This is an original study that aims to investigate the correlation between urinary electrolyte levels and detrusor overactivity (DO) in children with primary monosymptomatic nocturnal enuresis (PMNE).

In this case control study, a retrospective analysis was performed on 60 PMNE children aged 5-12 years who were admitted to the First Affiliated Hospital of Zhengzhou University from February 2015 to January 2020. According to ambulatory urodynamic monitoring (AUM), 36 patients were categorized into nocturnal DO group [(19 males and 17 females, mean age(9.4±2.1) years, mean body mass index (BMI)(18.90±2.66) kg/m 2], and 24 patients, non-nocturnal DO group [16 males and 8 females, mean age(9.0±1.9) years, mean BMI(18.85±2.50) kg/m 2]. Daytime and nighttime urine volume and average urine electrolyte levels were measured. t-test, Chi-square test or Mann-Whitney U test were used for comparison between groups. Spearman rating coefficient was used to evaluate the correlation between average electrolyte level and maximum detrusor pressure during nighttime bladder storage.

There were no statistically significant differences in age, gender ratio, and BMI between the two groups (all P>0.05).The nocturnal urine volume [0.291(0.194, 0.408) L] and the frequency of nocturnal polyuria (33.0%) in the nocturnal DO group were significantly lower than those [0.420 (0.298, 0.673) L and 62.5%](all P<0.05) in the non-nocturnal DO group.The levels of nocturnal urine sodium [(181.13±102.39) mmol/L], calcium [(3.68±2.44) mmol/L], and chloride [(147.89±57.21) mmol/L] in the nocturnal DO group were significantly higher than those [levels of nocturnal urine sodium [(132.15±67.42) mmol/L], calcium [(1.98±2.07) mmol/L], and chloride [(110.95±54.27) mmol/L] in the non-nocturnal DO group (all P<0.05).However, there was no statistically significant difference in the level of nocturnal urine potassium between the two groups ( P>0.05).The levels of diurnal urine sodium, potassium, calcium, and chloride showed no statistically significant differences between the two groups (all P>0.05) (Table 1). The levels of nocturnal urine sodium [(181.13±102.39) mmol/L] and calcium [(3.68±2.44) mmol/L] in the nocturnal DO group were significantly higher than the levels of diurnal urine sodium [(132.48±79.84) mmol/L] and calcium [(1.48±1.20) mmol/L](all P<0.05). However, there was no statistically significant difference in the levels of nocturnal urine potassium and chloride compared to diurnal levels (all P>0.05).In the non-nocturnal DO group, there were no statistically significant differences in the levels of diurnal and nocturnal urine sodium, potassium, calcium, and chloride (all P>0.05) (Table 2). Additionally, the level of nocturnal urine calcium in the nocturnal DO group was positively correlated with the maximum detrusor pressure during the bladder storage period ( r=0.501, P<0.05) (Figure 1).

This study revealed three key findings. First, the nocturnal DO group exhibited significantly lower nocturnal urine volume and reduced incidence of polyuria compared to the non-nocturnal DO group. Second, elevated nocturnal urinary electrolyte levels showed a positive association with detrusor overactivity. Third, higher urinary calcium levels correlated with increased maximum detrusor pressure during the storage phase. The mechanisms underlying these observations warrant further investigation.

The increased nocturnal urine sodium, calcium, and chloride levels in children with PMNE may be one of the important reasons for the occurrence of nocturnal bladder dysfunction.