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Background: The prognosis of steroid resistant nephrotic syndrome (SRNS) in children is poorer than steroid-sensitive cases. The diagnosis is made following the response to the initial 4-week corticosteroid therapy, which might be accompanied by side effects. However, predictive indicators at initial diagnosis remain unknown. We aimed to investigate whether selectivity index (SI) and other indicators at initial diagnosis, for example, serum immunoglobulin M (IgM) and total serum protein albumin ratio (TA ratio, total serum protein level over albumin level), can predict SRNS. Methods: Eighty children were enrolled from seven hospitals in Japan between January 2008 and December 2019 (mean age 4.7; male 65.0 %). Of the enrolled 80 children, 13 (16.3 %, M:F = 5:8) had been diagnosed as steroid-resistant after the initial treatment with steroids. The association between serum IgM (tertile categories; low: 24-133; middle: 134-169; and high: 169.1-510 mg/dl), SI (<0.2 or ≥0.2), and TA ratio (tertile categories; low: 1.8-2.6; middle: 2.62-3.75; and high: 3.8-15.3) at initial diagnosis and steroid resistance was evaluated with logistic regression adjusting for age and sex. Results: Low levels of serum IgM were significantly associated with steroid resistance (adjusted odds ratio (aOR) = 6.94; 95% confidence interval (CI): 1.12-43.11). TA ratio and SI were not significantly associated with steroid resistance. Conclusions: Low levels of serum IgM at initial diagnosis might predict steroid resistance among Japanese children with idiopathic nephrotic syndrome.

Patients with multisystem inflammatory syndrome in children (MIS-C) can develop clinical features resembling Kawasaki disease (KD). A full picture of MIS-C in East Asia which has higher incidence of KD than other regions remains unclear. We report on a 15-year-old Japanese boy with refractory MIS-C who was successfully treated with infliximab. A Japanese boy who was diagnosed with coronavirus disease 2019 (COVID-19) before a month developed MIS-C with fulfilling six principal symptoms of KD. Laboratory data showed extreme hyperferritinemia (11,404 ng/mL), besides lymphopenia and thrombocytopenia. The patient was refractory to initial therapy with intravenous immunoglobulin (IVIG; 2 g/kg), aspirin, and prednisolone. He was therefore administered a second IVIG (2 g/kg) and infliximab (5 mg/kg) on days 7 and 8 from the onset of fever, respectively, which resulted in an improvement of clinical symptoms. Only four Japanese cases with MIS-C were reported and all of them were responsive to IVIG. The hyperferritinemia in this case was distinctive from previously reported MIS-C cases in Japan and other cohorts and may be associated with refractoriness to IVIG therapy. Marked elevation of circulating ferritin levels is known to be induced by tumor necrosis factor-α, which plays a key role in the pathogenesis of both KD and MIS-C. Thus, for MIS-C patients with hyperferritinemia, early intervention with adjunctive infliximab may induce a more rapid resolution of inflammation and improve outcome. Because MIS-C may be heterogeneous with respect to immunopathology, genetic background, clinical phenotypes and response to therapies, optimized treatment strategies according to immunopathogenesis are required.

Many renal disorders are associated with changes in the size of the kidneys. Ultrasonography has widely replaced the intravenous urogram to evaluate kidney size in children suspected of having urinary tract abnormalities. We examined the kidney length (KL) of 195 children, 105 boys and 90 girls, aged 1 month-15.7 years, without urinary tract abnormalities. Here, we discuss the correlation between KL and age, height, and the distance between the 4th and 5th spinous processes of the lumbar vertebrae (lumbar segment L4-L5). KL showed a linear correlation with these somatic parameters. We noted a mean KL increase of 4.8 mm in boys and 4.6 mm in girls per 10 cm increase in height. The differences between the slopes of the regression lines for the lengths of both the right and left kidneys were also similar. The increase in KL was greater during the first 2 years of life, which mirrors the accelerated body growth during infancy. KL was generally 4-6 times longer than lumbar segment L4-L5. Only 0.5% of the girls, but none of the boys, showed a size that was less than 3.5 times the lumbar segment. We propose the use of the ratio of KL to lumbar segment L4-L5 to evaluate the kidney size as these values are readily available and are simpler to use than any other somatic parameter.