Background Information on the epidemiology of idiopathic nephrotic syndrome (INS) in children, complications of INS and the side effects of steroid therapy is scarce. Methods The Japanese Pediatric Survey Holding Information of Nephrotic Syndrome, a nationwide cohort study, was conducted by the Japanese Study Group of Renal Disease in Children and enrolled 2099 children with newly diagnosed INS between 1 January 2010 and 31 December 2012. We conducted a follow-up study of the complications during the first onset and the patients’ prognosis in this cohort. Results We obtained follow-up data on 999 children (672 males) with a median age at onset of 4.5 years [interquartile range (IQR) 2.8–9.4] and a median follow-up period of 4.1 years (IQR 2.5–5.1). At the first onset, 24% of patients experienced severe acute kidney injury (AKI), defined as a serum creatinine increase to a level two or more times the baseline. On logistic regression analysis, age, hematuria, severe hypoalbuminemia (serum albumin <1.0 g/dL) and severe bacterial infection were not independent factors, but female sex {hazard ratio [HR] 1.5 [95% confidence interval (CI) 1.1–1.7]} and hypertension [HR 4.0 (95% CI 2.6–6.0)] were significantly related to AKI. During the observation period, ocular hypertension requiring treatment occurred in 17.4% of patients, among which 0.4% received surgical treatment. Progression to frequently relapsing nephrotic syndrome/steroid-dependent nephrotic syndrome in 3 years was seen in 44.2% of the patients and was shown by the Cox regression analysis to be significantly related to younger age and days until remission at the first episode, but not to sex, hematuria, the minimum serum albumin level or AKI. Two patients died during the observation period. One patient showed progression to end-stage kidney disease. Conclusion Based on the results of a multicenter questionnaire survey, the overall survival and renal survival rates were found to be excellent. However, proper management of complications, particularly in AKI and ocular hypertension, is mandatory.

Based on our nationwide survey, the incidence of INS in Japanese children is approximately 3-4 times higher than that in Caucasians. However, the male:female ratio and the age at onset were similar to those in previous studies. We are now planning a prospective cohort study to examine the course of INS in Japan.

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Although vaccination may precipitate relapses of nephrotic syndrome (NS) in children with idiopathic NS, no data are available regarding NS activity regarding influenza (flu) virus infections and NS relapses after receiving inactivated flu vaccines. We conducted a nationwide study of children aged 6 months to 15 years with idiopathic NS to assess the relationship between NS relapse, flu vaccination, and flu infections. We used a multivariate Poisson regression model (MPRM) to calculate the risk ratio (RR) for flu infection and for NS relapse in children with and without flu vaccination. Data of 306 children were assessed. The MPRM in all 306 children showed a significantly lower RR for flu infection (RR: 0.21, 95% confidence interval CI 0.11–0.38) and for NS relapse (RR: 0.22, 95% CI 0.14–0.35) in children receiving flu vaccination compared with unvaccinated children. In an additional MPRM only among 102 children receiving flu vaccination, they had a significantly lower risk for NS relapse during the post-vaccination period (RR: 0.31. 95% CI 017–0.56) compared with the pre-vaccination period. Although our study was observational, based on the favorable results of flu vaccinations regarding flu infections and NS relapse, the vaccine may be recommended for children with NS.

Combination treatment with intravenous immunoglobulin (IVIG) plus prednisolone is effective for prevention of cardiovascular complications in children with Kawasaki disease (KD). However, administration of prednisolone for approximately 20 d in this regimen causes adrenocortical suppression in a high proportion of treated children. To establish a simple method to screen for this suppression, we performed a prospective study on 72 children with KD treated with this regimen in our institution from February 2012 to March 2014. By performing ROC analysis of 21 initial patients treated between February and June 2012, a serum cortisol value at 09:00 h of 5 mcg/dL was established as a threshold for intact adrenocortical function, which is equivalent to a peak serum cortisol value of higher than 15 mcg/dL in the CRH stimulation test. Then, we applied this screening test to 51 subsequent patients treated between July 2012 and March 2014. Approximately 90% of the patients with morning serum cortisol values above 5 mcg/dL 2 to 6 mo after the cessation of initial prednisolone treatment had peak serum cortisol values exceeding 15 mcg/dL, suggesting the efficacy of this approach.