Sleep disordered breathing (SDB) encompasses a group of diseases including primary snoring, upper airway resistance syndrome (UARS), obstructive sleep apnea (OSA), and central sleep apnea (CSA). SDB is characterized by having intermittent periods of abnormal respiratory patterns such as apnea, hypopnea, or respiratory effort-related arousals (RERAs)[1]. Primary snoring is not associated with apnea or hypopnea, while UARS is characterized by increased RERAs without obvious apnea or hypopnea[2]. Separately, OSA is characterized by the repetitive reduction or cessation of airflow during sleep, because of a partial or complete obstruction of the upper airway, resulting in subcortical or cortical arousals[1-3]. Such arousals can result in sleep fragmentation and nonrestorative sleep[3]. On the other hand, CSA is less common and occurs when the brain fails to transmit signals to the respiratory muscles; it is not associated with physical obstruction of the upper airway[1].

The night symptoms of pediatric SDB are loud and frequent snoring, mouth breathing, witnessed apnea during sleep, restless sleep, night sweats, and nocturnal enuresis. The daytime symptoms of pediatric SDB include morning headache, excessive daytime sleepiness, poor concentration, and mood problems[1,4]. Despite the various known symptoms of SDB, about 80% of people with SDB remain undiagnosed, due to the unawareness of their own condition[5]. Furthermore, polysomnography, the gold standard for diagnosing SDB, has limited accessibility, because it requires a night of sleep in a sleep laboratory, which is expensive, and requires trained examiners. Accordingly, several types of questionnaires about symptoms and complications were developed to screen patients at high risk for SDB whom may require further evaluation. Sleep questionnaires are considered as a valuable tool to evaluate in epidemiological research[6].

A pediatric sleep questionnaire (PSQ) was developed by Chervin to help identify SDBs without the expense of polysomnography. The PSQ consists of 22 questions and assesses relative symptoms of SDB including snoring, sleep behaviors, mouth breathing, daytime sleepiness, inattention, and hyperactivity. The possible responses to each question are “yes,” “no,” and “don’t know,” and the PSQ score is calculated according to the proportion of “yes” responses to the 22 questions, excluding the “don’t know” responses. When 8 or more positive answers to the 22 question-items were considered abnormal, both sensitivity and specificity were high, 0.81 and 0.87, respectively. Therefore, the optimal cutoff value for screening SDB was 0.33 points[6].

The prevalence of habitual snoring in children is in the range of 5% to 12%, while that of pediatric OSA is in the range of 1% to 4%[7]. In Korea, the reported prevalence rates of primary snoring and OSA in adolescents in a study were 11.2% and 0.9%, respectively[8]. In adults, it is reported that men have a greater risk of SDB than women, but this distinction is unclear in children. Several predisposing factors for pediatric SDB have been reported including adenotonsillar hypertrophy, obesity, micrognathia, and hyperglossia[1-3,9,10]. However, there is no study conducted on the risk factors for SDB in a large number of samples on Korean children. Thus, the aim of this study was to investigate the risk factors of SDB in children by comparing intraoral factors, body mass index (BMI), and medical history findings to PSQ outcomes.

The research protocol was reviewed and approved by the Institutional Review Board of Jeonbuk National University Hospital (CUH 2018-07-046).

SDB is a disorder that interferes with normal ventilation and sleep patterns due to increased upper airway resistance during sleep. It generally evolves from primary snoring to OSA[11]. In this study, children who always snore accounted for 4.8% of subjects, and the prevalence of potential SDB was 4.3%. In a literature review, the prevalence of primary snoring was in the range of 5% to 12%, while that of OSA was in the range of 1% to 4%[7]. Snoring in Korean children in the elementary school age range (occurring more than 3 days per week) was reported to be 7.1%, and children who reported snoring almost every day were reported at 4.3%[12]. Considering that a good screening test is sensitive rather than specific, the PSQ will be useful for screening patients for OSA rather than primary snoring.

Sleep questionnaires provide clinicians with comprehensive information about individuals’ habits and symptoms during sleep and daytime[13]. A number of sleep questionnaires have been developed for children, and the PSQ, has been widely studied and has shown adequate diagnostic validity[7,14]. Its optimal cutoff value for screening SDB was 0.33 points with a sensitivity of 0.81 and a specificity of 0.87[6]. The PSQ was able to discriminate 89% of the children with OSA from those with primary snoring[15]. It showed good internal consistency and test-retest reliability[6,16,17]. Thus, it can be regarded as a reliable screening tool that can be easily applied at the clinic or epidemiologic research.

Adenotonsillar hypertrophy and obesity are well-known as major risk factors of SDB in children[2,10]. The proportional size of the adenoid and tonsils increases during childhood between 3 and 8 years of age, which can make the airway narrower. The prevalence of pediatric SDB also increases in the period[2]. Likewise, the results of this study confirmed that tonsillar hypertrophy and obesity are definite risk factors of pediatric SDB. The risk of SDB was 6.8 times and 4.2 times greater in children who have tonsillar hypertrophy and obesity, respectively. It is notable that 45% of obese children with OSA have adenotonsillar hypertrophy, but the adenotonsillar size is smaller in the obese children with OSA versus OSA children who are not obese. This suggests that obesity can narrow the airway space. Thus, obese children with OSA are more likely to have adenotonsillar hypertrophy, but they may have limited improvement in OSA symptoms through adenotonsillectomy[3,10,18]. Allergic rhinitis in children can increase nasal resistance by causing nasal mucosal edema, which may aggravate pediatric SDB[2,19,20]. The results of this study also indicate that children with allergic rhinitis have a risk of SDB that is 4.5 times greater than that of others. Previous studies reported the association between atopic dermatitis and SDB, and this study also showed the association[21,22]. The risk of SDB was 2.8 times greater in children who have atopic dermatitis. Although the exact mechanism has not yet been elucidated, atopic dermatitis, considered inflammatory skin disease, shares many risk factors with SDB such as obesity, genetics, allergic diseases, environmental exposure, and it is speculated that they may influence each other’s disease expression[21].

Craniofacial factors related to narrow airway space including retruded mandible, midfacial deficiency, and high-arched palate are also associated with SDB[1,2]. Class II molar key status and excessive anterior overjet were used as methods of evaluating retrognathia. In the univariate analysis of this study, there was a significant difference of the prevalence of SDB between children with excessive anterior overjet and those without. However, no significant relationship was found in logistic regression analysis. Class II molar key status showed no significant association with SDB. Since it is caused not only by mandibular retrusion, but also by overgrowth of the maxilla, the class II molar key status does not correspond exactly with skeletal class II relationship. Therefore, additional analysis through radiographic examination is required, and early intervention with orthopedic treatment is recommended for children with craniofacial factors related to narrow airway space.

This study has significance in that, it identified the prevalence of SDB among Korean children and the characteristics of these children by including a relatively large number of subjects. Even though questionnaire has its validity, it still cannot definitely diagnose SDB alone. Nonetheless, because polysomnography for diagnosing SDB is costly and time-consuming, it is not suitable for large-scale epidemiological studies. Another limitation of the questionnaire is that the parents who completed the questionnaire may not sleep with their children, so they might not consistently notice symptoms such as an apnea during sleep. Despite this circumstance, the parent-reporting questionnaire used in this study is more objective than a selfreporting questionnaire, since it is difficult for children to recognize their own symptoms during sleep. In addition, although this study included a relatively large number of subjects, it does not represent the entire Korean children. Further research including individuals from various regions will be necessary to confirm the prevalence of SDB among Korean children.

Dentists examine the oral and maxillofacial structures of patients every day are familiar with these structures. Thus, if dentists have enough knowledge of SDB, they can play an important role in identifying risk factors to screen patients for SDB. If children who visit dental clinics are screened systematically and referred to an appropriate medical provider such as a pediatrician or otolaryngologist, the intervention will lead them to grow up healthy by receiving early treatment.

The aim of this study was to investigate the risk factors associated with SDB by comparing history taking and clinical examination with PSQ findings. Children at high risk for SDB accounted for 4.3%, and they were predisposed to tonsillar hypertrophy, allergic rhinitis, obesity, and atopic dermatitis. Children with these factors could be candidates for early intervention to prevent the progression of SDB.