Discussion

A total number of 4934 newly developed LA cases from 2010 to 2014 were analysed. This nationwide, population-based study was based on the KNHIS and KNICD that encompasses more than 90% of the total South Korean population and includes data such as the disease code, date of birth, history of hospital admission and prescriptions given. For a rare disease such as LA, a population-based study might be considered as an ideal setting to calculate the incidence and demographic characteristics. The average incidence of LA was 55.0 cases/100 000 person-years (table 1).

With the initiation of KDST in 2008, rather than visiting the paediatrician after the development of clinical symptoms, children could get a free yearly health check-up to ensure the proper growth and development. Reported cases of LA have abruptly increased from 101 cases in 2005 when the KNICD started gathering healthcare-related data to 1489 cases in 2014. This increase in LA cases with the initiation of the KDST registry can be explained by the role of vigilant inspection of the physician, enabling the inclusion of asymptomatic LA cases (figure 1). As the KDST registry was voluntary rather than mandatory and the referral to the paediatric gynaecologist was based on the primary physician’s discretion, the data in this study fall short of representing the real number of LAs in South Korea. With all the shortcomings standing, the strength of this study still lies in the involvement of 4934 newly developed LA cases, which is quite large a number considering the rarity of LA.

In this study, the group of 13 to 24 months showed the highest average incidence of 183.6 cases/100 000 person-years (95% CI 175.8 to 191.6) (table 2, figure 2). McCann et al reported a much higher incidence where 35 out of 90 girls being examined (38.9%) showed LA. The use of magnified colposcopy photographs as diagnostic tool might have included very small lesions that could have been easily missed with naked-eye observation.8

Some authors even argue that LA might be considered as an incidental normal finding in female infants because the small size of the external genitalia provides a natural opportunity for the labia to lie in apposition for most of the day resulting in temporal formation of LA.9 No long-term follow-up of untreated LA has ever been conducted, rendering the natural course of LA to be revealed.

In contrary to the possibility of spontaneous remission of LA, the importance of prudent physical examination and proper treatment of LA in referred patients of intractable recurrent urinary tract infection (UTI) has been emphasised by Melek et al. None of the primary physicians performed a gynaecological examination and only focused on urine culture, cystoscopy and ultrasonography. For the avoidance of unnecessary invasive procedures, the importance of physical examination to rule out LA was emphasised.10

The relative risk of acquiring LA in the age group of 13 to 24 months was 1.481 (95% CI 1.381 to 1.587) compared with the reference age group of 0 to 12 months (table 3). This is the age bracket where diaper usage might cause constant irritation resulting in LA. Explaining the natural progression of LA that often results in spontaneous resolution and emphasising that this is not a congenital disease should calm the overly concerned parents with respect to the appearance of their child’s external genitalia occurring in the absence of overt symptoms. Fondling, masturbation, trauma or sexual abuse are some other external irritation factors causing LA.11

Management algorithms for LA start with the recognition of associated symptoms such as rash, recurrent UTI, dribbling of the urine due to outlet obstruction, and dysuria.5 If asymptomatic, follow-up without intervention may suffice because the primary goal of treating LA should be no other than the resolution of the clinical symptoms associated with it. If symptomatic, either oestrogen vaginal cream application or surgical separation might be options.12 13 As most of the studies published so far only included a small study population in a single institute, a larger study with the cooperation of multiple institutes is warranted to set up the ideal treatment algorithm and methodology.

Based on the population-based national registry, a total of 4934 newly developed LA cases in South Korea were analysed. The average incidence of LA was 55.0 cases/100 000 person-years from 2010 to 2014. The age group of 13 to 24 months showed the highest average incidence of 183.6 cases/100 000 person-years (95% CI 175.8 to 191.6), coinciding with the hypo-oestrogenic milieu and persistent irritation due to diaper usage. Proper hygiene as a means of treatment should be emphasised before considering unnecessary intervention and the chance of spontaneous resolution with proper lifestyle adjustment should be kept in mind. Further studies are needed to reveal the natural disease course and the significance of diagnosing asymptomatic LA cases.