cause of laryngomalacia is neurological, i.e. altered laryngeal tone due to abnormality of the laryngeal nerve (9). Reflux is said to be another important cause of irritation and edema of the supra-glottic airway which worsens airway obstruction (10). Laryngomalacia is mainly a clinical diagnosis having stridor which worsens with feeding and in supine position and decreases on prone positioning. Other associated features involve weight loss of failure to thrive. Infants with laryngomalacia are observed to have shortened aryepiglottic folds, floppy omega shaped epiglottis and redundant arytenoid tissue which prolapses over the glottis in every breathing cycle. In our study, there was a good correlation (95.23%) between clinical diagnosis and bronchoscopic findings in cases with suspicion of Laryngomalacia.
There may be other causes of stridor beyond laryngomalacia. In a study conducted by Martin et al, infra-glottic stenosis, laryngeal inflammation and vocal cord paralysis were the most common findings on bronchoscopy in children with stridor (11). In other study by Erdem et al, laryngomalacia was the most common cause for stridor followed by other causes like subglottic stenosis, tracheal compression, laryngeal cyst which comprised of 16.5% of the cases evaluated for stridor (1). In our study, laryngomalacia was the most common cause of stridor (29.41%) followed by subglottic stenosis (13.23%) and tracheomalacia (11.76%). Other findings included subglottic stenosis, tracheomalacia, foreign body aspiration, external airway compression etc. Subglottic stenosis involves narrowing of the airway encircled by the cricoid cartilage, below the glottis and above the first tracheal ring (12). It could be congenital or acquired. More than 90% of the acquired subglottic stenosis is secondary to endotracheal intubation (13). Foreign body aspiration is a very common cause of acute onset noisy breathing in pediatric age group. Classic history of acute onset choking or coughing might not be present in such cases. In the above study done by Erdem et al, 15% of the children with stridor required surgical intervention (1) as compared to 10.35% of the children requiring surgical intervention in our study.
Stridor improved with time in all cases as observed on follow up. Children with an underlying neurological ailment tend to have persistent stridor for a relatively longer duration (1). However, Yuen et al reported in his study that neurological abnormalities did not alter time to resolution of symptoms (14).
On the basis of various studies done in the past, it can be concluded that bronchoscopic evaluation is necessary in accurately diagnosing the exact cause of stridor as prompt treatment could be initiated. Pediatric bronchoscopy can be done by a trained pulmonologist, intensivist, surgeon or anesthetist and should be included among the primary investigations in evaluation of children with stridor.