OSAS In Young and Older Children: A Brief Review on the Role of Laryngomalacia

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longer periods. The present study is aimed to lyophilize influenza virus strain to study its
effects on infectivity and viral load.


Introduction
Laryngomalacia resolves spontaneously approximately in up to 80% of infants, but in the remaining cases some therapeutic approach is required [1]. Congenital laryngomalacia is a common cause of stridor in infants. Stridor is caused by a collapse of supraglottic structures during inspiration and in more serious cases this condition can cause failure to thrive, feeding difficult, aspiration and obstructive disordered during sleep. Stridor usually appears after first weeks of life and often increase during feeding, in supine position or in restlessness. The pathogenesis of laryngomalacia seems to be related to immaturity of laryngeal cartilages or abnormal sensorimotor integration that induce an inspiratory collapse of supraglottic structures [1,2]. Gastroesophageal reflux [GER] is frequently detected in association with LM. Several evidences suggested that the mucosal inflammation GER related worsens LM symptoms' while the negative intrathoracic pressure generated to overcome airway obstruction may predispose to GER in a vicious circle [2][3][4]. A study of Hadfield et coll. demonstrated that the surgical correction of laryngomalacia also improved GER as assessed by 24-h probe monitoring [5]. LM frequently is associated with congenital or acquired neuromuscular disorders with a prevalence that widely range from 8 and 50% [6]. Children with Down Syndrome have a high prevalence of airway obstruction at laryngeal and tracheal levels, particularly trachea-bronchomalacia.
Laryngomalacia is often described as being common in children with Down's syndrome, where is generally correlated to the hypotonia and gastro-esophageal reflux disease [7,8].
The incidence of OSAS in infants with laryngomalacia [LM] is unknown, although obstructive apnea can be a sign of severity of laryngomalacia [1,9]. A report conducted by Zalzal, et al. found that 80% of patients showed apneic events prior to treatment of supraglottoplasty. Other literature data on severe laryngomalacia described a similar picture, with an incidence of apnea ranging from 62 to 82% [10][11][12].The main diagnostic tool for the assessment of LM is the flexible fiberoptic laryngoscopy [FFL] that in small children is generally performed under general anesthesia.
To ensure the maintenance of a spontaneous breathing, inhalation anesthetics should be used [13,14]. The gold standard to diagnose OSAS for all ages is the standard polysomnography [PSG]. Since physiologic polysomnographic parameters widely vary with age, age-appropriate norms should be used according to recent AASM guidelines [15,16]. Sometimes laryngomalacia may contribute to OSAS also in older children [17]. Isaacson et al. in 1997 defined "state-dependent laryngomalacia [SDL]" as a condition that appear during sleep with stridor and obstructive respiratory disorders in a child who present normal breathing while awake [18].
It is unclear whether this type of laryngomalacia is a continuum of a congenital disease or rather a condition that independently develops due to both redundant mucosae prolapsing over the arytenoids upon inspiration and neuromuscular abnormalities [19]. Typically, children present with sleep-induced stridor, upper airway obstruction and apnea. Sleep-state dependent laryngomalacia is estimated to cause upper airway obstruction in 3.9% of children with OSA assessed prior to adenotonsillectomy [20]. A study of Goldberg et al. described 17 subjects with sleeponset LM; among these children 7 had underlying hypotonia and 10 showed LM associated with OSA. Why these patients have a normalappearing laryngeal examination when awake but LM when asleep is unclear [21].

Several classifications of congenital laryngomalacia have been
proposed, often based on anatomic abnormalities or dynamic changes observed during flexible laryngoscopy, although to date no codified classification system is accepted. Some static findings include omega-shaped epiglottis, acute angle of epiglottis (Holinger, et al.) and short aryepiglottic folds even though these anomalies do not consider the dynamic changes during spontaneous breathing [22]. The simplest used categorization, proposed by Olney and coll. includes the three following groups: type 1-anterior prolapse of the mucosa overlying the arytenoid cartilages; type 2-medial collapse of short aryepiglottic folds; type 3-posterior displacement of the epiglottis. Most subjects present with more than one type of obstruction [23]. Moreover, different combinations of the various types can be observed and often LM is associated with other airways lesions such as tracheomalacia, bronchomalacia, subglottic stenosis, and vocal cord paralysis [24].More recently Groningen This classification provides a more didactic categorization of laryngomalacia and may be useful to guide the surgical approach [25].

Diagnostic Tools
The DISE provides a global evaluation of sites of obstruction during sedation and therefore can identify the level and the severity of collapse [27,28]. This technique is frequently used to assess children with complex upper airway disorders. Among children with OSAS, the execution of sleep endoscopy may help to plane the best surgical approach, even though a standardized method of interpretation that ensure an acceptable agreement among operators is lacking. DISE can be also indicated for children who have persistent OSA after adenotonsillectomy or for older children with OSA but without tonsillar hypertrophy when a state dependent laryngomalacia is suspected [29]. A retrospective study of Boudewyns and coll. involving 28 two-year-old children, showed a finding of collapse of epiglottis in 6 patients and laryngomalacia in others 4 subjects. All the children had severe OSAS. Among these children, DISE was useful in surgical decision making in order to achieve a targeted treatment based on the site of obstruction [30].

Therapeutic Approach
Treatment of OSAS associated with laryngomalacia may include conservative management [such as wait and see approach, anti- Some evidences showed that also among cases of severe laryngomalacia and vocal cord paralysis with OSA, non-invasive ventilation through nasal CPAP can be an effective and safe alternative to surgery [35].The CPAP titration usually starts with low pressure [4 cm H2O] gradually increased until obstructive sleep events and oxyhemoglobin desaturations are overcome.
Monitoring of CPAP assessment is recommended every 6-12 months, since mask size and CPAP pressure should be modified according to child growth [36,37].However, this treatment is not always accessible, since a specialized medical/nursing staff and an adequate training program for parents are both essential for the CPAP success. To date, little evidences are available regarding the indications for polysomnography and others sleep studies in children with laryngomalacia. Recent guidelines suggest that polysomnography should guide therapeutic approach only in infants with laryngomalacia associated with cardiac/neurological diseases or complex malformation syndrome [1].
Nevertheless, we believe that in all cases of assessed laryngomalacia it is prudent searching for obstructive sleep disorders since the prevalence of SDB among these children could be more frequent than expected. Frequently LM is associated with some endoscopic findings suggestive of reflux arytenoid and posterior glottic edema, vocal fold edema and lingual tonsil hypertrophy [38]. A systematic review regarding the association between laryngomalacia and reflux and comprising a meta-analysis on 6 studies, showed a prevalence of 59% based on dual probe pH monitoring although this was not statistically significantly greater in laryngomalacia than in other respiratory diagnoses. Response to anti-reflux therapy showed weak evidence, and benefit was generally apparent only after several months of therapy. Moreover, the histological findings showed only mild laryngeal inflammation.

The authors concluded that any causal association between LM
and GER lacks an evidence base therefore randomized controlled trial of anti-reflux therapy against placebo would be needed [39].

The International Pediatric Otorhinolaryngology Group consensus
suggest an empirical approach recommending use of anti-reflux therapy if the child has feeding and/or respiratory problems, and 'only observation' if respiratory symptoms are mild and the growth is satisfactory [40].

Discussion
OSAS is an emerging disease that can cause significant morbidity at any age. Numerous studies suggest that SDB has a deleterious effect on infant's growth and intellectual development [9]. Infants with prolonged apnea often show lethargy, feeding difficulty, grown and developmental delay [41]. OSAS risk factors in infants differ from those of older children. Nevertheless, in early life as in older children, the presence of laryngomalacia can cause respiratory disorders requiring in the most severe cases some treatment.
The real incidence of concurrent OSA and laryngomalacia is probably underestimated. Among older children with Obstructive Sleep Apnea Syndrome and daytime behavioral disturbances, laryngomalacia incidence has been reported to be 3.9% [20].
Several studies have shown that from 20-75% of children may have some degree of persistent sleep disordered breathing after adenotonsillectomy. A picture of occult laryngomalacia has been identified as a reason for poor post-operative PSG improvement in patients with OSA that underwent adenotonsillectomy [42].
Described variants from the typical stridor that develops in infants include episodic, exercise induced, and late-onset laryngomalacia and tracheomalacia. The concomitant presence of neurological disorders and other co-morbidities could worsen symptoms. A precious recognition and treatment of the primary disorder is crucial. The gold standard for the detection of LM is the flexible fiberoptic laryngoscopy that can be performed in wakefulness in mild and less complex cases or under general anesthesia in those most at risk if a multilevel obstruction is suspected [14].
When a state dependent or late onset LM is suspected, DISE may be useful for the detection of the obstruction site and may be effective in diagnosing LM. Moreover, among older children with sleep respiratory symptoms and non-occlusive degree tonsils, DISE may be complementary to laryngoscopy in the diagnostic path.
Unfortunately, the severity of obstructive respiratory disorder is not always related to the severity of laryngomalacia or to a specific LM type. This finding is confirmed by a prospective cohort study of children with established OSA, where polysomnography not proved useful in determining the severity of laryngomalacia and in predicting the need for surgery. Among 25 infants with OSA, only 80 per cent underwent supraglottoplasty. Moreover, the apneahypopnea index did not correlate with a high laryngomalacia severity score and it did not differ between those undergoing surgery and those managed conservatively [43]. Nevertheless, other evidences showed that a targeted treatment of laryngomalacia frequently results in a significant improvement of OSAS and associated symptoms [19]. According to our opinion the search for sleep breathing disorders in children with stridor and suspected laryngomalacia is crucial, since several literature data found that children with LM and sleep apneas]have more symptoms and risk of complications such as impaired psychomotor development [20,21].
We believe that performing a Polysomnography [PSG] among children with stridor is recommended, since a pulse oximetric screening is often not sufficient in infants with suspected apneas associated with LM. Central apneas are in fact often present and may be normal at this age but they cannot be identified without a PSG. Recent guidelines on obstructive sleep disordered breathing in 1-to 23-month-old children, suggest that the therapeutic approach for young children with OSAS should be individualized according to age, etiology and severity and tools as of nasopharyngoscopy or DISE may be use to decide the type and appropriate sequence of interventions [9].

Conclusion
Concluding also according to our experience, an accurate endoscopic diagnosis is essential to ensure targeted treatment of both OSAS and laryngomalacia.