Introduction
Laryngomalacia is a congenital abnormality of the larynx that leads to the inwards collapse of supraglottic structures upon inspiration. Reference Hassan, Emam, Mahmoud, Awad, Rezek and Abou-Taleb1, Reference Hassan, Emam, Mahmoud, Awad, Rezek and Abou-Taleb2 This condition is typically observed in neonate and infant populations.Reference Dobbie and White3 Although the exact epidemiology of laryngomalacia is relatively unknown, studies have found that Black and Hispanic infants may be at increased risk compared to White infants and low birth weight may be a strong predictor for developing laryngomalacia.Reference Klinginsmith, Winters and Goldman4 Laryngomalacia leads to several clinical complications. Most notably, laryngomalacia is the most prevalent cause of infant stridor.Reference Bedwell and Zalzal1, Reference Klinginsmith, Winters and Goldman4 Other clinical findings include feeding problems, failure to thrive and respiratory distress.Reference Bedwell and Zalzal1 As such, it is important to identify laryngomalacia in paediatric populations, as prolonged respiratory compromise may lead to acute and chronic medical challenges.
The etiology of laryngomalacia is unclear. A proposed contributory factor of laryngomalacia is vitamin D deficiency.Reference Hassan, Emam, Mahmoud, Awad, Rezek and Abou-Taleb2 Previous studies have found that vitamin D levels were lower in infants with laryngomalacia compared to a control group.Reference Hassan, Emam, Mahmoud, Awad, Rezek and Abou-Taleb2, Reference Bozkurt and Çelik5 One cause of vitamin D deficiency is decreased exposure to sunlight. The skin contains the provitamin D3 7-dehydrocholesterol, a precursor of vitamin D.Reference Knuschke6 Provitamin D3 is photoconverted to provitamin D3 via ultraviolet B radiation that penetrates the skin superficially.Reference Knuschke6 Thus, serum vitamin D levels increase with exposure to sunlight. As the duration of sunlight varies across different seasons, the present study hopes to investigate seasonal and regional differences of laryngomalacia in paediatric in-patient populations. One can predict that admissions for laryngomalacia admissions tend to be more frequent during the Winter and in the colder United States regions, due to a decrease in sunlight duration. In this retrospective cross-sectional study, we investigate hospital admissions for laryngomalacia in different regions of the United States.
Methods
Database selection
The Healthcare Cost and Utilization Project (HCUP) Kids’ Inpatient Database (KID), during the year of 2016, was used for data analysis. This database is one of multiple databases offered by HCUP every three years, which are sponsored by the Agency for Healthcare Research and Quality.7 The KID was chosen as it includes information on a large sample of paediatric in-patient visits across the United States, allowing for the analysis of rare conditions such as laryngomalacia. Data recorded in the database include primary and secondary diagnoses, procedure codes, patient demographics (gender, race payer status), hospital characteristics (regional, rural or urban status), in-hospital births and mortality, length of stay and charges.7 SPSS V27 for Macintosh (IBM. Armonk, NY, 2020) was used for all data analysis.
Patient selection
The KID database encompassing the 2016 calendar year was the first of the series to use International Statistical Classification of Diseases and Related Health Problems 10th Revision (ICD-10) coding.8 Laryngomalacia was identified by its associated ICD-10 code: Q31.5.8 Based on this coding, we created binary variables for the presence or absence of a diagnosis of laryngomalacia. In total, there were 6,266,285 weighted admissions recorded in this database for 2016. The age range for admissions ranged from zero to 20; however for this study, only children less than three years old were selected as this constitutes 86.3 per cent admissions containing an associated diagnosis of laryngomalacia in KID. The variable for admission month was split to create a season’s variable, where months 1–3 were labelled as winter, months 4–6 were labelled as spring, months 7–9 were labelled summer and months 10–12 were fall. The variable for the hospital region was split into four regions: Northeast, Midwest/Central, South and West. The states represented within each region are recorded in Table 1.
Geographic Distribution of U.S. States by Region and Inclusion in KID 2016 Dataset
Data analysis
All data were weighted using the validated HCUP database weighting method to normalize data to the population in the United States as KID guidelines report only a portion of all paediatric hospital admissions. Categorical variables were analyzed using Pearson’s chi-squared test to assess for differences in laryngomalacia cases by season and hospital region. A p-value less than 0.05 was the statistical cutoff for significance for the analysis in this study.
Results
General results
The frequency of laryngomalacia admissions was found to be 258.0 per 100,000. The frequency of admissions containing an associated diagnosis of laryngomalacia was significantly increased in the winter by 10.0 per cent (p < 0.005) and significantly decreased in the summer by 10.9 per cent (p < 0.005). In addition, the frequency of laryngomalacia admissions was significantly increased in the Northeast region by 9.3 per cent (p < 0.05) and Midwest or Central region by 18.6 per cent (p < 0.005) as well as significantly decreased in the South region by 7.4 per cent (p < 0.005) and West region by 11.1 per cent (p < 0.005).
Seasonal distribution of laryngomalacia
The frequency of laryngomalacia admissions per 100,000 in the four seasons are shown in Table 2.
Frequency of laryngomalacia admissions
The frequency of admissions with an associated diagnosis of laryngomalacia per 100,000 ranged from 230.0 to 283.9. The frequency of admissions with an associated diagnosis of laryngomalacia per 100,000 was increased in the winter (p < 0.005) and decreased in the summer (p < 0.005).
Regional distribution of laryngomalacia
The frequency of admissions with an associated diagnosis of laryngomalacia per 100,000 in the different hospital regions are shown in Table 3.
Regional Rates and Counts of Laryngomalacia Admissions per 100,000 Hospitalizations
The frequency of admissions containing an associated diagnosis of laryngomalacia per 100,000 ranged from 229.3 to 306.0. The frequency of admissions containing an associated diagnosis of laryngomalacia per 100,000 was increased in the Midwest or Central regions (p < 0.005) and Northeast region (p < 0.05) and decreased in the southern (p < 0.005) and western regions (p < 0.005).
Discussion
Our results show a seasonal and regional distribution of laryngomalacia in children less than three years old. Overall, we found that the frequency of admissions for laryngomalacia was significantly higher (p < 0.005) in the winter months and in the Midwest or Central and Northeast regions of the United States, conversely the frequency of admissions was significantly lower (p < 0.005) in the summer and in the South and West regions of the country (Tables 2 and 3). This pattern is consistent with the climates experienced in these regions. The Midwest and Northeast regions are characterized by colder temperatures and reduced sunlight exposure. While the South and West regions typically have milder winters, more abundant sunshine and warmer temperatures. All the regions of the country typically see reduced sunlight in the winter months and increased sunlight in the summer months. These findings strongly suggest that environmental factors, including temperature, humidity and average sunlight, may play a significant role in the development or exacerbation of laryngomalacia in young children, emphasizing the influence of regional climates on the occurrence of this condition.
An earlier study from 2020 found that serum vitamin D levels in infants under one year of age correlated with a diagnosis of laryngomalacia.Reference Bozkurt and Çelik5 In this study, the authors hypothesized that vitamin D deficiency may contribute to the pathogenesis of laryngomalacia by causing abnormal bone mineralization and muscle weakness.Reference Bozkurt and Çelik5 Overall, they found vitamin D levels to be significantly lower (p = 0.003) in the laryngomalacia group compared to the control group.Reference Bozkurt and Çelik5 Given the well-established mechanism of sunlight impacting vitamin D synthesis,Reference Bârsan, Chelaru, Râjnoveanu, Popa, Socaciu and Bădulescu9 this supports our findings of seasonal variation in the frequency of paediatric patient admissions for laryngomalacia. Another potential factor could be the effect of increased vitamin D and calcium in pregnant mothers during gestation, which is a direct effect of both season and region as well.Reference Wagner, Taylor, Johnson and Hollis10 Furthermore, it is likely that other factors not studied, such as viral infections, allergens and air pollution, may contribute to the development of laryngomalacia as these factors also vary between different seasons and geographic regions. These additional factors should be studied in the future to better understand the increased incidence of admission secondary to laryngomalacia by regions, independent of the seasons.
Although the findings of this study are limited, t hey still have significant clinical implications. Specifically, they suggest that healthcare providers should be aware of the seasonal and regional variation in the incidence of laryngomalacia and take this into account when developing diagnostic and treatment strategies for affected children. For example, providers in areas with higher rates of laryngomalacia may be more vigilant in monitoring for this condition and providing early intervention to prevent complications from delayed intervention. Similarly, providers may need to consider screening for vitamin D deficiency in infants and children with suspected or confirmed laryngomalacia for better risk stratification. Furthermore, providers may consider offering vitamin D supplementation to infants at high risk of laryngomalacia.
It should be noted that this study has limitations. First, the study relied on data from a single database, the HCUP KID, for the year 2016. While the HCUP database is certainly valuable for research purposes and well-reported in literature, future studies should expand the patient selection by using alternative databases which are larger. Additionally, the HCUP database only includes information on paediatric in-patient admissions and discharges, which may exclude some incidences of laryngomalacia in the general population or out-patient settings. This study also focused on patients less than three years old given it was the majority demographic of the dataset. It is possible that the correlation between region and season may be different or less significant in children over the age of three. Furthermore, the HCUP database used was specific to the year 2016; therefore, future studies should aim to investigate these relationships across a broader timeframe. Lastly, a limitation of the database used is that it did not include information on the severity or duration of the cases of laryngomalacia analyzed. Future studies should aim to investigate any underlying trends between seasonality, region and specific vitamin D levels with severity of laryngomalacia.
• The study investigated the link between geographic region, seasonality and hospital admissions for paediatric laryngomalacia
• Results revealed a significant seasonal and regional pattern in laryngomalacia cases, with higher admissions during winter and in the Midwest/Northeast regions and lower admissions during summer and in the South/West regions
• These findings suggest that environmental factors such as temperature, humidity and sunlight likely play a role in laryngomalacia development
• The study also found a connection between low vitamin D levels and laryngomalacia, supporting the observed seasonal variation
• Overall, these results have important clinical implications, indicating the need for healthcare providers to consider seasonal and regional variation when diagnosing and treating laryngomalacia in children, potentially including vitamin D supplementation for those at risk
Conclusion
In conclusion, this study found a seasonal and regional distribution of laryngomalacia in children under three years old. Specifically, the frequency of admissions for laryngomalacia was significantly higher in the winter months and in the Midwest or Central and Northeast regions of the United States. The frequency of admissions was significantly lower in the summer and in the South and West regions of the country. These findings suggest that environmental factors, such as temperature, humidity and average sunlight, may play a role in the development or exacerbation of laryngomalacia in young children. The results of this study have important clinical implications and suggest that healthcare providers should be aware of the seasonal and regional variation in the incidence of laryngomalacia and take this into account when developing diagnostic and treatment strategies for affected children. Future studies should expand the patient selection and use alternative databases to confirm these findings.
